CSN Quantity Templates

  CSDMS Standard Names — Quantity Templates

• A CSDMS Standard Name must have an object part and a quantity part, with adjectives and modifiers (as prefixes) being used to help avoid ambiguity and identify a specific object and a specific, associated quantity. This document contains "quantity templates". For "object templates", see: CSDMS Object Templates.

• The "templates" listed below are not exhaustive, but they do address many commonly needed cases where the pattern may not be obvious. Additional templates will continue to be added over time.

• This page used to contain sections with titles like "Attributes of Channels". All of these sections have been moved to a separate page: CSDMS Standard Name Examples.

• Each template includes examples and explanatory notes, and many of them make reference to the CF Standard Names, sometimes using the abbreviation "CF".

• Quantity seems to be the best word choice here, see Quantity and Physical quantities. The word "attribute" is more general and may also be a good choice, but many attributes cannot be measured or quantified with a numerical value that has units. Here we define a quantity as an attribute of an object that has units. (But including dimensionless units like [m/m].)

• Quantity Suffix Pattern. A "quantity suffix" is a word like "anomaly", "component", "correction", "fraction", "increment", "limit", "magnitude", "offset", "scale", "step" or "threshold" (and in some cases "ratio") that produces a new quantity name from an existing quantity name (e.g. "elevation_increment", "time_step" and "length_scale"). The units are usually unchanged, but "fraction" and "ratio" are exceptions. While quantity suffixes are a common pattern in describing quantities, CSDMS is moving away from using them in standard names because they can also be expressed (with more flexibility) using an operation prefix. ( See the CSDMS Operation Templates.) For example, "east_velocity_component" can be expressed as "east_component_of_velocity". As an operation prefix, additional adjectives can be applied for clarity (when necessary) without losing parsability, as in "east_down_component_of_shear_stress". In addition, operations can be composed, as in "x_component_of_gradient_of_elevation", again without losing parsability.

• Operation_name + Quantity Pattern. An optional operation name can be added in front of a quantity name to create a new quantity name that often has different units. See: CSDMS Operation Templates.

• Process_name + Quantity Pattern. Many quantity names contain a process name modifier from the standardized list of CSDMS Process Names. Process names are nouns, not adjectives, so we would use "refraction_index" instead of "refractive_index". (Or "diffusion_coefficient" vs. "diffusive_coefficient", etc.) The templates for Process Attributes and Rates of Processes below provide many more examples.

• Object-in-Object Quantity Pattern. Some quantities require 2 objects/substances to be specified where one is contained within the other. Examples include: "concentration", "diffusion_coefficient", "partial_pressure", "relative_saturation" (see Humidity), "solubility" and "volume_fraction". CSDMS has experimented with using the reserved word "_in_" and the pattern: object = (object + "_in_" + object) for such cases as in:

carbon_dioxide_in_air + partial_pressure
carbon_dioxide_in_air + relative_saturation
carbon_dioxide_in_water + solubility
clay_in_soil + volume_fraction
helium_plume_in_air + richardson_number
sand_in_soil + volumraction
silt_in_soil + volume_fraction
visible_light_in_air + speed      ## (possibly; See the Constants in Physics template.)
water_vapor_in_air + dew_point_temperature
water_in_atmosphere + precipitation_leq-volume_flux

However, using this pattern causes related quantities to become alphabetically separated, like "clay_in_soil" + "volume_fraction" and "sand_in_soil" + "volume_fraction". For this reason, CSDMS is moving toward expressing the "in" relationship through object nesting (as used in the Part of Another Object Pattern). The examples listed above then become:

air_helium-plume__richardson_number
air_radiation~visible__speed
atmosphere_air_carbon-dioxide__partial_pressure
atmosphere_air_carbon-dioxide__relative_saturation
atmosphere_air_water~vapor__dew_point_temperature
atmosphere_water__precipitation_leq-volume_flux
soil_clay__volume_fraction
soil_sand__volume_fraction
soil_silt__volume_fraction
water_carbon-dioxide__solubility

As of 7/23/14, hyphens are used in certain contexts to bundle multiple words that are part of a single concept or object, such as "carbon-dioxide". This allows the object part of a name to be parsed (on underscores) into its component parts. For example, "atmosphere_carbon-dioxide" can be parsed into "atmosphere" and "carbon-dioxide". Without the hyphen, "carbon" and "dioxide" would be identified as two separate objects, with "dioxide' contained in (or a part of) "carbon".

Note that bubble_point_temperature, dew_point_temperature and frost_point_temperature also require one substance within another, as in: air_water~vapor__dew_point_temperature. See the Temperature template.

• Saturated Quantity Rule. When using the Object-in-object Quantity Pattern there are several quantities that refer to a system that is saturated or "at saturation". In these cases the word "saturated" is inserted in front of the quantity name to define a new quantity. Examples include:

air_water~vapor__saturated_partial_pressure
soil_water__saturated_hydraulic_conductivity
soil_water__saturated_volume_fraction    (i.e. water content)

While it is true that the soil is saturated in the first two examples, we use this rule instead of inserting "saturated" as an adjective in front of soil and instead of appending a suffix like "at_saturation", which doesn't fit our (object + quantity) pattern. This rule is natural in the sense that each of the "saturated quantities" listed above would be represented by a separate variable in a model, often denoted with a subscript such as "s".

• Object-on-Object Quantity Pattern. Some quantities require 2 objects/substances to be specified where one is "on" or in contact with the other. Examples often involve friction. In such cases we use the reserved word "_on_" and the pattern: object = (object + "_on_" + object), as in:

concrete_rubber__kinetic_friction_coefficient
pavement_rubber__static_friction_coefficient
 
Note: Maybe "-and-"or "-to-" would be better than "_on_" here.  We should also list
the two object names in alphabetical order to avoid two names for the same thing.

• Object-to-Object Quantity Pattern. When the quantity refers to a relationship between two objects, we use the reserved word "-to-" and the pattern: (object + "-to-" + object + quantity). The reserved word "-to-" can also be used for ratios. See the Ratio template. Examples include:

bear_brain-to-body__mass_ratio
earth-to-mars__travel_time
earth-to-sun__mean_distance
 

When two objects are required to define a quantity, the last 2 objects in the object part of the name are often used, as in:

carbon_hydrogen__bond_length
hydrogen_oxygen__bond_energy (See: Table of bond energies.)

In the last two examples, we put the two object names in alphabetical order to avoid two standard names for the same thing.

We may also be able to use this pattern in constructions like: "land_subsurface-to-surface_water + seepage_rate", or "land_subsurface_water-to-surface + seepage_rate" or "ground_water-to-surface_water + seepage_rate" or "land_subsurface-to-land_surface_water + seepage_rate".

• Object-or-Object Quantity Pattern. In some cases, a quantity may apply to either of two alternate objects, as in:

land-or-sea_surface_radiation~incoming~shortwave__energy_flux

• Quantity-to-Quantity Pattern. Although similar to the Object-to-object Quantity Pattern, this pattern is used when two quantities (measured on the same object) are needed to define a new quantity as in:

channel_x-section__width-to-depth_ratio
electron__charge-to-mass_ratio    charge to mass ratio
electron__mass-to-charge_ratio

Note that "hydraulic radius" is a valid quantity name, but could also be expressed as "channel_x-section" + "wetted-area-to-perimeter_ratio".

• Short Quantity Name Synonyms. There are several terms that may provide a "short name" or synonym for another quantity, such as:

aspect     = azimuth_angle_of_antigradient_of_elevation   (relative to a fixed axis)
density    = mass-to-volume_ratio   (but density sometimes has other meanings; use "mass_density" ??)
discharge  = water~outgoing + volume_flow_rate
slope      = magnitude_of_gradient_of_elevation
speed      = magnitude_of_velocity   (or even "motion_rate"; process_name + quantity)

• Incoming and Outgoing Quantity Rule. Fluxes, flows and vector quantities may either enter or exit a given object (viewed as a control volume). In these cases, it is therefore necessary to distinguish between "incoming" or "outgoing". As of 7/23/14, "incoming" and "outgoing" are used as standard adjectives in such cases, even though it is also possible to use the Process Name + Quantity Pattern and then choose a process name that indicates whether the quantity is "incoming" or "outgoing". As of 8/16/14, the adjectives "incoming" and "outgoing" (with hyphens) may be applied to the transported substance in the object part of the name. Examples include:

atmosphere_top_surface_radiation~incoming~longwave__energy_flux
atmosphere_top_surface_radiation~incoming~shortwave__energy_flux
lake_water~incoming__volume_flow_rate
lake_water~outgoing__volume_flow_rate
model_grid_cell_water~incoming__volume_flow_rate
model_grid_cell_water~outgoing__volume_flow_rate

Recall that "discharge" is a short synonym for "outgoing_volume_flow_rate". (The word "discharge" connotes an "outflow".) Note that "inflow" and "outflow" are valid process names. See the Discharge template.

Note: In the CF Standard Names, "incoming" is only used in one name (namely, "toa_incoming_shortwave_flux") while "outgoing" is used in only 6 names (always containing "toa_outgoing_longwave_flux" or "toa_outgoing_shortwave_flux"). Recall that "toa" = "top_of_atmosphere".

Absorptance

  base_quantity = "absorptance"
  Examples of Specific Quantities:
  "spectral_absorptance"

  Examples

atmosphere_air_radiation~incoming~longwave__absorptance

• Absorptance (also called "absorptivity" and "absorption factor") is the dimensionless ratio of the radiation intensity absorbed by something to the original, incident radiation intensity. It is a number between 0 and 1.

• Absorptance + Reflectance + Transmittance = 1. See Reflectance and Transmittance below.

• Various authors recommend using the terms: Absorptivity, Emissivity, Reflectivity and Transmissivity as properties of a pure material and Absorptance, Emittance, Reflectance and Transmittance as the analogous terms for the characteristics of a specimen or sample. See: Palmer, J.M. (1994) Chapter 25: The measurement of transmission, absorption, emission and reflection, Handbook of Optics, 2nd ed., Part II, M. Bass, editor, McGraw-Hill, NY. (A PDF file is available here.)

• At a given wavelength, absorptance = emittance.

• The quantity "spectral absorptance" is the absorptance associated with a specific wavelength.

• The term absorbance, although similar, is a different quantity that involves a log function.

• See: Absorbance, Attenuation coefficient, Beer-Lambert law, Mass attenuation coefficient, Opacity (optics), Reflectance and Transmittance.

Affinity

  base_quantity = "affinity"
  Examples of Specific Quantities:
  "chemical_affinity"
  "electron_affinity" (of an atom or molecule)

  Examples

chlorine_electron__affinity
magnesium-chloride_water__chemical_affinity
sulphuric-acid_water__chemical_affinity
water_electron__affinity 

• Chemical affinity is defined in terms of Gibbs free energy. It is a quantity associated with two chemical species (atoms, molecules, ions, etc.) and therefore uses the Object-to-object Quantity Pattern.

• See Chemical affinity, Electron affinity and Desiccant.

Age

  base_quantity = "age"
  Examples of Specific Quantities:
  "deposition_age"

  Examples

sea_bottom_sediment__deposition_age

• The quantity age indicates the elapsed time since something was first formed or created, whether it be sea ice, a person or a sediment deposit. It has units of time.

• Note that "deposition_age" follows the Process Name + Base Quantity Name Pattern.

• See Duration and Time.

Albedo

  base_quantity = "albedo"
  Examples of Specific Quantities:
  "black-sky_albedo"
  "blue-sky_albedo"
  "bond_albedo"
  "geometric_albedo"
  "visual_geometric_albedo"
  "white-sky_albedo"

  Examples

earth__bond_albedo
land_surface__albedo

• Albedo (also called "reflection coefficient") is the ratio of the power per unit area [W m-2] of electromagnetic radiation reflected by a surface to the original, incident power per unit area (or irradiance). It is a dimensionless number between 0 (for a perfectly black surface) and 1 (for a perfectly white surface). The word albedo comes from the Latin word for "whiteness".

• Reflectance is a very closely related concept but there does not appear to be a universally accepted distinction between albedo and reflectance. Some authors take them to be equivalent, others use albedo for an average over shortwave radiation and reflectance as a function of wavelength, others describe albedo as either "diffuse reflectance" or "broadband reflectance" etc.. Dingman (2002) in his book Physical Hydrology defines albedo as the average of reflectance over visible wavelengths. This ambiguity was already recognized in a 1917 paper by Louis Bell. There have been recent efforts by Schaepman-Strub (2006) and others to standardize the terminology in descriptions of satellite surface albedo products. See Reflectance below.

• There is an important distinction between Bond albedo and Geometric albedo, and a formula relating the two. Bond albedos are strictly between 0 and 1 while geometric albedos can be greater than 1. (Enceladus, a large moon of Saturn, reportedly has a bond albedo of 0.99 and a visual geometric albedo of 1.4.) Bond albedo takes all wavelengths and phase angles of electromagnetic radiation into account.

• To more accurately characterize the scattering properties of a surface, a Bidirectional Reflectance Distribution Function (BRDF) is often used. The integral of the BRDF over all viewing angles is called the Directional-hemispherical reflectance (DHR) or "black-sky albedo". There are two types of Bi-hemispherical reflectance (BHR). The first is often called "blue-sky albedo" (or "actual albedo"). The second -- often called "white-sky albedo" -- is the BHR under isotropic diffuse irradiance conditions (i.e. reflectance when there is only diffuse and no direct illumination, denoted as BHRiso). For many applications it is possible to approximate the albedo at a particular solar zenith angle as a linear combination of DHR (or black-sky albedo) and BHRiso (or white-sky albedo). The contribution from each is determined by D, the proportion of diffuse illumination. See: White-sky and black-sky albedo.

• A Lambertian surface is an idealized model. In this sense it is similar to "black body", "channel centerline", "earth ellipsoid" or "mean-sea-level datum".

• See: Albedo, Albedo discussion, Bidirectional Reflectance Distribution Function (BRDF), Bond albedo, Geometric albedo, Irradiance, Lambert's cosine law, Lambertian reflectance and Reflectance.

Altitude

  base_quantity = "altitude"

  Examples

airplane__altitude
balloon__altitude
projectile__altitude
skydiver__altitude
submarine_above-seafloor__altitude   (need "seafloor" vs. "bottom" for clarity here)

• There is a subtle but important difference between the quantities "altitude" and "elevation". The word altitude refers to the distance of an object (e.g. aircraft, air parcel or balloon) above the ground, regardless of the local elevation of the land surface. The word elevation refers to the distance of an object (typically a land surface) above a datum, such as the mean sea level datum. Elevation is one of the three Geographic coordinates used to specify a 3D location (i.e. elevation, latitude and longitude).

• A skydiver or aircraft pilot is interested in knowing their height above the ground, locally, especially with regard to landing. Barometric altimeters (or pressure altimeters) measure the distance above mean sea level (so elevation), but may then be corrected using a QFE setting so that they display an altitude of zero for a given airfield (regardless of its elevation above sea level). Radar and laser altimeters measure the height above the ground directly by measuring the time it takes for a signal to reflect from the land surface and return to the aircraft.

• The standard sport skydiving altitude is 12,500 feet AGL (Above Ground Level); sometimes up to 18,000 feet AGL.

• Can we also use "altitude" for the height of an object (e.g. particle, submarine) above the sea floor (i.e. height above seafloor)? Do we need an extra adjective, like "bathymetric_altitude" or "above-bottom_altitude" ? We could also use something like "particle-to-bottom" + "distance" or just "particle_bottom_distance". The current approach is to use "above-bottom" as a "place" or "part", in the object part of the name.

• The standard term "equilibrium line altitude" (ELA) is discussed in the Attributes of Glaciers template.

• Note that in the CF Standard Names, "altitude" is used as a synonym for "elevation".

• See: Altitude above ground level, Elevation, Height above average terrain (HAAT), Lowest safe altitude and Mean sea level.

• See the Elevation template.

Amplitude

  base_quantity = "amplitude"

  Examples

sea_surface_water_wave__amplitude    # wave~gravity
wave~airy__amplitude
wave~cnoidal__amplitude
wave~electromagnetic__amplitude
wave~seismic__amplitude
wave~stokes__amplitude

• "Amplitude" is a basic property of a periodic function or waveform, along with wavelength and wavenumber.

Angle

  base_quantity = "angle"

  Examples

azimuth_angle, bank_angle, bond_angle, camber_angle, caster_angle, declination_angle, depression_angle, dihedral_angle,
elevation_angle, exterior_angle, flare_angle, friction_angle, incidence_angle, inclination_angle, look_angle, nadir_angle, 
phase_angle, pitch_angle, polarization_angle, rake_angle, repose_angle, roll_angle, rotation_angle, scattering_angle,
shock_angle, slope_angle, solid_angle, spreading_angle, tilt_angle, torsion_angle, vertex_angle,
yaw_angle, zenith_angle

• The local azimuth angle, zenith angle, and elevation angle (the complement of the zenith angle, less often called "altitude angle") that can be associated with a 2D or 3D vector field are treated as operations in the CSDMS Standard Names. See the CSDMS Operation Templates for more information.

• There are two major conventions used for measuring angles. For bearings, the angle is usually measured clockwise from north, and this typically includes wind data. (We also need to clarify whether the wind is blowing "to" or "from" that direction.) Most other angles are measured the way you learned in high school, counterclockwise from the x-axis (or from the east). It is therefore important to specify the convention that is used. This can be done by including the appropriate <assume> tag in a model's Model Metadata File, chosen from the standardized assumption names on the CSDMS Assumption Names page. A smart framework would be able to convert between these two conventions, when necessary, after examining these <assume> tags. Note: We could also introduce "bearing" as another base quantity so that the metadata wouldn't be necessary.

• A bearing (to an observed object) can also be specified relative to the direction of travel of a vehicle (e.g. truck, ship or airplane) instead of relative to north. See: Bearing (navigation).

• A heading is the direction (usually given as a bearing) in which an object, such as a ship or airplane, is traveling. It is related to the course and track angle; see: Course (navigation).

• Note that "earth_axis" + "tilt_angle" uses the object name "earth_axis" to refer to a "part" of the Earth (Part of Another Object Pattern) and the quantity name "tilt_angle" follows the Process_name + Quantity Pattern. We use "tilt" vs. "tilting" as allowed by one of the Basic Rules. We use "earth_axis__tilt_angle" vs. "earth" + "axial_tilt_angle" in accordance with the Object vs. Adjective Rule.

• In the context of a satellite or airplane viewing the Earth's surface, the terms look angle and nadir angle are used to indicate the angle between straight down from the satellite (i.e. the nadir direction) and the ray that points from the satellite to a location on the Earth's surface. The complement of the "look angle" is often called the depression angle. The term "off-nadir angle" would be more descriptive but is not as widely used. "Zenith angle" and "elevation angle" are also complementary angles, typically used for a viewer on Earth's surface looking up at an object in the sky (e.g. the sun or a planet). Note: The terms "view angle" or "viewing angle" should not be used in this context because they have other, more common meanings related to a camera's "angle of view" or the angles from which a TV or monitor are being viewed.

• In the CSDMS Standard Names, the quantities "azimuth_angle_of_position_vector", "elevation_angle_of_position_vector" and "zenith_angle_of_position_vector" are used for an object viewed from the Earth's surface (e.g. satellite), while "azimuth_angle_of_look_vector", "depression_angle_of_look_vector", "nadir_angle_of_look_vector" are used for objects on the Earth's surface viewed from above (e.g. a satellite).

• The quantity angle_of_repose is called "repose_angle" in the CSDMS Standard Names. This may sound a bit strange when spoken, but this is outweighed by the benefits of following a standardized pattern.

• Many of these follow the Process_name + Quantity Pattern.

• CSDMS standard names use "aspect_angle" vs. "aspect" for clarity since we distinguish between "slope" and "slope_angle".

• bank_angle is related to banking (e.g. aircraft) in turns but may also be used in the context of channel banks. The object part of the name allows the same quantity name to be used in different contexts.

• In the context of wheeled vehicles, several angles are used such as: Camber angle and Caster angle (or Rake angle).

• Three Euler angles can be used to describe the orientation of a rigid body, but different conventions are used. These would have some adjective(s) inserted before "euler_angle".

• The term flare angle refers to an angle measured from the vertical or main axis. The verb "flare" means to gradually become wider. (e.g. bell-bottom pants) The term "spreading_angle" is very similar.

• See: Azimuth angle, Aspect (geography), Orbital inclination, Slope, Solid angle and Zenith angle.

Anomaly

  operation_prefix = "anomaly_of"

  Examples

atmosphere_air__anomaly_of_pressure   (i.e. difference from climatology)
atmosphere_air__anomaly_of_temperature
sea_surface_water__anomaly_of_geopotential_height
sea_surface_water__anomaly_of_temperature

• Before 3/19/13 this was treated as a quantity suffix, but now it is treated as an "operation prefix". It does not change the units. See Component, Increment and Magnitude.

• Means the "difference from climatology" in CF Standard Names. The "mean climatology" used as a reference should be specified in the Model Metadata File with an <assume> tag. See Reference Quantities.

• The word "anomaly" is used in 4 CF Standard Names, namely:

air_pressure_anomaly    
air_temperature_anomaly
geopotential_height_anomaly
surface_temperature_anomaly

Area

  base_quantity = "area"
  Examples of Specific Quantities:
  "surface_area"

  Examples

basin_outlet__total_contributing_area
channel_x-section__area
glacier_surface__area
lake_surface__area
sphere_surface__area

• This quantity can be defined for any polygon and has units of length squared.

• The quantity "surface_area" can be defined for a surface that lies above some planar domain. However, this is usually not what is meant by the term "area". For CSDMS Standard Names, use "surface_area" for this situation and "area" otherwise.

• Several different terms are used for the area of a drainage basin, such as "drainage area", "contributing area", "upstream contributing area", "total contributing area (TCA)" and "specific contributing area (SCA)". A drainage basin can be viewed as a polygon with a well-defined area. The terms "total contributing area" (TCA) and "specific contributing area" (SCA) are used in reference to the region that contributes flow to an arbitrary line segment placed perpendicular to the flow direction at some point in a landscape. SCA is then defined as TCA divided by the length of this segment.

• When "surface" is used in connection with a body of water or ice, it indicates the top of that body and the area is the map view area.

Aspect

  base_quantity = "angle"
  Examples of Specific Quantities:
  "aspect_angle"

  Examples

land_surface__aspect_angle

• "Aspect angle" is the azimuth angle of the opposite of the gradient vector of elevation. Recall that the gradient is a 2D vector that points in the direction of steepest downhill and which has a magnitude equal to the slope. (See slope). The opposite of the gradient vector is a vector that points in the opposite direction, or the the direction of steepest uphill. It is sometimes referred to as the antigradient. Aspect angle could therefore also be expressed as: "azimuth_angle_of_antigradient_of_elevation".

• See: Aspect and Slope.

Capacity

  base_quantity = "capacity"
  Examples of Specific Quantities:
  "anion_exchange_capacity" (used in soil physics)
  "cargo_capacity" (e.g. of an automobile)
  "cation_exchange_capacity" (used in soil physics)
  "carrying_capacity" (of an ecosystem)
  "infiltration_capacity" ####### (in hydrology; also called "infiltrability")
  "interception_capacity" (in hydrology)
  "isobaric_heat_capacity" (constant pressure) (of an entire object, extensive)
  "isochoric_heat_capacity" (constant volume) (of an entire object, extensive)
  "mass-specific_isobaric_heat_capacity" (constant pressure)
  "mass-specific_isochoric_heat_capacity" (constant volume)
  "volume-specific_isobaric_heat_capacity" (constant pressure)
  "volume-specific_isochoric_heat_capacity" (constant volume)

  Examples

air__volume-specific_isochoric_heat_capacity
anvil__isobaric_heat_capacity
aluminum__mass-specific_isobaric_heat_capacity
earth_human__carrying_capacity    (need to specify two objects)
space-shuttle_tile__isochoric_heat_capacity

• The word "capacity" indicates the maximum "amount" of something that an object can hold. When applied to an empty container, like a fuel tank, it has units of volume. However, it may also be a nonnegative integer, as in "carrying capacity" or have other units, as in various types of heat capacity.

• Heat capacity is an extensive property of an object (or matter); it is proportional to the amount of matter and can be used for discrete objects (like an anvil). There are two types of heat capacity, one computed with the pressure held constant, called "isobaric" and another with the volume held constant, called "isochoric". "Specific heat capacity" (often called "specific heat capacity") is an intensive property, that is, an amount per unit mass or volume. In the CSDMS Standard Names, the adjectives "mass-specific", "volume-specific" and "mole-specific" are used to remove ambiguity.

• "Thermal capacity" is another, but less commonly used term for "heat capacity".

• Aluminum, copper, cast iron and stainless steel cookware are often compared in terms of their thermal conductivity (how well they conduct heat) and heat capacity (how well they retain heat). See: Cookware and bakeware.

• The term carrying capacity follows the Process_name + Quantity Pattern and is the maximum population size for a given ecosystem.

• There are 4 CF Standard Names that contain "capacity", namely "soil_thermal_capacity" and 3 others that contain the phrase "at_field_capacity" and refer to soil moisture. The coresponding CSDMS standard name is: "soil_field_capacity_water_content". See the Soil template on the CSDMS Object Templates page for more information.

• See: Battery capacity, Cation-exchange capacity, Channel capacity, Combining capacity, Heat capacity and Tonnage.

Charge

  base_quantity = "charge" [C = Coulombs, SI unit]

  Examples

electron__electric_charge

• The total electric charge is a fundamental conserved quantity of an isolated system.

• Electric charge is quantized, that is, it comes in multiples of the the charge of an electron, called the elementary charge, denoted as "e". The charge of a quark is 1/3 of this value. Electric charge also carries a sign; protons and electrons have charges of e and -e.

• See: Electric charge and Elementary charge.

Circulation

  base_quantity = "circulation"

  Examples airfoil_curve~enclosing__circulation

• In fluid dynamics, circulation is the line integral of a velocity field around a closed curve. If not otherwise specified, that closed curve is taken to enclose the object in the object part of the name (i.e. in a CSDMS Standard Name). The closed curve is also assumed to lie wholly within the "potential flow" region and not in the boundary layer close to the boundary of the airfoil/object.

• We could also use something like: "airfoil" + "closed_line_integral_of_velocity"

• See: Circulation.

Code

  base_quantity = "code"

  Examples

basin__pfafstetter_code
basin__usgs_hydrologic_unit_code
location__postal_code     (See: Postal code.)

• For hydrologic features such as rivers, unique identification numbers such as the USGS Hydrologic Unit Code (or "HUC number") and Pfafstetter Code are used.

• Codes sometimes include both numbers and letters.

• See Number.

Coefficient

  base_quantity = "coefficient"
  Examples of Specific Quantities:
  "absorption_coefficient"
  "attenuation_coefficient"
  "diffusion_coefficient"
  "drag_coefficient"
  "eddy_diffusion_coefficient"
  "exchange_coefficient"
  "expansion_coefficient"
  "extinction_coefficient"
  "friction_coefficient"
  "lift_coefficient"
  "partition_coefficient"
  "reaeration_coefficient"
  "reflection_coefficient"
  "scattering_coefficient"
  "sieving_coefficient"
  "transfer_coefficient"
  "transmission_coefficient"

  Examples

airfoil__drag_coefficient
airfoil__lift_coefficient
concrete_rubber__kinetic_friction_coefficient
atmosphere_air_radiation__beer_lambert_law_attenuation_coefficient
iron__thermal_volume_expansion_coefficient
glacier__glen_law_coefficient
math__binomial_coefficient     (See Constants in Math)
pavement_rubber__static_friction_coefficient
polynomial__leading_coefficient
spring~steel__hooke_law_coefficient    [kg s-2]    (the "spring constant" in Hooke's law)
water_salt__diffusion_coefficient

• Coefficients are multiplicative factors that often occur in empirical laws, and other mathematical expressions. In the CSDMS Standard Names, other "control variables" that do not appear as multiplicative factors are referred to as parameters. (However, sometimes people refer to these other parameters as coefficients.) Coefficients and exponents can be viewed as special types of parameters. Parameters are typically not model state variables, but instead are "tunable" "control parameters" that define the model itself.

• Many quantity names (see above) are built from the base quantity "coefficient" and a process name, which conforms to the Process_name + Quantity Pattern.

• Diffusion is the process by which a substance moves (down gradient) from regions of high concentration to regions of low concentration. In molecular diffusion this process is driven by thermal energy. In turbulent diffusion it is driven by random fluctuations and swirling structures in the flow, such as eddies. When unqualified, a diffusion coefficient refers to the parameter, D, in the diffusion equation that has units of [m2 s-1], regardless of what substance is diffusing. The term eddy diffusion coefficient (also called "eddy diffusivity") is used for turbulent diffusion and also has units of [m2 s-1]. See the section for Diffusivity (which needs to be reconciled with this one).

• The concept of bulk parameterization is used in atmosphere and ocean science in order to estimate the rates (as fluxes) at which mass, momentum and heat are transferred between the atmosphere and the surface of either the land or sea. This approach uses the logarithmic law of the wall to relate the fluxes to values of heat, momentum, humidity (water vapor) or other gases that are measured at some fixed height above the interface (e.g. 10 meters). The use of the adjective "bulk" seems to stem partly from the idea of "bulk flow" (also called "free stream flow"), or flow that is far enough away from the interface boundary that it moves relatively unimpeded, as opposed to near-boundary flow. It also indicates that fluxes obtained by this method should be applicable over larger areas. Bulk transfer coefficients (also called "bulk exchange coefficients") are quantities associated with this approach, and can be defined somewhat differently by different authors, for example as dimensionless quantities or including shear velocity as a factor (with velocity units). There are separate bulk transfer coefficients for mass (water vapor or another gas, which may condense at the interface), momentum and heat. These bulk transfer coefficients are initially computed for a "neutral" state (e.g. when the surface temperature is equal to the air temperature), and then typically adjusted (e.g. by a function of bulk Richardson number) depending on whether the (stratified) atmosphere is in a "stable" (e.g. T_surf > T_air) or "unstable" (T_surf < T_air) state. These considerations lead to standard names such as "bulk_mass_transfer_coefficient" and "bulk_sensible_heat_transfer_coefficient" which are taken to be dimensionless. Note that the adjectives "stable" and "unstable" are not included because they are attributes of the atmosphere that are used to compute the bulk transfer coefficient but can change during a model run. The adjective "neutral" can be included, however, since this allows access to the "base value" that is modified for the stable and unstable cases. Note: The product of the wind speed at the reference height and a bulk transfer coefficient is sometimes called the "bulk aerodynamic conductance" (of mass, momentum or heat). The reciprocal is then the "bulk aerodynamic resistance".

• In the book, "Hydrology: An Introduction" by Brutsaert (2005, p. 41), the transfer coefficients for mass, momentum and heat are defined as dimensionless numbers and denoted as: Ce, Cd and Ch. Ce is also called the Dalton number (for water vapor). Cd is also called the drag coefficient. Ch is also called the Stanton number. However, this differs from other definitions; see: Heat transfer coefficient (SI units of [W m-2 K-1]) and Mass transfer coefficient (SI units of [m s-1]).

• The "Manning n parameter" is sometimes called "Manning's roughness coefficient" or "Manning's coefficient" or something similar. (But the word "roughness" is not needed to remove ambiguity.) Since Manning's n appears in the denominator of Manning's formula, it technically isn't a coefficient (i.e. its inverse is the multiplicative factor, or coefficient). Note that Manning's formula also contains another parameter, usually denoted by "k" that serves as a unit conversion factor. In the CSDMS Standard Names these are both referred to as "parameters" and use that pattern.

• The terms "attenuation_coefficient" and "attenuation_factor" are both used but they refer to different quantities associated with the Beer-Lambert Law. The "attenuation coefficient" is a parameter in the Beer-Lambert law with units of inverse length. When applied to gases in the atmosphere, dimensionless quantities called "optical air mass" and "optical depth" are instead used in the exponential. "Attenuation factor " is apparently a synonym for "transmittance", which is the ratio of transmitted to incident radiation, I(x)/I(0), a positive number less than 1. See: Absorbance, Air mass, Attenuation coefficient, Beer-Lambert Law, Optical depth and Transmittance.

• See: Attenuation coefficient, Ballistic coefficient, Binomial coefficient, Coefficient, Drag coefficient, Extinction coefficient, Friction, Heat transfer coefficient, Lift coefficient, Manning formula, Mass diffusivity, Mass transfer coefficient, Partition coefficient, Pressure coefficient, Reflection coefficient, Sieving coefficient, Skin friction coefficient, Thermal expansion and Transmission coefficient.

• See Constant, Exponent, Factor, Index, Number and Parameter.

• See Friction.

Component

  [ direction adjective(s) ] + "_component_of_" + [ vector quantity ]

  Examples

atmosphere_air_flow__east_component_of_velocity
atmosphere_air_flow__north_component_of_vorticity
channel_water_flow__x_component_of_velocity
sea_water_flow__down_east_component_of_stress

• Components of vectors and tensors are constructed using coordinate-direction adjectives and the "component_of" operation, as shown in the examples above.

• The coordinate-direction adjectives are: east, west, north, south, x, y, z, up, down, offshore, longshore, cross_stream and downstream. Two coordinate-direction adjectives are needed for a component of "flow_shear_stress". As of 7/28/14, eastward, westward, northward and southward have been shortened to east, west, north and south.

• Note that the word "flow" is used in the object part of the name as a shorthand for "flow_field". It is another example of the Object Name + Model Name Pattern.

• See Stress, Velocity and Vorticity.

• This was changed from a "quantity suffix" to a vector operation on 2/7/13. See CSDMS Operation Templates.

Compressibility

  base_quantity = "compressibility"
  Examples of Specific Quantities:
  "isentropic_compressibility"
  "isothermal_compressibility"

  Examples

atmosphere_air__isothermal_compressibility

• Compressibility is a measure of the relative change in volume in response to a pressure.

• See: Compressibility and Compressibility equation.

Concentration

  base_quantity = "concentration"
  Examples of Specific Quantities:
  "mass_concentration" [kg m-3]
  "molar_concentration" [mol m-3] (molarity)
  "number_concentration" [m-3]
  "volume_concentration" [1] = [m3 / m3]

  Examples

channel_water_sediment~suspended__mass_concentration
sea_water_magnesium-chloride__molar_concentration
sea_water_sediment~suspended__mass_concentration

• There are four main types of concentration, shown above, and they all have different units.

• The quantity "concentration" is always associated with two substances (objects) so we use the Object-in-object Quantity Pattern.

• Molality is a related concept with SI units of [mol kg-1].

• Mass fraction and mole fraction are both dimensionless ratios.

• Mass ratio and mole ratio are also dimensionless ratios and are considered "mixing ratios". See: Mixing ratio.

• "Molar concentration" is also called "molarity". See: Molarity.

• "Volume concentration" is also called "volume fraction". See Fraction.

• The term "osmotic concentration" is also used.

• See: "Mineral makeup of seawater".

• See: Concentration, Seawater and Sediment transport.

Conductance

  base_quantity = "conductance"
  Examples of Specific Quantities:
  "atmospheric_conductance" [m s-1]
  "bulk_atmospheric_conductance" [m s-1]
  "electrical_conductance" [A V-1]
  "fluid_conductance" [m2 s-1]
  "thermal_conductance"

  Examples

snow__thermal_conductance

• Conductance is the reciprocal of resistance.

• Conductance is different from conductivity. See Conductivity.

• The product of wind speed at a reference height and a bulk transfer coefficient is called the "bulk aerodynamic conductance" (of mass, momentum or heat). The reciprocal, "bulk aerodynamic resistance", is also used. See Coefficient.

• Units cannot be determined from the "base quantity" name as shown above.

• See: Electrical resistance and conductance, Fluid conductance and Thermal conductance.

Conductivity

  base_quantity = "conductivity"
  Examples of Specific Quantities:
  "electrical_conductivity" [siemens m-1] or [ohm-1 m-1]
  "hydraulic_conductivity" [m s-1]
  "ionic_conductivity"
  "thermal_conductivity" [W m-1 K-1] (this is an intensive property; don't need to add "specific")

  Examples

sea_water__electrical_conductivity
snow__thermal_conductivity
soil__saturated_hydraulic_conductivity

• Units cannot be determined from the "base quantity" name as shown above.

• Hydraulic conductivity can depend on coordinate direction unless the soil is assumed to be isotropic. When applicable, include an <assume> tag in the Model Metadata File with the standard assumption name: "isotropic_medium". See CSDMS Assumption Names for more information.

• "Relative hydraulic conductivity" is the ratio of (K / K_sat). See Smith (2002).

• See: Electrical conductivity, Hydraulic conductivity, Ionic conductivity and Thermal conductivity.

Constants in Math

  base_quantity = "constant"
  "math_" + constant_name + "_constant"

  Examples

math__catalan_constant
math__chaitin_constant
math__conway_constant
math__e_constant                (or math_euler_e_constant ??)
math__euler_gamma_constant
math__feigenbaum_alpha_constant
math__feigenbaum_delta_constant
math__golden_ratio_constant
math__googol_constant
math__khinchin_constant
math__pythagoras_constant   (= square root of 2)
math__sierpinski_constant
math__twin_prime_constant
math__pi_constant

• This includes numbers like "pi", "phi" and "e". See Wikipedia: Mathematical constant for a table with numerous examples.

• These numbers are not a quantity associated with an object like our others so we have used "math" as a placeholder object. Note that one model may want to check the number of significant digits of a math constant (like pi) that are used in another model, for example.

• phi = 1.61803... is known as the golden ratio.

• See the Dimensionless Number template.

Constants in Physics

  base_quantity = "constant"

  Examples

air__dielectric_constant  [1]            (can be complex)   
earth__solar_constant              [W m-2]        (solar_irradiation_constant may be better)
earth__standard_gravity_constant   [m s-2]  ("little g", see Attributes of Planets template)

physics__atomic_mass_constant    [kg]   (about 1.660538921e-27)
physics__avogadro_constant           [unit mol-1]   (see Note below)
physics__boltzmann_constant         (See ideal_gas_constant)
physics__cosmological_constant       [m-2]   (about 10^{-52};  object = universe)
physics__coulomb_constant            [N m2 C-2]     (C = Coulomb SI unit)   
physics__elementary_charge_constant    [C]    (charge of a proton and > 0; -1 times charge of an electron)   
physics__fine_structure_constant     [1]            (about 1/137.035999074)
physics__gravitational_coupling_constant     [1]        (about 1.7518e-45)
physics__hartree_energy_constant     [J]
physics__ideal_gas_constant          [J mol-1 K-1]   (R = 8.3144621)
physics__planck_constant             [J s]
physics__planck_mass_constant    [kg]  (about 2.17651e-8)
physics__radiation_constant    [J m-3 K-4]
physics__reduced_planck_constant
physics__rydberg_constant            [m-1]
physics__static_relative_permittivity
physics__stefan_boltzmann_constant   [W m-2 K-4]
physics__universal_gravitation_constant   [m3 kg-1 s-2]  ("big G", from Newton's law; or just "gravitational_constant")
physics__vacuum_electric_permittivity_constant   [F/m]  ("electric constant")
physics__vacuum_impedance_constant   [ohms]   (about 376.73031)
physics__vacuum_light_speed_constant        [m s-1]     (put "vacuum" in the object part ??)  ##########
physics__vacuum_magnetic_permeability_constant  [N A-2] or [H m-1]   ("magnetic constant")
physics__von_karman_constant         [1]

• If there is no naturally-associated object, the object name "physics" can be used as a placeholder object name. Or we could remove the object name requirement when the base quantity is "constant".

• Although "latent heat of fusion" and "latent heat of vaporization" are constants for a given substance (e.g. water), they have the following CSDMS standard names:

 water__mass-specific_latent_fusion_heat          (334 [kJ kg-1])
 water__mass-specific_latent_vaporization_heat    (2500 [kJ kg-1])

Note that "specific_latent_heat" is a quantity name so the quantity name part of these examples conforms to the Process_name + Quantity Pattern. See the template for Heat and Latent heat.

• The modern name for "Avogadro's number" is the "avogadro_constant". (See Avogadro constant.) It has units and is equal to: 6.02214129(27)x10^{23} [mol-1] or [unit mol-1]

• The speed of light depends on the medium it is traveling through. In a vacuum, v = c = 299,792,458 [m s-1]. In other materials, v = (c / n), where n > 1 is the refraction index. For visible light in air, n is about 1.0003. So an unambiguous standard name should indicate the medium and the wavelength range in the object name. Since the medium that the light is traveling through matters, we use the Object-in-object Quantity Pattern to create standard names such as: "visible_light_in_air_speed".

• The speed of light in a vacuum is a constant that is independent of wavelength. Perhaps we should give it the standard name "light_in_vacuum_speed_constant" which follows the Object-in-object Quantity Pattern.

• The "universal gravitational constant' appears in Newton's Law of Gravitation and is denoted as G (big G). It has units of [m3 kg-1 s-2]. The "Earth gravitational constant" is more correctly called the "Earth standard gravity constant". It is the average free-fall acceleration of Earth's gravitational field near the surface of the Earth and is denoted as g (little g). Even though it varies with position on Earth, it is defined to be precisely 9.80665 [m s-2] (an average value). See: Standard gravity and Gravity of Earth.

• While the coefficient in Hooke's law is often called the spring constant, we instead use 'spring~steel__hooke_law_coefficient for consistency with coefficients in other empirical laws.

• In meteorology, the ratio of the ideal gas constant, R, and the isobaric mass-specific heat capacity, cp, is called the Poisson constant. It is used in the definition of potential temperature.

• See: Boltzmann constant, Coulomb constant, Elementary charge, Fine-structure constant, Gravitational coupling constant, Ideal gas constant,Planck constant, Psychrometric constant,Rydberg constant, Stefan-Boltzmann constant, Universal gravitational constant, Vacuum electric permittivity, Vacuum magnetic permeability and von Karman constant.

• See: Physical constant.

Content

  base_quantity = "content"
  Examples of Specific Quantities:
  "cold_content"
  "energy_content"
  "mass_content"
  "volume_content"

  Examples

coal__thermal_energy_content
gasoline__thermal_energy_content
snowpack__cold_content  ?   (See Note below.)
wood~dry__thermal_energy_content  

• The word "content" refers to the "amount contained within". It is therefore naturally associated with two objects and the Object-in-object Quantity Pattern.

• In the CF Standard Names, the term "content" is taken to mean an "amount per unit area", usually determined as a z-integral from the bottom to the top of the atmosphere of a mass or volume fraction. (e.g. CF has "soil_moisture_content", "soil_moisture_content_at_field_capacity" and "soil_carbon_content".) However, in other contexts it means an amount per unit volume, as in the term "water_content" from infiltration theory, which is a volume fraction. See Water Content.

• While soil "water content" is a fairly standard term in hydrology (infiltration theory), the CSDMS Standard Names use "volume_fraction" instead since it is less ambiguous, provides the definition, applies equally well to other objects like clay and sand, and keeps the word "water" in the object part of the name. See Attributes of Soil at CSDMS Standard Name Examples. However, it might be better to retain the word "content" for easy recognition (since "water content" is so widely used, and then use "volume_content" and "mass_content" instead of "volume_fraction" and "mass_fraction". Sometimes the terms gravimetric water content and volumetric water content are also used.

• The quantity "thermal_energy_content" is used in the context of fuels like coal, gas and wood, to indicate the amount of useful energy that can be extracted.

• The quantity "cold_content" is used in snow hydrology to describe the "energy deficit" that must be overcome before melting starts to occur. It is expressed as energy per unit area [J m-2]. This deficit results in an observed time lag between when the temperature is raised above the melting point to when snow actually begins to melt. It involves the concept of "latent heat of fusion" -- the (originally mysterious) amount of heat energy that must be added to a solid material before there is any change in its temperature. (See: Latent heat. In the CF Standard Names, the term "thermal_energy_content_of_surface_snow" is used, apparently to mean "cold_content". However, a Google search on "thermal energy content of snow" only returns 2 hits, and these are from the CF names. Note that "cold_content" is negative and "thermal_energy_content" is typically positive.

• Many CF Standard Names contain the base quantity "content". The following list shows the number, in parentheses, or each use pattern:

carbon_content [kg m-2]   (14)
energy_content [J m-2]  (25)  e.g. "thermal_energy_content_of_surface_snow"
enthalpy_content [**********] (4)
heat_content [J m-2]  (2)
ice_content [kg m-2]  (2)
mass_content [kg m-2]   (235)
moisture_content [kg m-2] or [m]  (6)
number_content [m-2]  (7)
ozone_content [Pa] or [m]  (2)
soot_content [kg m-2]  (1)
sulfate_content [kg m-2]  (1)
vapor_content [kg m-2] (14)   (most are "tendencies")
water_content [kg m-2]  (16)

We may therefore have a conflict with "water_content" unless it is resolved by the object part.

Coordinate

  base_quantity = "coordinate"

  Examples

alongshore_coordinate (oriented along and based on a shoreline; similar to sigma coordinates)
cross-shore_coordinate (off-shore and on-shore directions)
 
cross-stream_coordinate (oriented along and based on a stream centerline)
streamwise_coordinate   (upstream and downstream directions)
 
east_coordinate  (for a model; if not same as longitude)
west_coordinate
north_coordinate (for a model;  if not same as latitude)
south_coordinate

r_coordinate    (Cylindrical and Spherical coordinates, with azimuth_angle and elevation_angle)
 
u_coordinate   (e.g. orthogonal curvilinear coordinate systems)
v_coordinate    (e.g. orthogonal curvilinear coordinate systems)
 
x_coordinate   (Cartesian coordinates)
y_coordinate   (Cartesian coordinates)
z_coordinate   (Cartesian coordinates)

• Note that Geographic coordinates use latitude (north-south coordinate), longitude (east-west coordinate) and elevation (vertical coordinate). These are treated as standard base quantity names in the CSDMS Standard Names. See: Geographic coordinates.

• For spherical coordinates, we would usually use "azimuth_angle" and "elevation_angle" instead of "theta_coordinate" and "phi_coordinate". But perhaps the latter should also be allowed.

• The terms "normal_coordinate" and "tangential_coordinate" are also used in some contexts.

• See: Barycentric coordinates (astronomy), Barycentric coordinates (for a triangle or other simplex), Canonical coordinates, Coordinate system, Fermi coordinates, Fractional coordinates (crystallography), Galilean transformation, Generalized coordinates, Isothermal coordinates, Normal coordinates (from differential geometry) and Sigma coordinate system (also called terrain-following).

• See the section for Components above, where the same prefixes are used. In fact, instead of using "coordinate" as a base quantity, it would be possible to use "position", which is a vector quantity, similar to velocity. Then we could use "x_component_of_position" instead of "x_coordinate", etc. just as we use "x_component_of_velocity". Note that while the components of a position vector are called "coordinates", there is no similar, short term for the components of a velocity vector.

Correlation

  base_quantity = "correlation"

  Examples

(None yet)

• Note that correlations require two quantities to be specified, which is similar to certain other quantities such as Partial Pressure and Solubility.

• Although the Guidelines for Constructing CF Standard Names includes a provision for correlations as the transformation pattern: "correlation_of_X-and-Y_over_Z", there are currently no examples of CF Standard Names that contain "correlation". The same is true for "covariance" and "convergence". There are only three names with "divergence".

Count

  base_quantity = "count"
  Examples of Specific Quantities:
  "count-per-volume"

  Examples

basin_rain-gauge__count
human_blood_cell~platelet__count-per-volume   [count / microliter]
human_blood_cell~red__count-per-volume
human_blood_cell~white__count-per-volume
lake_water_fish_sample__count
mars_moon__count
model_grid_column__count

• This quantity name is sometimes used when the attribute being quantified can only take integer values, as in the examples above.

• In the case of blood cell counts, the units are usually a number per volume (e.g. number per microliter). See: Blood cell count. Once units are specified (e.g. in a Model Coupling Metadata (MCM) file), then "count-per-volume" is unambiguous. Is a platelet technically considered to be a type of blood cell?

• The "Wolman pebble count" due to M. Gordon "Reds" Wolman is sometimes used in river hydraulics and sediment transport. However, the goal of this procedure is to estimate the mean diameter of the pebbles on the stream bed, so the actual "count" (usually 100) is not of primary interest.

• The "diatom count" of a sample may be another example; are the units then the same as "abundance"? (e.g. "sediment_core_diatom_relative_abundance" ?)

• The number of occurrences of a given event may also be called a "count". (e.g. Geiger counters)

• See Count data and the Number template.

Current

  base_quantity = "current"
  Examples of Specific Quantities:
  "electrical_current"

  Examples

None yet.

• An electric current is a flow of charge, with an SI unit of "amperes" (i.e. "coulombs per second").

• See: Electric current.

Curvature

  base_quantity = "curvature"
  Examples of Specific Quantities:
  "gaussian_curvature"
  "mean_curvature"
  "max_normal_curvature" (a principle curvature)
  "min_normal_curvature" (a principle curvature)
  "plan_curvature"
  "profile_curvature"
  "streamline_curvature"
  "tangential_curvature"

  Examples

land_surface__plan_curvature
land_surface__profile_curvature

• Curvatures can be defined for surfaces that are twice-differentiable. In reality, natural surfaces are rough but they can be approximated as twice-differentiable surfaces.

• Plan curvature (or "contour curvature"), profile curvature and streamline curvature are used in geomorphometry, the analysis of land surfaces or topography.

• See Attributes of Topography and Attributes of Oceans on the Examples page.

• Curvature can also be defined for curves, such as coastline curves and space curves (or trajectories).

• See: Curvature, Geomorphometry and Radius of curvature.

Density

  base_quantity = "density"
  Examples of Specific Quantities:
  "bits-per-area_density"
  "bulk_mass-per-volume_density"
  "charge-per-area_density"
  "energy-per-area_density" [J m-2]
  "energy-per-volume_density" [J m-3]
  "length-per-area_density" [m-1]
  "mass-per-area_density" [kg m-2]
  "mass-per-volume_density" [kg m-3]
  "number-per-area_density" [m-2]
  "number-per-volume_density" [m-3]
  "particle_mass-per-volume_density"
  "torque-per-volume_density" [N m / m-3] = [N m-2]

  Examples

atmosphere_air__mass-per-volume_density
atmosphere_air__mass-per-volume_density  (stp = standard temperature and pressure)
basin_channels__total-length-per-area_density   (known as "drainage_density")
universe~friedmann__critical_density
sea_water__mass-per-volume_density

• The word density usually refers to the amount of something within a fixed amount of space. The "amount of space" could be 1D (line), 2D (area) or 3D (volume). For greater clarity (and to avoid ambiguity), standard quantity names like mass-per-volume_density and the others listed above are used in the CSDMS Standard Names. Similar issues occur for Concentration (see section by that name). Also see the section for Flux.

• The quantity name Bulk density refers to the mass of many particles (e.g. sediment grains) divided by the volume that they occupy. For clarity, here we use "bulk_mass-per-volume_density".

• Column density is a type of area density defined as the z integral of a volume fraction from the bottom to the top of a column of water or air, as in the ocean or atmosphere. In the CF names, the quantity name "content" is used for this concept. In the context of sediment plumes, the quantity name "sediment inventory" is used for this concept (a z-integral over the depth of a freshwater plume entering the sea).

• Physicists sometimes use the term "flux_density".

• Hydrologists use the term "drainage_density", which is defined as the total length of channels in a drainage basin divided by the drainage area. Generic units are therefore inverse length. Similarly, "source_density" can refer to the total number of sources (i.e. channel heads) in a basin divided by the drainage area.

• Other valid quantities include "current_density", "electron_density" (in plasma physics), "thermal_energy_density" and "magnetic_energy_density".

• See: Area density, Column density, Bulk density, Critical density,Current density, Density, Drainage density, Electron density, Energy density, Knot density, Linear density, Memory storage density, Number density, Orthobaric density, Particle density, Population density, Potential density, Power density, Probability density function, Relative density, Surface power density, Torque density and Vapour density.

Depth

  base_quantity = "depth"
  Examples of Specific Quantities:
  "secchi_depth"

  Examples

channel_water__mean_depth
sea_water__secchi_depth
sea_water_below-surface__depth
sea_water_bottom__depth
soil_sat-zone_top__depth    ##### (or if not soil, land_subsurface_sat-zone_top__depth).

• Measured as a positive downward distance below a reference surface. In this sense, it is the opposite of "height" which is measured positive upward from a reference surface.

• CF Standard Names often use "thickness" instead of "depth". See the template for Thickness.

• The words "depth" and "thickness" are sometimes used interchangeably. In the context of "layers", "thickness" is usually used (e.g. in meteorology, geology and hydrogeology). In the context of surface water or snow, "depth" is usually used. (As in: "How deep is the lake?" or "The lake depth is 5 meters.") The word "depth" indicates a value that is positive downward from some reference datum, and which may take values less than some maximum possible value.

• Note that "secchi_depth" is a standard term that measures turbidity using a "visible depth". See: Secchi disk.

• While the term "precipitable_water_content" is commonly used, its units of length are not really consistent with the base quantity "content". The terms "precipitable water depth" and "precipitable depth of water vapor" are also used and imply units of length, but not all of the water can actually "precipitate". An unambiguous and currently-used standard name for this quantity is: "atmosphere_water~vapor" + "z_integral_from_bottom-to-top_of_volume_fraction".

• See Altitude, Elevation, Height and Thickness.

Diameter

  base_quantity = "diameter"

  Examples

basin_channel-network_graph__diameter
graph~tree~rooted__diameter
tree~oak~bluejack_trunk__diameter
impact-crater_circle__diameter      (see Object_name + model_name Pattern)
square__diameter

• This quantity usually has units of length (except for rooted tree graphs).

• Although often associated with a circle, the general definition of diameter is the maximum distance (for some metric) between any two points in a set. So any bounded geometric shape (e.g. a square or any polygon) has a well-defined diameter, as does any bounded set of points. Note that the diameter of a bounded set is the same as the diameter of its convex hull. In graph theory, the diameter of a rooted tree graph is the maximum number of edges between the root and any leaf. River networks have a well-defined diameter (though topological vs. geometrical) since they can be viewed as rooted tree graphs (rooted at the outlet).

• See Perimeter.

Diffusivity

  base_quantity = "diffusivity"
  Examples of Specific Quantities:
  "magnetic_diffusivity" [m2 s-1]
  "mass_diffusivity" [m2 s-1]
  "momentum_diffusivity" [m2 s-1] (nickname for kinematic_viscosity)
  "thermal_diffusivity" [m2 s-1]

• It appears that the units are always [m2 s-1].

• "thermal_diffusivity" seems preferable to "heat_diffusivity"

• Common adjectives are: biharmonic, laplacian, epineutral, etc.

• The term "eddy diffusivity" is sometimes used as a synonym for the "eddy diffusion coefficient", usually denoted as "K". See: Eddy diffusion.

• See: Magnetic diffusivity, Mass diffusivity, Kinematic viscosity, Momentum diffusion, Thermal diffusivity and Thermal conduction.

Dimension

  base_quantity = "dimension"
  Examples of Specific Quantities:
  "box_counting_dimension"
  "hausdorff_dimension"

  Examples

cantor-set__hausdorff_dimension
peano-curve__hausdorff_dimension
sierpinski-gasket__hausdorff_dimension

• This quantity is usually used in connection with fractals and it can be measured (usually using the box-counting dimension) for many objects in nature.

• See: Box-counting dimension, Dimension, Fractal dimension, Hausdorff dimension and Packing dimension.

Dimensionless Numbers

  [ famous person's name ] + "_number"

  Examples

air_helium-plume__richardson_number
airplane__mach_number
channel_water_flow__froude_number
channel_water_flow__reynolds_number
equation~heat__courant_number   #### (insert "model" ??)
ship__froude_number

• Dimensionless numbers are widely used in physics and typically obtained as the ratio of two quantities that have the same units. For example, Reynolds number gives the ratio of inertial and viscous forces in a flow problem, and flows transition from laminar to turbulent as the Reynolds number increases.

• Wikipedia has a nice table of dimensionless numbers which provides numerous examples.

• Some names, like "Reynolds", end in "s", but a possessive "s" is not added at the end. See the CSDMS Standard Name Basic Rules.

• The modern name for "Avogadro's number" is the "Avogadro constant" and it is not dimensionless.

• See the Attributes of Atoms and Number templates for terms like "proton_number".

• See the Number template for more information.

Discharge or Volume Flow Rate

  "volume_flow_rate"
  Examples of Specific Quantities:
  "volume-per-unit-contour-length_flow_rate" (or per-unit-length ??)

  Examples

channel_water_x-section__volume_flow_rate [m3 s-1]
lake_water~incoming__volume_flow_rate [m3 s-1]
lake_water~outgoing__volume_flow_rate [m3 s-1]

• The term "discharge" is used primarily by hydrologists and is commonly denoted as "Q". The term "volume_flow_rate" is more broadly understood.

• The term "discharge" has the connotation of something leaving a domain, so additional clarification is generally needed to indicate whether the volume flow rate is into or out of a given domain (e.g. with "incoming" or "outgoing"). The quantity names incoming_volume_flow_rate and outgoing_volume_flow_rate are always unambiguous.

• Hydrologists also use "unit_width_discharge" (discharge per unit contour width) in the context of surface flows. It is usually denoted by lower-case "q" and has SI units of [m2 s-1]. Here we use "volume-per-unit-length_flow_rate" instead. Note that this may also be used for the "lateral inflow rate" to the sides of a channel as in: "channel_bank_water__volume-per-unit-length_flow_rate".

• See: Discharge, Volumetric flow rate, Volumetric flux and Mass flow rate.

• A "volume_flux" has units of [m3 m-2 s-1] = [m s-1], as in Darcy's Law. Discharge is then the integral of a volume flux over the cross-sectional area of a channel or pipe. See the Flux template.

• Avoid "streamflow" and "outflow" as synonyms for "discharge" or else define them to be aliases.

• If a "sediment discharge" quantity has units of [mass / time], then it should be called something like "channel_water_sediment~suspended" + "mass_flow_rate" instead of "channel_water_sediment~suspended" + "volume_flow_rate", since discharge has units of [volume / time].

• See the Flow Rate template.

Distance

  base_quantity = "distance"
  Examples of Specific Quantities:
  "average_distance"
  "separation_distance"

  Examples

channel_centerline_endpoints__separation_distance 
earth-to-sun__average_distance

• This quantity seems to require specifying two objects, just as solubility, partial_pressure and volume_fraction do. In the latter cases the special keyword "_in_" was introduced. Here the reserved word "-to-" and the pattern: (object + "-to-" + object + distance) is used in a similar way. The keyword "-to-" can also be used for ratios. See "Ratios".

• We could introduce "straight_distance" as a synonym for euclidean_distance or just use the latter term. Or perhaps use "euclidean_length" instead?

• The word "distance" is sometimes used in a more abstract sense, as a measure of dissimilarity between two objects. For example, the Hamming distance measures the dissimilarity of two text strings. See: Metric, Distance, Euclidean distance, Uniform norm and Taxicab geometry (or "Manhattan distance").

Duration

  base_quantity = "duration"
  Examples of Specific Quantities:
  [process name] + "_duration" (e.g. exposure_duration, precipitation_duration)

  Examples

aircraft__flight_duration
atmosphere_water__precipitation_duration  (vs. "rainfall duration")
earth_day~sidereal__duration
earth_day~solar-mean__duration
earth_day~stellar__duration
land_surface__sunshine_duration       (or "daylight_duration")
water_scuba-diver__dive_duration

• Used to indicate a time period.

• See the Precipitation section.

• Typically preceded by a process name modifier. See CSDMS Process Names for a list of process names.

Efficiency

  base_quantity = "efficiency"
  Examples of Specific Quantities:
  "electrical_efficiency"
  "luminous_efficiency"
  "mechanical_efficiency"
  "thermal_efficiency"

  Examples

engine__thermal_efficiency

• Efficiency is usually expressed as a ratio of what is achieved to the max possible (or ideal) value and is therefore a dimensionless number.

• See: Carnot heat engine, Electrical efficiency, Energy conversion efficiency, Fuel efficiency, Luminous efficiency, Mechanical advantage, Mechanical efficiency and Thermal efficiency.

Elevation

  base_quantity = "elevation"

  Examples

bedrock_surface__elevation
land_subsurface_sat-zone_top__elevation   (vs. ground_water-table_surface)  ####
land_surface__elevation
sea_water_surface__elevation

• There is a subtle but important difference between the quantities "altitude" and "elevation". The word altitude refers to the distance of an object (e.g. aircraft, air parcel or balloon) above the ground, regardless of the local elevation of the land surface. The word elevation refers to the distance of an object (typically a land surface) above a datum, such as the mean sea level datum. Elevation is one of the three Geographic coordinates used to specify a 3D location (i.e. elevation, latitude and longitude).

• See the quantity templates for Altitude, Depth, Height, Thickness.

• See the object template for Surface. Elevation is one of many attributes that can be associated with a surface.

• See Reference Quantities.

Emissivity

  base_quantity = "emissivity"

  Examples

land_surface__emissivity

• Emissivity is a measure of the effectiveness of a surface in emitting energy as thermal radiation (also called "longwave radiation"). It is defined as the (dimensionless) ratio of the thermal radiation emitted by a surface/object and the thermal radiation that would be emitted by an ideal black body surface at the same temperature.

• Emissivity values are dimensionless and range between 0 and 1.

• See: Black body, Black-body radiation, Earth's energy budget, Emissivity, Outgoing longwave radiation and Shortwave radiation.

Emittance

  base_quantity = "emittance"

  Examples

land_surface_radiation~incoming~longwave__emittance

• Emittance is the energy flux emitted by a source, and has SI units of [W m-2] or [J m-2 s-1].

• See: Irradiance.

• See: Absorbance, Attenuation coefficient, Beer-Lambert law, Mass attenuation coefficient, Opacity (optics), Reflectance and Transmittance.

Energy

  base_quantity = "energy"
  Examples of Specific Quantities:
  "electric_energy"
  "free_energy"
  "internal_energy"
  "kinetic_energy"
  "potential_energy"
  "specific_energy"
  "thermal_energy"

  Examples

projectile__potential_energy
water__gibbs_free_energy

• The SI unit for energy is Joules.

• Specific energy is energy per unit volume or mass.

• Some possible forms of energy are thermal, chemical, radiant, nuclear, magnetic, elastic sound, mechanical, luminous and mass. See Energy.

• See Gibbs free energy, Helmholtz free energy and Thermodynamic free energy.

Exponent

  base_quantity = "exponent"

  Examples

basin__flint_law_exponent
basin_channel~longest__hack_law_exponent
channel_water_sediment~suspended__volume_flow_rate_law_area_exponent
glacier__glen_law_exponent

• Exponents often occur in empirical laws.

• Systems that can undergo phase transitions are often characterized by a critical exponent.

• See Coefficient, Constant, Factor, Index, Number and Parameter.

Factor

  base_quantity = "factor"

  Examples

oscillator__q_factor
pipe_water_flow__darcy_friction_factor  (same as moody_friction_factor)
pipe_water_flow__fanning_friction_factor
sun-lotion_skin__protection_factor  (known as SPF)
wave~sine__crest_factor

• Use "manning_n_parameter" instead of "manning_friction_factor".

• Many different types of Shape factor are used in image analysis, such as the "circularity_shape_factor", "elongation_shape_factor", "compactness_shape_factor" and "waviness_shape_factor".

• Another type of shape factor is given by the square root of area divided by the shape's diameter (max distance between any 2 boundary points.).

• A model may use an "adjustment_factor", "correction_factor" or "compensation_factor".

• See: Atomic form factor (or atomic scattering factor), Crest factor, Cunningham correction factor (for small particles in a fluid), Q factor, Sun Protection Factor (SPF) and View factor.

• See Coefficient, Constant, Exponent, Index, Number and Parameter.

Flag

  base_quantity = "flag"

  Examples

model__**_option_flag

• We may want to allow "flag" as a quantity since many models provide options as boolean values known as "flags". It isn't clear yet, however, how these would be shared between models or what the object_name would be.

• See Flag (computing).

Flow Rate

  base_quantity = "flow_rate"
  Examples of Specific Quantities:
  "mass_flow_rate"
  "momentum_flow_rate"
  "energy_flow_rate"
  "volume_flow_rate"
  "mole_flow_rate"

  Examples

channel_entrance_water_x-section__volume_flow_rate
channel_exit_water_x-section_sediment~suspended__mass_flow_rate
lake_water~incoming__volume_flow_rate

• The quantity name "flow_rate" can be ambiguous in the context of a fluid that can either flow into or out of the object in the object part of the name. In such cases, the process names "inflow" and "outflow" can be used instead of "flow" and are viewed relative to the object. While "discharge" is commonly used as a quantity name in hydrology, it connotes a volume outflow rate and sounds strange when used to refer to a volume inflow.

• The base quantity "rate" implies that units of inverse time are added to the units of the quantity that is being transported. For example, in SI units we have:

mass_flow_rate       [ kg s-1 ]
momentum_flow_rate   [ kg m s-2 ]
energy_flow_rate     [ J s-1 ] = [ W ]
volume_flow_rate     [ m3 s-1 ]
mole_flow_rate       [ mol s-1 ]

• "Energy flow rate" is also known as "power". See: Power.

• See: Discharge, Volumetric flow rate and Mass flow rate.

• See the templates for Discharge, Flux and Rate of a Process.

Flux

  base_quantity = "flux"
  Examples of Specific Quantities:
  "mass_flux"
  "momentum_flux"
  "energy_flux"
  "volume_flux"
  "mole_flux" (perhaps this should be "number_flux" to be independent of units.)
  process_name + "_flux"   (e.g. "radiation_flux")

  Examples

land_surface_radiation~outgoing~longwave__energy_flux       (emitted and upward)
land_surface_radiation~incoming~longwave__energy_flux       (incident and downward)

• See the section on Radiation on the CSDMS Quantity Templates page for many examples of radiation fluxes.

• In the context of "transport phenomena", the definition of "flux" is flow rate per unit area. In addition to the phrase "per unit area", this definition includes the word rate which implies per unit time. So the base quantity "flux" implies that units of [m-2 s-1] are added to the units of the quantity that is being transported. For example, in SI units we have:

mass_flux        [ kg m-2 s-1 ]
momentum_flux    [ kg m s-1 m-2 s-1 ]  = [ kg m-1 s-2 ] = [ Pa ]      (force per unit area, same units as "pressure")
energy_flux      [ W m-2 ] = [ J m-2 s-1 ]
volume_flux      [ m s-1]  = [ m3 m-2 s-1 ]
mole_flux        [ mol m-2 s-1 ]

• "Flux" can also be understood as "surface bombardment rate".

• "Flow rate" is the total amount of the transported quantity per unit time, or the product of an area and a flux. Replacing "flux" with "flow_rate" in a quantity name results in a different, but also valid quantity.

• The examples above show how the object name can be either a surface or a medium. Either type of object can potentially "absorb", "emit", "reflect" or "transmit" a flux.

• An energy flux emitted by an object is a quantity called outgoing_radiation_flux (positive if outgoing). An energy flux that is received by or incident on an object is a quantity called incoming_radiation_flux (positive if incoming). That is, the sun "radiates" energy and the earth is "irradiated" by this energy. This distinction means that "incident_radiation" serves as a synonym for "irradiation" and "emitted_radiation" as a synonym for "radiation". Some objects, like a land surface, can radiate longwave energy or be irradiated by longwave energy. In such cases, the term "outgoing_radiation_flux" establishes a sign convention that "outgoing is positive". Similarly, "incoming_radiation_flux" implies "incoming is positive". Process names often occur in pairs that indicate "incoming" or "outgoing", such as "emigration" and "immigration" or "exporting" and "importing". Note that a process name, like "radiation" represents an action that applies to the object in the object name part.

• The shortwave radiation incident on the land surface is typically modeled as the sum of three components, called direct, diffuse and backscattered. Only the "direct" component (radiation from the sun, transmitted directly through the atmosphere to the surface) is dependent on topographic slope and aspect. The other two are emitted (via reflections from aerosols) isotropically by the atmosphere so they appear to be arriving from a direction that is parallel to the local surface normal. For the "direct" component, an extra adjective like "slope_corrected" may be needed. See: Earth's radiation balance.

• A process name frequently precedes the base quantity "flux" in accordance with the Process_name + Quantity Pattern. Examples include "evaporation_volume_flux", "precipitation_mass_flux".

• It turns out that stress and momentum flux both have the same units of Pascals (or N m-2, or kg m-1 s-2). When a fluid exerts a shear stress on a boundary, this results in a momentum flux into the boundary and this loss of momentum slows the flow.

• What about "luminous flux" (for visible light)? See: Luminous flux.

• See: Flux, Transport phenomena.

• "Discharge" is a volume flow rate and not a flux. See Discharge.

• "momentum_diffusivity" [m2 s-1] is a nickname for kinematic_viscosity

• In the CF Standard Names, "flux" may be preceded by the words:
  mass, momentum,
  energy, heat, longwave, shortwave, radiative,
  water, vapor, evaporation,
  palm, photon, mole, salt
  Units are [W m-2] for the "energy fluxes" such as: "heat", "longwave", "shortwave" and "radiative". In addition, "shortwave_radiation" is abbreviated to "shortwave".

• See the templates for Concentration, Discharge and Flow Rate.

Fraction

  quantity_suffix = "fraction"
  Examples of Specific Quantities:
  "area_fraction"
  "mass_fraction"
  "mole_fraction"
  "time_fraction"
  "volume_fraction"

  Examples

basin_land~forested__area_fraction
basin_land~grassland__area_fraction
  
earth_surface_land__area_fraction
earth_surface_water__area_fraction
 # surface of a 3D region vs. mathematical surface
 
region_state_land~agricultural__area_fraction
region_state_land~arable__area_fraction
region_state_land~burned__area_fraction
region_state_land~cloud-covered__area_fraction
region_state_land~commercial__area_fraction
region_state_land~dry__area_fraction
region_state_land~farmed__area_fraction
region_state_land~flooded__area_fraction
region_state_land~flooded__max_of_depth   ####
region_state_land~forested__area_fraction
region_state_land~grassland__area_fraction
region_state_land~grazing__area_fraction
region_state_land~ice-covered__area_fraction
region_state_land~irrigated__area_fraction
region_state_land~lake-covered__area_fraction
region_state_land~water-covered__area_fraction
region_state_land~parkland__area_fraction
region_state_land~private__area_fraction
region_state_land~public__area_fraction
region_state_land~residential__area_fraction
region_state_land~snow-covered__area_fraction
region_state_land~urban__area_fraction
region_state_land~vegetated__area_fraction
region_state_land~wetland_fraction
 
rocket_payload__mass_fraction
rocket_propellant__mass_fraction  (See: Propellant mass fraction.)
    
sea_water_oxygen__volume_fraction
   
soil_air__volume_fraction     (Object-in-Object Pattern)
soil_clay__volume_fraction
soil_ice__volume_fraction
soil_loam__volume_fraction
soil_sand__volume_fraction
soil_silt__volume_fraction
soil_water__volume_fraction    (instead of "soil" + "water_content")  #####

• The word "fraction" can be viewed as a "quantity suffix" (as defined at the top) that can be applied to any base quantity (e.g. area, mass, mole, time, volume) to create a new quantity. In most (if not all) cases it is dimensionless.

• In order for "area_fraction" and "volume_fraction" to be well-defined, the object part of the name should ideally refer to a 2D or 3D shape (e.g. polygon or polytope) for which the area or volume can be computed. (e.g. for 2D, a state or a drainage basin)

• If an "area fraction" variable name is used with gridded data, then the "area_fraction" applies to the area of the grid cell. If the area fraction applies to some specific domain or object, such as a U.S. state or a drainage basin, then constructions like: "basin_land~forested + area_fraction" can be used and conform to the Part of Another Object Pattern.

• The quantity area_fraction is often used in connection with the fraction of land (in map or plan view) that meets some criteria. Adjectives like "burned", "forested", "public" and "urban" can be used to define the criteria as shown in the examples. As of 7/23/14, hyphenated adjectives like "snow-covered" are allowed.

• If an "area fraction" variable name is meant to distinguish between two possible states, such as land and water, then a reserved word like "vs" (or "to") could be used in a construction like: "land-vs-water + area_fraction".

• Variable names with "volume fraction" usually use the Object-in-object Quantity Pattern as in the examples.

• In the CF Standard Names, "fraction" is used in 306 names to form the following 5 quantities where the number of occurrences is indicated in parentheses:

area_fraction (19)
mass_fraction (179)
mole_fraction (95)
time_fraction (2)
volume_fraction (11)

The ones for "volume_fraction" fall into 5 groups:

ocean_volume_fraction
volume_fraction_of_oxygen_in_sea_water
volume_fraction_of_[clay, silt or sand]_in_soil
volume_fraction_of_condensed_water_in_soil + [assumptions]
volume_fraction_of_frozen_water_in_soil 

Hydrologists typically use the shorter term "soil_water_content" instead of "volume_fraction_of_condensed_water_in_soil". However, using "soil_water~condensed + volume_fraction" instead is consistent with the Object-in-object Quantity Pattern.

Frequency

  base_quantity = "frequency" [1/second] (but the meaning is "cycles per second")

  Examples of Specific Quantities:
  "angular_frequency" [radians/second]
  "nyquist_frequency" [1/second]

  Examples

cesium_atom__characteristic_emission_frequency
sea_water__brunt_vaisala_frequency   (also called "buoyancy_frequency")
sea_surface_water_wave__frequency

• Units of frequency are usually hertz = [1/second].

• Note that the word "frequency" alone means temporal frequency and "wavenumber" means spatial frequency. Note that "angular_frequency" is distinct from "frequency" and "angular_wavenumber" is distinct from "wavenumber", but they are closely related quantities.

• For periodic waves, the frequency is equal to the phase velocity divided by the wavelength. See the Period and Wavelength templates.

• See Angular frequency, Brunt–Väisälä frequency, Frequency, Normalized frequency and Nyquist frequency.

Friction

• Friction is not a quantity and is really a force as opposed to a process. It is not included in this list of CSDMS Process Names because it doesn't fit the general verb-to-noun process name pattern explained on that page. The word "traction" has similar issues.

• The adjective "frictional" is used in terms like "frictional_momentum_loss_rate". But the net loss of momentum (per unit time and per unit area) due to friction in a fluid is equivalent to the shear stress. Note that both have units [M L T-2]. See the template for Stress.

• Some quantities associated with friction are:

kinetic_friction_coefficient   (See the Coefficient template.)
log_law_roughness_length   ("z0" for law of the wall)
manning_n_parameter

shear_stress   (See the Stress template.)
static_friction_coefficient

• A Google search indicates that "friction_rate" is sometimes used in connection with air ducts.

Fuel Efficiency

  Examples of Specific Quantities:
  "fuel_consumption_rate" ["gallons per mile" or "liters per km"]
  "fuel_economy" ["miles per gallon" or "km per liter"]
  "fuel_specific_energy_content" [Joules / kg]

  Examples

automobile_fuel__consumption_rate
automobile_fuel__economy
automobile_fuel__specific_energy_content   (or energy-per-mass_content ??) #####

• In everyday language, the term "miles_per_gallon" is often used as if it were a quantity name but it is really a units name. "mileage" has various meanings and is not a well-defined quantity name.

• Is there a good "process - rate" quantity name for "fuel_economy" ? We could potentially replace "economy" with "per_gallon_miles".

• energy_efficiency and energy_intensity are related quantities.

• Efficiency of electric vehicles is often given as "cents_per_mile" which allows comparison to gas-powered vehicles.

• See: Fuel efficiency of vehicles and Efficient energy use.

Hardness

  base_quantity = "hardness"
  Examples of Specific Quantities:
  "indentation_hardness"
  "rebound_hardness"
  "scratch_hardness"

  Examples

snowpack_surface__indentation_hardness

• Hardness is a function of many things and there are 3 main types of hardness measurements called indentation hardness, rebound hardness and scratch hardness.

• See Hardness and Scratch hardness.

• The word hardness is also used in chemistry, in the context of "hard water". See: Carbonate hardness and Hard water. Permanent hardness is defined as Calcium hardness + Magnesium hardness, while temporary hardness is a synonym for Carbonate hardness. Water hardness can be measured as a molar concentration of calcium and magnesium ions, but several alternate units are used around the world and there are conversion factors between them.

Head

  base_quantity = "head"
  Examples of Specific Quantities:
  "friction_head"
  "hydraulic_head"
  "pressure_head"
  "velocity_head"

  Examples

pump__hydraulic_head
soil_water__pressure_head

• Head is a quantity used in fluid dynamics (hydraulics) that relates the energy in an incompressible fluid to the an equivalent height in a column of fluid. It has units of length.

• "Total hydraulic head" is the sum of the elevation head and pressure head.

• The "hydraulic_gradient" is computed by taking differences or derivatives of head values and determines the direction of fluid flow.

• See: Hydraulic head, Pressure head and Total hydraulic head.

Heat

  base_quantity = "heat"
  Examples of Specific Quantities:
  "mass-specific_fusion_latent_heat"
  "sensible_heat"

  Examples

water__mass-specific_latent_fusion_heat          (334 [kJ kg-1])
water__mass-specific_latent_sublimation_heat
water__mass-specific_latent_vaporization_heat    (2500 [kJ kg-1])

• The quantity "heat" refers to "thermal energy" that is being transferred from one system to another by thermal interaction. It has SI units of Joules.

• The word "specific" is often inserted as in "specific_latent_heat" and "specific_sensible_heat" to indicate thermal energy per unit mass [J kg-1].

• While the "latent heat of fusion" and "latent heat of vaporization" are constants for a given substance (e.g. water), they don't use the Constant template but are treated as in the two examples above in accordance with the Process_name + Quantity Pattern. Note that "latent_heat" is a quantity name and "fusion" and "vaporization" are process names.

• The quantities "advection_heat_flux", "conduction_heat_flux", "latent_heat_flux" and "sensible_heat_flux" are also used.

• See: Heat, Latent heat, Sensible heat and Thermodynamic databases for pure substances.

• See Energy and Flux of Heat or Energy.

Height

  base_quantity = "height"
  Examples of Specific Quantities:
  "geopotential_height"
  "reference_height"

  Examples

building~empire-state__height
human__mean_height
tree~oak~bluejack__mean_height

• See Geopotential height, Geostrophic wind and Above mean sea level.

• See Reference Quantities.

Humidity and Relative Saturation

  base_quantity = "humidity"
  Examples of Specific Quantities:
  "absolute_humidity" (is "volumetric_humidity" a synonym ?)
  "relative_humidity"
  "relative_saturation"
  "specific_humidity"

  Examples

atmosphere_air_carbon-dioxide__relative_saturation   ## CHECK
atmosphere_air_water~vapor__relative_saturation  (instead of air_relative_humidity)

• Relative humidity is a dimensionless ratio of partial pressures. It is defined as the ratio of the partial pressure of water vapor in the air-water mixture (often called the "vapor pressure") to the saturated vapor (partial) pressure of the water at a prescribed temperature.

• The relative humidity is often known (measured) and empirical equations for computing saturated vapor pressure as a function of temperature have been given by both Brutsaert and Satterlund. From these, vapor pressure can be computed from the definition.

• Relative humidity of air depends on both temperature and pressure.

• The more general term for relative humidity (when not talking about water vapor in air) is relative_saturation. It is the ratio of the partial pressure to the saturated partial pressure of one (condensable phase) gas in another (non-condensable phase) gas mixture.

Impedance

  base_quantity = "impedance"
  Examples of Specific Quantities:
  "acoustic_impedance"
  "characteristic_acoustic_impedance"
  "characteristic_electrical_impedance"
  "electrical_impedance"
  "mechanical_impedance"
  "nominal_electrical_impedance"
  "specific_acoustic_impedance"
  "wave_impedance"

  Examples

None yet

• Electrical impedance is a complex-valued quantity, where the real part is the familiar resistance (with SI unit "ohm") and the imaginary part is the less-familiar reactance.

• Admittance is defined as the inverse of impedance, and is therefore also complex-valued. Its real part is called conductance (with SI unit "siemens") and its complex part is called: susceptance.

• See: Acoustic impedance, Electrical impedance, Impedance (Accelerator Physics), Mechanical impedance and Wave impedance.

• Also see: Capacitance, Electrical reactance, Electrical resistance and Inductance.

Impulse

  base_quantity = "impulse"
  Examples of Specific Quantities:
  "impact_impulse"

  Examples

baseball-bat_baseball__impact_impulse

• An "impulse" quantifies the change in linear momentum that results from a force applied over a time interval. It has units of (force x time), and SI units of [N s].

• See: Impulse (physics).

Increment

  operation_prefix = "increment_of"

  Examples

atmosphere_air__increment_of_pressure
bedrock_surface__increment_of_elevation
land_surface__increment_of_elevation

• This can be used for the change in a quantity that occurs over some time period, such as a model time step. Models often update state variables with each time step by an incremental amount and this amount may be the quantity of interest. Note that an increment can be positive or negative.

• Before 3/19/13 this was treated as a quantity suffix but now it is treated as an "operation prefix". See Anomaly, Component, Limit, Magnitude, Ratio and Scale.

• For an "increment_of_time", the quantity suffix "step" is usually used instead of "increment". See the Step and Time Step templates.

Index

  base_quantity = "index"

  Examples

atmosphere_air_radiation__standard_refraction_index
consumer__price_index
ecosystem__diversity_index
land_surface__topographic_wetness_index
model_grid_cell__column_index
model_grid_cell__row_index
__normalized_difference_vegetation_index   ################
__palmer_drought_index

• The word "index" serves as a base quantity in the CSDMS Standard Names. It has two distinct meanings. One meaning of index is a subscript to an array, as used in "model_grid_cell__column_index" and "model_grid_cell__row_index" above. In this case, the index is a nonnegative integer. A second, and widely-used meaning for index is a composite statistic or measure. See the Wikipedia article: Index (statistics). Examples of this type include: Consumer Price Index, Normalized Difference Vegetation Index, Palmer Drought Index, Topographic Wetness Index and Urban Accessibility Index and others listed below.

• In order to distinguish between many different indices of a certain type, such as an urban accessibility index, the last names of the author who introduced a particular index and possibly also the publication year can be used as a prefix to disambiguate.

• We use "refraction_index" instead of "refractive_index" in accordance with the Process_name + Quantity Pattern. See Attributes of Radiation for information on the "standard_refraction_index".

• See Coefficient, Constant, Exponent, Factor, Number and Parameter.

• See: Diversity index, Forest fire weather index, Haines index, Heat index, Index (economics), Index (statistics), Jaccard index, Lifted index, Normalized Difference Vegetation Index, Palmer drought index, Price index, Producer Price Index, Refraction index and S & P Dow Jones Indices, Stock market index, Topographic Wetness Index.

Inertia

  base_quantity = "inertia"
  Examples of Specific Quantities:
  "rotational_inertia"
  "thermal_inertia"

  Examples

projectile__rotational_inertia
sea_water__thermal_inertia

• The term inertia by itself refers to a property of an object that depends on its mass, and isn't a quantity. However, this concept lends its name to the quantity names "rotational inertia" (also called moment of inertia) and "thermal inertia".

• The concept of inertia comes from Newton's first law of motion and can be stated as: "When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted on by an external force." It is often summarized with the adage: "Objects in motion tend to stay in motion. Objects at rest tend to stay at rest."

• Rotational inertia is also called "moment of inertia" and is a measure of the resistance to an object to changes in its angular momentum.

• The thermal inertia of a material is a measure of its resistance to changes in temperature. It is defined as the square root of the product of thermal conductivity, mass density and mass specific thermal capacity.

• Thermal inertia is an "intensive property" since it involves mass specific thermal capacity.

• See Inertia, Moment of inertia (rotational inertia), Thermal effusivity and Thermal inertia.

Intensity

  base_quantity = "intensity"
  Examples of Specific Quantities:
  "luminous_intensity" (optics)
  "radiant_intensity" (optics)
  "sound_intensity" (or "acoustic_intensity")

  Examples

atmosphere_air_radiation~incoming~shortwave__energy_intensity   [ W m-2]  ############# energy_flux ??

• Intensity is an overloaded term, but often means "power per unit area" and is therefore equivalent to an "energy flux".

• It is not yet clear when (or if) the CSDMS Standard Names should use "intensity" instead of "energy_flux", which is more descriptive. See Flux.

• See: Intensity (physics), Radiant intensity and Sound intensity.

Latitude

  base_quantity = "latitude"
  Examples of Specific Quantities:
  "authalic_latitude"
  "conformal_latitude"
  "geocentric_latitude"
  "geodetic_latitude"
  "isometric_latitude"
  "rectifying_latitude"
  "reduced_latitude"

  Examples

model_grid_cell_center__geodetic_latitude
model_grid_cell_edge~north__geodetic_latitude
model_grid_cell_edge~south__geodetic_latitude
model_grid_edge~north__geodetic_latitude
model_grid_edge~south__geodetic_latitude

• For an ellipsoid (of the type used to model the shapes of planets), there are many different ways to define latitude, but really just one way to define longitude. This is because the longitude lines (meridians) trace out ellipses (of the same size and shape) while the latitude lines are circles (of different sizes). When unqualified, the word "latitude" usually refers to geodetic latitude. The other six types of latitude are called "auxiliary latitudes" and are used for special problems in geodesy. Full explanations of these different types of latitude are provided at the links below.

• For a spheroid, the various definitions of latitude become the same. This is because the equatorial and polar radius are then the same, so the flattening, f, and eccentricity, e, are both zero. This can be checked by inserting e=0 into formulas for auxiliary latitudes.

• Typical units for latitude are "decimal degrees".

• This quantity is always relative to a particular (reference) ellipsoid model which should be specified using an <ellipsoid> tag in the Model Coupling Metadata (MCM) file. Similarly, <datum> and <projection> tags can be used. An <assume> tag should also be used to specify "geographic_coordinate_system".

• Note: Should we use "geographic_grid" instead of just "grid" for the object name in the examples above?

• See the sections for Coordinates and Longitude.

• See: Colatitude, Geodetic datum, Geographic coordinate system, Geographical distance, Latitude, Longitude, Meridian arc and Reference ellipsoid.

Limit

  operation_prefix = "limit_of"

  Examples

human__lower_limit_of_hearing_frequency     (Note:  hearing is a process name)
human__upper_limit_of_hearing_frequency
human_eye_photon__lower_limit_of_detection_number   (process_name + quantity)
star~neutron__tolman_oppenheimer_volkoff_limit_mass
star~white-dwarf__chandrasekhar_limit_mass

• Before 3/19/13 this was treated as a quantity suffix, but now it is treated as an "operation prefix". See Anomaly, Component, Increment and Magnitude. A "limit" is not a quantity by itself, but is an operation that can be applied to virtually any quantity.

• For clarity, it is often necessary to insert an adjective like "lower" or "upper" before the word "limit", as in the examples above.

• Note that the two limits above named after people include the quantity name "limit_mass" instead of "limit_of_mass". There is also a related "Schwarzchild radius"; see the quantity template for Radius. It is not clear that "_limit" would ever be used by itself. See Point.

• "cutoff" or "threshold" may sometimes be used similarly.

Longitude

  base_quantity = "longitude"

  Examples

model_grid_cell_center__longitude
model_grid_cell_edge~east__longitude
model_grid_cell_edge~west__longitude
model_grid_edge~east__longitude
model_grid_edge~west__longitude

• While there are several different ways to define latitude for an ellipsoid, there is really just one way to define longitude, as explained in the Latitude section.

• Since "center", "edge~east", "edge~west", etc. refer to parts of a cell, it is consistent with the use of similar words like "bottom" and "top" to include these in the object name part of the name (as of 7/23/14). Hyphens are used as shown here to clarify that "edge~east" is a single object or sub-object.

• Typical units are "decimal degrees".

• Typical units for longitude are "decimal degrees".

• This quantity is always relative to a particular (reference) ellipsoid model which should be specified using an <ellipsoid> tag in the Model Coupling Metadata (MCM) file. Similarly, <datum> and <projection> tags can be used. An <assume> tag should also be used to specify "geographic_coordinate_system".

• Note: Should we use "geographic_grid" instead of just "grid" for the object name in the examples above?

• See the sections for Coordinates and Latitude.

• See: Colatitude, Geodetic datum, Geographic coordinate system, Geographical distance, Latitude, Longitude, Meridian arc and Reference ellipsoid.

Magnitude

  "magnitude_of_" + [vector quantity]

  Examples

sea_bottom_water__magnitude_of_shear_stress
sea_water__magnitude_of_vorticity

• Magnitude is a general term in mathematics, used to indicate a scalar-valued "size" of something like a vector or complex number.

• The quantity name "speed" should be used instead of "magnitude_of_velocity".

• This was changed from a "quantity suffix" to a vector operation on 2/7/13. See CSDMS Operation Templates.

• In the CF Standard Names, "magnitude_of_" is a transformation (used as a prefix to an entire name) that is used in about 5 names.

Mask

  base_quantity = "mask"

  Examples

land_mask
ocean_mask

• In computer graphics and geographic information systems (GIS), the word "mask" is used to indicate a gridded (usually 2D or 3D) binary mask where two values (e.g. 0 and 1) are used to indicate whether or not a given feature or property is present in that grid cell. The term "data mask" is sometimes used to indicate that grid cells contain a data value if they are in the mask and a nodata value otherwise.

• A mask is often associated with a threshold value of some other grid of data. For example, a "land mask" may be set to 1 for every grid cell with an elevation value greater than 0 and set to 0 otherwise. We could use a standard name like "elevation_threshold_mask" or "temperature_threshold_mask" and then define the threshold value and how the masked values are related to the threshold value (>, >=, <, <= or =) with an <assume> tag in a Model Coupling Metadata (MCM) file.

• Masks provide a mechanism to identify a subset of a larger set, so they are a way to refer to a part of a larger object. Because of this, it is reasonable to use "land-mask" as an object in the object part of a CSDMS Standard Name. However, it is also reasonable to use "binary_mask" as a quantity name since it indicates the possible values (0 and 1) and the absence of units. A "data mask", on the other hand, inherits the quantity name and units of the data. So it would be reasonable to use "data_mask_of" as an operation, as in "positive_data_mask_of_elevation".

• The CF Standard Names currently have two names that contain the word "mask", namely: "land_binary_mask" and "sunlit_binary_mask". The guidelines mention both "binary_mask" and "data_mask".

• Terms like "presence_mask", '"inclusion_mask" and "exclusion_mask" would fit the Process_name + Quantity Pattern.

• Note that painters use Masking tape to "mask off" areas that should not be painted.

• See: Binary image and Mask (computing).

Mass

  base_quantity = "mass"
  Examples of Specific Quantities:
  "molar_mass"
  "relativistic_mass"
  "rest_mass"

  Examples

### cesium_atomic_mass   (also relative_atomic_mass = atomic_weight)
electron__relativistic_mass
electron__rest_mass   (also invariant mass, intrinsic_mass, proper mass)
star~neutron__tolman_oppenheimer_volkoff_limit_mass
star~white-dwarf__chandrasekhar_limit_mass   (object = star~white-dwarf)

• The SI units for mass are kilograms.

• What about "biomass"?

• See Attributes of Atoms, Concentration, Flux.

• See: Added mass, Biomass, Invariant mass, Mass-energy equivalence, Mass in special relativity, Molar mass, Planck mass and Transverse mass.

Maximum

  Examples

basin_outlet_water_x-section__time_max_of_volume_flow_rate   (for "peak discharge')

• While we could use "max" as a quantity suffix, this is not unambiguous for quantities that can vary in both space and time, such as drainage basin discharge. It seems best to introduce "time_max_of_" and "domain_max_of_" as operations instead. See: CSDMS Operation Templates.

Miles per Gallon

• This is not allowed because it is not a good quantity name; it is really a units name. The associated concepts are "fuel_consumption" and "fuel_economy". The word "mileage" is sometimes used but is also a poor term.

• See the Fuel Efficiency template.

Minimum

  Examples

basin_outlet_water_x-section__time_min_of_volume_flow_rate

• While we could use "min" as a quantity suffix, this is not unambiguous for quantities that can vary in both space and time, such as drainage basin discharge. It seems best to introduce "time_min_of_" and "domain_min_of_" as operations instead. See: CSDMS Operation Templates.

Modulus

  base_quantity = "modulus"
  Examples of Specific Quantities:
  "bulk_modulus"
  "shear_modulus"
  "young_modulus"

  Examples

lithosphere__bulk_modulus
lithosphere__young_modulus

• This quantity is used in continuum mechanics and materials science to measure a material's resistance to different types of deformation, sometimes called rigidity or stiffness. It has units of pressure.

• Bulk, shear and Young's are different types of "elastic modulus".

• There are several different models for how the shear modulus of metals varies with pressure and/or temperature, such as the MTS, SCG and NP models. See: Shear modulus.

• See: Bulk modulus, Dynamic modulus, Elastic modulus, Lamé parameters, P-wave modulus, Poisson's ratio, Shear modulus and Young's modulus.

Number

  base_quantity = "number"
  Examples of Specific Quantities:
  "julian_day_number"
  "neutron_number"
  "proton_number"
  "quantum_number"
  "wavenumber"
  "winding_number"

  Examples

automobile__vehicle_identification_number   (i.e. VIN number)
carbon_isotope__neutron_number
iron_atom__neutron_number
iron_atom__proton_number
sea_surface_water_wave__wavenumber

• This quantity name is often used when the attribute being quantified can only take integer values, as in the examples above and detectors that count particles. The word "count" is used similarly.

• Many important dimensionless numbers also end with the word "number" and are often named after a person (e.g. Reynolds number). These are discussed in the Dimensionless Number template and they are typically not integers. Also the wave number need not be an integer.

• Sometimes, there are multiple definitions for a dimensionless number, so they aren't always interchangeable. For example, there are at least 4 types of Richardson number. One is the reciprocal of the square of the Froude number. Three others are used in atmospheric science and are preceded by the adjective "flux", "gradient" or "bulk" (an approximation to the gradient version). For some definitions, the Richardson number can only take positive values, while for others it can also take negative values, which indicates an unstable atmosphere. The AMS provides several definitions of the Richardson number.

• Atomic number is a synonym for "proton_number" but the latter is used for clarity and consistency in the CSDMS standard names. The "mass_number" is defined as the sum of the "proton_number" and "neutron_number".

• Atomic physics uses several quantum_numbers, including the: principal quantum number, azimuthal quantum number, magnetic quantum number, spin quantum number and topological quantum number.

• Several other "numbers" are defined in particle physics, such as the "electronic_number", "muonic_number" and "tauonic_number".

• The winding number is used in mathematics as an attribute of closed, planar curves.

• See: Atomic number, Lepton number and Neutron number.

• Unique identification numbers are often assigned to people and other objects. See Credit card number,Employer Identification Number (EIN), Enzyme Commission Number, National Identification Number, Numbering scheme, Social Security Number, Transporter Classification Number and Vehicle Identification Number (VIN).

• In the branch of mathematics called number theory there are many special numbers, often named after a famous person. The Online Encyclopedia of Integer Sequences (OEIS) maintains an extensive database of information on integer sequences. See: Bell number, Catalan number, Euler number, Fibonacci number, Hardy-Ramanujan number, Kaprekar number, Lucas number, Prime number and Smith number. Also see the template for Constants in Math.

• For hydrologic features such as rivers, unique identification numbers such as the USGS Hydrologic Unit Code (or "HUC number") and Pfafstetter Code are used. See Code.

• See the Count template and Julian day.

Parameter

  base_quantity = "parameter"

  Examples

channel_bottom_water_flow_sediment__shields_parameter
channel_water_flow__manning_n_parameter
soil_water__van_genuchten_alpha_parameter

• Parameters often occur in empirical laws.

• The CSDMS Standard Names use "manning_n_parameter vs. "manning_coefficient".

• The CSDMS standard names use "coriolis_frequency" vs. "coriolis_parameter".

• Shields (1935) worked with a nondimensional shear stress that is now known as the Shields parameter.

• See templates for Coefficient, Constant, Exponent, Factor, Index and Number.

Partial Pressure

  base_quantity = "partial_pressure"
  Examples of Specific Quantities:
  name = [substance 1] + "_" + [substance 2] + "_partial_pressure"

  Examples

atmosphere_carbon-dioxide__partial_pressure   # (carbon dioxide in air)
atmosphere_water~vapor__partial_pressure  # (water vapor in air)
atmosphere_water~vapor__saturated_partial_pressure

• This is an example of a quantity that uses the Object-in-object Quantity Pattern because two substances are involved. See Solubility and Volume Fraction.

• The term "water vapor pressure" refers to the partial pressure of water vapor in air, and the "saturated water vapor pressure" is the partial pressure of water vapor in air at saturation. The CSDMS standard names for these are given above. One of them uses the Saturated Quantity Rule.

• Partial pressure for a gas dissolved in a liquid is the partial pressure of that gas which would be generated in a gas phase in equilibrium with the liquid at the same temperature. See: Partial pressure.

• CF Standard Names currently has only 6 names with "partial_pressure". They all have units of [Pa] and are:

surface_carbon_dioxide_partial_pressure_difference_between_air_and_sea_water
surface_carbon_dioxide_partial_pressure_difference_between_sea_water_and_air
surface_molecular_oxygen_partial_pressure_difference_between_sea_water_and_air
surface_partial_pressure_of_carbon_dioxide_in_air
surface_partial_pressure_of_carbon_dioxide_in_sea_water
water_vapor_partial_pressure_in_air   (alias: water_vapor_pressure)

We could use the following CSDMS standard name for the first quantity listed above:

"sea_surface_air-vs-water_carbon-dioxide" + "difference_of_partial_pressure"
(with "difference" as a quantity suffix).  Or with a new rule for "-and-in_", we could use:
surface_carbon_dioxide_in_air-and-in_sea_water_partial_pressure_difference.

• See the quantity template for Pressure.

Perimeter

  base_quantity = "perimeter"

  Examples

basin_boundary__perimeter
channel_x-section__perimeter

• This quantity has units of length and is well-defined for virtually any (nonfractal) planar shape. It can be infinite, however, for a fractal shape such as the Koch snowflake.

• See Diameter.

Period

  base_quantity = "period"
  Examples of Specific Quantities:
  "sidereal_period"
  "synodic_period"

  Examples

earth__rotation_period
flood__expected_return_period    ######### Need a flood size adjective.
mars_orbit__sidereal_period
mars_orbit__synodic_period
sea_surface_water_wave__period
virus_chicken-pox__incubation_period

• This quantity has units of time and is typically used to describe the time required for some time of periodic motion to return to its starting point. Examples include the rotation of a planet on its axis, the orbit of a planet around the sun or the period of a wave.

• In hydrology the terms: Return period, "return time", "recurrence interval" and "flood frequency" are used to quantify the expected time between floods of a given size.

• See: Orbital period for definitions of "sidereal period", "synodic period", "draconic period", "anomalistic period" and "tropical period".

• The Process_name + Quantity Pattern is often used, as in: "digestion period", "dormant period", gestation period, Hibernation period, incubation period, rotation period, "sleeping period"], waiting period and wave period.

• See Duration and Time.

Permeability

  base_quantity = "permeability"

  Examples

sea_bottom_sediment__permeability

• Permeability is a property of a geologic material (and not the fluid) that indicates the ability of a fluid to move through it. It is related to hydraulic conductivity.

• See Hydraulic conductivity and Permeability (earth sciences).

pH

  base_quantity = "ph"

  Examples

channel_water__ph
sulfuric-acid_solution__ph

• This quantity measures the activity of the (solvated) hydrogen ion in a solution. It is close to 7 for pure water, less than 7 for acidic solutions and greater than 7 for basic (i.e. alkaline) solutions.

• Should "pH" be viewed as a measurement unit instead of a quantity?

• See: Wikipedia: pH.

Point

  Examples

boiling_point
breaking_point  ??
bubble_point
critical_point   (See: Critical point.)
curie_point  (See: Curie point.)
dew_point
flash_point
freezing_point
frost_point
melting_point
wilting_point    (used in infiltration theory)
yield_point   (See: Yield strength.)

atmosphere_water~vapor__dew_point_temperature
atmosphere_water~vapor__frost_point_temperature
ice__melting_point_temperature
water__boiling_point_temperature
water__freezing_point_temperature

• This is not viewed as a quantity or quantity suffix within the CSDMS Standard Names. It is generally inserted just before a base quantity name and refers to a threshold that occurs for that quantity. See the template for Temperature for many examples.

• Each of the examples above puts a "process name" prefix, from the list of process names in CSDMS Process Names in front of "_point".

Porosity

  base_quantity = "porosity"

  Examples

soil__porosity

• Could also be called "soil_air__volume_fraction".

Power

  base_quantity = "power"

  Examples

channel_water__power

• "Power" has SI units of [J s-1] = [ W ]. In the context of a fluid in motion, it is an "energy flow rate" associated with the kinetic energy of the fluid. It is proportional to the cube of the fluid velocity. For a non-accelerating flow, the gravitational acceleration of the flow is exactly balanced by the loss of momentum due to friction. See the template for Flow Rate.

• In hydrology, the terms "stream_power" and "unit_width_stream_power" are used. See: Stream power.

Precipitation

  "precipitation_" + base_quantity
  "precipitation_leq-volume_flux
  "precipitation_mass_flux
  "precipitation_volume_flux

  Examples

atmosphere_water__precipitation_duration
atmosphere_water__precipitation_leq-volume_flux  (in liquid or solid form)
atmosphere_ice__precipitation_volume_flux
atmosphere_snow__precipitation_volume_flux
titan_atmosphere_methane__precipitation_leq-volume_flux (on Titan)

• Precipitation is not a quantity, but rather a process as defined at the top of the CSDMS Process Names page. However, there are several quantities associated with precipitation, as seen in the examples above. A "precipitation_volume_flux" has units of [length / time] (e.g. mm per hour) and a "precipitation_mass_flux" has units of [mass / time] (e.g. kg per hour).

• "Rainfall" is a somewhat unusual example of a process name in that the relevant object (rain) and the associated process (falling) have been fused to create the process name. Adding the object part in front would mean repeating the word rain. But "rain" is also a verb and "raining" is therefore a valid process name, but only for liquid water. The CSDMS Standard Names avoid this issue by using the process name "precipitation" instead of "rainfall" or "raining" and then specifying the object that is precipitating, such as "water" or perhaps "methane" for Titan.

• Since water can precipitate in liquid or solid form, each with a different density, precipitation rates are often quantified as liquid-water equivalent. The corresponding CSDMS standard name is: "atmosphere_water" + "precipitation_leq-volume_flux", where "leq-volume" is an abbreviation for "liquid-equivalent volume". This quantity name generalizes to other substances (like methane on Titan). See: Precipitation (chemistry) and Precipitation (meteorology).

• Note that in the CSDMS Standard Names, it is considered unnecessary and redundant to insert "liquid_equivalent" into the names "ice" + "melt_volume_flux" and "snowpack" + "melt_volume_flux", since the process of melting converts ice and snow to liquid water.

• The name "snowpack" + "liquid_equivalent_depth" is also used and is computed by multiplying the snowpack depth by the "liquid-water-to-snow_density_ratio".

• The word "water" by itself does not indicate whether the state is gas, liquid or solid.

• See the templates for Process Attributes and Rates of Processes for more information.

Pressure

  base_quantity = "pressure"
  Examples of Specific Quantities:
  "dynamic_pressure"
  "osmotic_pressure"
  "radiation_pressure"
  "partial_pressure" (See Partial Pressure above)
  "stagnation_pressure"
  "static_pressure"
  "total_pressure"
  "vapor_pressure"

  Examples

atmosphere_bottom_air__pressure
channel_bottom_water__static_pressure
channel_bottom_water_flow__dynamic_pressure
channel_bottom_water_flow__total_pressure  
channel_water__static_pressure
channel_water_flow__dynamic_pressure       (anywhere in the channel)
channel_water_flow__total_pressure

• Pressure may be thought of as "force per unit area".

• There is a distinction between static pressure and dynamic pressure. The first results from the weight of fluid above a location (called "hydrostatic" when the fluid is water) while the second is the kinetic energy per unit volume of a fluid flow. The "total pressure" is the sum of these two contributions. Also see: Bernoulli's principle, Pressure and Stagnation pressure.

• Pressure requires specifying a single object (e.g. air) but "partial pressure" requires two different objects to be specified using the "object-in-object" pattern. See the quantity template for Partial Pressure.

• In chemistry, the term vapor pressure (also called "equilibrium vapor pressure") has a specific meaning, and is a property of a single compound or substance.

• In meteorology, the term "vapor pressure" is used to mean the partial pressure of water vapor in the atmosphere, even if it is not in equilibrium, and the adjective equilibrium is inserted otherwise. In the CSDMS Standard Names, the term "vapor pressure" is only used as it is defined in chemistry, and for meteorology, names use "partial_pressure" or "saturated_partial_pressure" as in: "atmosphere_air_water~vapor" + "partial_pressure".

• Electromagnetic radiation exerts radiation pressure on an illuminated surface. A Crookes radiometer is often used to illustrate this effect, but it is now known that a combination of Einstein and Reynolds forces (thermal transpiration) is actually responsible for making them turn.

• The quantity pressure head is used in hydraulics and in ground water modeling but it has units of length. It is often negative, and negative pressure is sometimes called suction. See Head.

• In geology, the term overburden pressure or confining_pressure, is used.

• Although the pressure generated by a sound wave is sometimes called sound pressure, the standard name would then be something like: "air_sound-wave" + "pressure".

• In cosmology, there is also a concept of "negative pressure".

• Note that "atmosphere_bottom_air" + "pressure" and "land_surface_air" + "pressure" would mean the same thing, but the former is preferred.

• See: Atmospheric pressure, Dynamic pressure, Osmotic pressure, Overburden pressure, Partial pressure, Pressure, Pressure head, Radiation pressure, Stagnation pressure, Static pressure, Surface tension and Vapor Pressure.

Process Attributes

  [ process name ] + [ base_quantity ]

  Examples

digestion_period, gestation_period, hibernation_period,
incubation_period, sleeping_period
-------------------------------------------------------------------
lapse_rate, 
-------------------------------------------------------------------
evaporation_mass_flux, infiltration_mass_flux, melt_mass_flux,
precipitation_mass_flux
 
evaporation_volume_flux, infiltration_volume_flux, melt_volume_flux,
precipitation_volume_flux
-------------------------------------------------------------------
conception_date
delivery_date        (vs. "expected_delivery_date" or "due_date")
launch_date
ovulation_date
starting_date        (or "start_date" ??)
----------------------
precipitation_duration
sunshine_duration
----------------------
failure_frequency
oscillation_frequency
vibration_frequency
wave_frequency        (vs. "waving")
----------------------
recovery_time
starting_time
stopping_time
----------------------
flow_speed
running_speed
wind_speed    (Note: "wind" = "air_flow".)
----------------------
birth_weight
dissociation_energy
penetration_depth
striking_distance
turning_radius

• Many quantity names are created by pairing a process name with a base quantity name. See the Process Name + Base Quantity Name Pattern are given on the CSDMS Process Name + Quantity Name Pattern page for a long list of examples.

• Process names are almost always generated by converting a verb to a noun with a standard ending like "tion". See CSDMS Process Names for details and a long list of examples.

• Pairing a process name with the base quantity name "rate" makes sense for most processes, but a given process if often naturally associated with other base quantities (e.g. gestation_period). See the Rate template for examples where the base quantity is "rate".

• In the example of "birth_weight", "birth" is a process that is happening to the baby, while "delivery" or "giving birth" is the process happening to the mother. (i.e. "infant_birth_weight" and perhaps "pregnant_female_delivery_date")

Radiation

  "radiation_" + quantity

  Examples

light-bulb~incandescent__radiant_intensity   ? ##### CHECK
universe__cosmic_background_radiation_frequency

• See the CSDMS Standard Names Examples page for many examples where "radiation" is viewed as an object and appears in the object part of the name and the quantity is an energy_flux. These examples include the atmosphere, glacier, land_surface, sea_water and snowpack. Together they cover most of the Earth's basic radiation budget.

• Note that "radiation" (the process where an object generates and sends out energy) and "irradiation" (the process where an object receives energy from a source) are really distinct processes, and neither is a quantity by itself. The object in the object part of the name is either radiating energy or being irradiated by some external source of energy. However, as of 7/23/14, the adjectives "incoming" and "outgoing" are used instead of distinguishing between these two process names. (Similarly, "inflow" and "outflow" will not be used for fluid flow quantities.) This provides additional flexibility with semantic matching and provides a single, general and more easily understood rule. Quantity names can be constructed using the Process_name + Quantity Pattern. See the Process Attributes template.

• Incoming fluxes generated externally (from the point of view of the object name) and outgoing fluxes generated internally both have positive signs, by convention.

• The adjectives "upwelling" and "downwelling" are frequently used to mean "from the ground" and "from the sky". Note that "upwelling" longwave radiation would include longwave radiation emitted by the land surface as well as longwave radiation reflected from the land surface, but originally emitted from clouds or aerosols. So far, these adjectives are not used in the CSDMS Standard Names.

• Adjectives like longwave, shortwave, microwave, visible, infrared, thermal-infrared, ultraviolet and so on are typically inserted just before the word radiation.

• In a vacuum (e.g. space), the refraction index for all wavelengths of light is 1, so the speed of light is independent of wavelength. In other media, such as air and water, the refraction index (and therefore the speed) varies with wavelength. See the Index template.

• Radiation fluxes are energy fluxes (see the Flux template) and have SI units of [W m-2] = [J m-2 s-1].

Radius

  base_quantity = "radius"

  Examples

automobile__turning_radius
black-hole__schwarzchild_radius
earth_ellipsoid__equatorial_radius
earth_ellipsoid__polar_radius
railway_curve__minimum_radius    (see link below)

• See the Wikipedia pages for: Bend radius, Bohr radius, Classical electron radius, Covalent radius, Earth radius (which gives several possible definitions), Filling radius, Ionic radius, Minimum Railway Curve Radius, Radius of curvature (mathematics), Schwarzschild Radius, Turning Radius, Van der Waals radius and Wigner-Seitz radius.

• What about Radius of Curvature? See the object template for Surface.

Rate

  base_quantity ="rate"
  Examples of Specific Quantities:
  [ process name ] + "_rate"

  Examples

atmosphere_air__temperature_lapse_rate
automobile_fuel__consumption_rate
glacier_terminus__calving_rate
human_alcohol__consumption_rate

• The word "rate" means per unit time and is often paired with a process name to create a quantity name that quantifies how fast the process occurs, as in the examples above.

• Quantity names like: "evaporation rate", "infiltration rate", "melt rate" and "precipitation rate" are ambiguous because these rates can be quantified with either a mass flux [kg m-2 s-1] or a volume flux [m s-1]. (The latter is what is usually meant.) So, for example, we can have "glacier_ice" + "melt_mass_flux", "glacier_ice" + "melt_volume_flux", "evaporation_mass_flux", "evaporation_volume_flux", etc.

• Many examples of process names (and a definition) are given on the CSDMS Process Names page.

• Many examples of the Process Name + Base Quantity Name Pattern are given on the CSDMS Process Name + Quantity Name Pattern page.

• When necessary for clarification, the standard assumption name "liquid_equivalent" can be included with an <assume> tag in a Model Coupling Metadata (MCM) file. It seems that the quantity "ice_melt_rate", however, implies a rate at which water is being generated. In the CSDMS Standard Names, "leq-volume" is used as an abbreviation for "liquid-equivalent volume". In the CF Standard Names, "lwe" is used as a standard abbreviation for "liquid_water_equivalent" and this abbreviation is used as an adjective.

• Terms like "rainfall_rate" and "rain_rate", though commonly used, do not lend themselves to our general (object + quantity) pattern. Note that "rainfall" is a contraction of object (rain) and process (falling) names.

• See Precipitation.

Ratio

  base_quantity = "ratio"
  Examples of Specific Quantities:
  "aspect_ratio"
  "bowen_ratio"
  "dilution_ratio"
  "mass_ratio"

  Examples

bear_brain-to-body__mass_ratio
earth_ellipsoid__inverse_of_flattening_ratio
engine_air-to-fuel__mass_ratio     (or "mixture_ratio")
fuel-to-oxidizer__equivalence_ratio   ###
image__aspect_ratio
lake__bowen_ratio
lithosphere__poisson_ratio
rocket_payload__mass_ratio
rocket_propellant__mass_ratio
 
channel_x-section__width-to-depth_ratio  
electron__charge-to-mass_ratio

• Some ratios are the ratio of the same quantity as measured for two different objects while others are ratios of two different quantities measured on a single object. The Object-to-object Quantity Pattern is used for the first case and the Quantity-to-Quantity Pattern is used for the second case. Examples for both cases are given above.

• Ratios are often dimensionless. In fact, most dimensionless numbers are ratios of forces, etc. See the Dimensionless Number template.

• "ratio" serves as a quantity suffix in quantities like "mass_ratio", but is also allowed as a base quantity.

• Note that "relative_roughness" is a quantity that is defined as the ratio of the roughness length scale and the water depth in a channel. So channel_bed_relative_roughness is a valid standard name but channel_bed_roughness_length-to-water_depth_ratio is also valid.

• "aspect_ratio" generally means the ratio of the lengths of the long and short sides of a rectangle; 1 for a square and > 1 otherwise.

• In chemistry, "dilution_ratio" and "dilution_factor" are used for a solute in a solvent.

• In meteorology and hydrology, the Bowen ratio is defined to be the ratio of sensible and latent heating of a water body.

• In geodesy, the "flattening ratio" and "inverse flattening ratio" are used to characterize a standard ellipsoid. See Flattening.

• There are many ratios in economics, including "debt-to-credit_ratio", Debt ratio, Debt-to-GDP ratio, Debt-to-income ratio and Loan-to-value_ratio.

• See Fineness ratio, Mass ratio, Poisson ratio, Power-to-weight ratio and Ratio.

Reference Quantities

  "reference_" + quantity1 + "_" + quantity2
  quantity1 + "_reference_" + quantity2

  Examples

atmosphere_air_radiation__standard_refraction_index
  
land_surface_wind__reference_height_speed
land_surface_wind__speed_reference_height    ("reference" is between the quantities)
  
sea_surface_air__reference_pressure  ??   (insert "dry" before "reference"?)
sea_surface_air__reference_temperature ??
 
soil__reference_depth_temperature
soil__temperature_reference_depth

• Many quantities are defined with respect to a reference value of some quantity such as: height, pressure, temperature or wavelength. For example, wind speed is often reported for a reference height of 10 meters. Similarly, a model may require soil temperature at a reference depth of 1 meter.

• The "standard refraction index" for a given medium (e.g. air, water, vacuum) is given for a reference wavelength of 589 nm. For the latter, an <assume> tag should be included in the Model Metadata File that specifies: "at_reference_wavelength_of_589_nm" (and maybe also "yellow_doublet_sodium_d_line_reference".)

• Note that this typically requires that two quantities be specified, e.g "reference_height" and "speed", that result in a matched pair of distinct quantity names. These two names follow the "quantity" patterns given above.

• These quantities typically contain a word like "reference" or "standard". These two words may be treated as reserved words in the CSDMS Standard Names.

• Many quantities are defined for "standard_temperature-and-pressure" or STP and this is one of the standardized CSDMS Assumption Names that can be specified with an <assume> tag. However, there is not one standard definition of STP. The IUPAC (International Union of Pure and Applied Chemistry) defines STP as air at a temperature of 0 degrees C and a pressure of 10^5 Pa. In the US and elsewhere, STP is defined as air at a temperature of 60 degrees F and 14.696 psia (1 atm). An additional <assume> tag will therefore be required to avoid ambiguity.

• Many quantities, such as geopotential height are defined relative to Earth's mean sea level or MSL. An <assume> tag is needed to define the corresponding reference value.

• Georeferenced quantities, such as elevation, require specifying a reference ellipsoid. There is typically an associated datum and a projection may also be specified. Standard names for ellipsoids, datums and projections are provided on the CSDMS Metadata Names page. They can be specified in a Model Metadata File using <ellipsoid>, <datum> and <projection> tags.

• In cumulative frequency analysis (e.g. flood frequencies), a reference value must be specified and this would also be done using an <assume> tag.

• One or more <assume> tags should be used in the Model Metadata File to define the reference quantity. For example, <assume> reference_height_is_10m </assume>. The value of the reference height ("10m" in this example) should not be given in the standard name itself.

• The quantity suffix "Anomaly" also requires providing <assume> tags in a Model Metadata File to specify how the "mean climatology" reference value is defined.

Reflectance

  base_quantity = "reflectance"
  Examples of Specific Quantities:
  "broadband_reflectance"
  "spectral_reflectance"

  Examples

atmosphere_air_radiation~incoming~longwave__reflectance

• Reflectance (also called "reflectivity") is the ratio of the power per unit area [W m-2] of electromagnetic radiation reflected by a surface to the original, incident power per unit area (or irradiance). It is a dimensionless number between 0 (for a perfectly black surface) and 1 (for a perfectly white surface).

• Absorptance + Reflectance + Transmittance = 1. See Reflectance and Transmittance below.

• Various authors recommend using the terms: Absorptivity, Emissivity, Reflectivity and Transmissivity as properties of a pure material and Absorptance, Emittance, Reflectance and Transmittance as the analogous terms for the characteristics of a specimen or sample. See: Palmer, J.M. (1994) Chapter 25: The measurement of transmission, absorption, emission and reflection, Handbook of Optics, 2nd ed., Part II, M. Bass, editor, McGraw-Hill, NY. (A PDF file is available here.)

• Reflectance is the square of the magnitude of the "reflection coefficient" from Fresnel's equation. In general, the refraction index and reflection coefficient are complex numbers, as they are for materials that can absorb radiation.

• The quantity "spectral reflectance" is the reflectance associated with a specific wavelength, while "broadband reflectance" is an integral over a range of wavelengths. If a radiation band like "shortwave" or "longwave" is specified in the object part of the name, then it is unnecessary to specify broadband or spectral in the quantity part.

• Albedo is a very closely related concept. See Albedo above.

• See: Absorbance, Albedo, Attenuation coefficient, Beer-Lambert law, Fresnel equations, Mass attenuation coefficient, Opacity (optics), Reflectance and Transmittance.

Resistance

  base_quantity = "resistance"
  Examples of Specific Quantities:
  "electrical_resistance"
  "stomatal_resistance"
  "specific_thermal_resistance"
  "thermal_resistance"

  Examples

None yet.

• Electrical impedance is a complex-valued quantity, where the real part is the familiar resistance (with SI unit "ohm") and the imaginary part is the less-familiar reactance. See Impedance above.

• Conductance is the inverse of resistance, with SI unit "siemens".

• There is also: Antibiotic resistance.

• See: Capacitance, Electrical reactance, Electrical resistance, Inductance and Thermal resistance.

Resistivity

  base_quantity = "resistivity"
  Examples of Specific Quantities:
  "electrical_resistivity" [siemens-1 m] or [ohm m]
  "hydraulic_resistivity" [m-1 s]
  "ionic_resistivity"
  "thermal_resistivity" [W-1 m K] (this is an intensive property; don't need to add "specific")

  Examples

snow__thermal_resistivity

• Resistivity is the reciprocal of conductivity and both are "intensive" properties, so the prefix "specific" is not needed.

• Resistance and conductance are also reciprocals, but are "extensive" properties.

• See: [http://en.wikipedia.org/wiki/Hydraulic_conductivity Hydraulic conductivity, Ionic conductivity, Thermal conductivity and Thermal resistance.

Scale

  quantity_suffix = "scale"
  Examples of Specific Quantities:
  "length_scale"
  "time_scale"
  "velocity_scale"

  Examples

*_batchelor_scale
*_kolmogorov_length_scale 
*_kolmogorov_time_scale
*_kolmogorov_velocity_scale
*_mesoscopic_length_scale
*_obukhov_length_scale
*_planck_length_scale
*_planck_time_scale
*_taylor_length_scale

• This is another quantity suffix, used to create new quantity names from existing quantity names. It often is used to indicate the value of a quantity that is as small as it can be for the given system and therefore able to serve as a natural unit of measure.

• The adjective "characteristic" is often inserted before the base quantity name, as in "characteristic_length_scale".

• See: Length scale, Kolmogorov microscales, Batchelor scale and Taylor microscale.

• See Natural units, Planck units, Planck length and Planck time.

• Other interesting length scales include the Obukhov length,Mesoscopic scale, Synoptic scale and Nanoscale.

Sinuosity

  base_quantity = "sinuosity"
  Examples of Specific Quantities:
  "downvalley_sinuosity"

  Examples

channel_centerline__downvalley_sinuosity
channel_centerline__sinuosity
channel_valley_centerline__sinuosity

• Sinuosity is a dimensionless measure of the extent to which a river channel wiggles or deviates from a more direct path. Although it can be defined in different ways, the result is always a number that is greater than or equal to 1.

• In geomorphology, the standard type of sinuosity — which we here call "downvalley_sinuosity" — is the ratio of the centerline length of a channel to the centerline length of the valley that contains that channel. However, the centerline length of a valley can be difficult to measure with Geographic Information System (GIS) software. The word "sinuosity" (without qualification) is the ratio of the centerline length of a channel to the straight-line distance between the two endpoints of the channel (i.e. "as the crow flies"). Note that "sinuosity" will always be greater than or equal to "downvalley sinuosity".

• Note that the word "centerline" is inserted in accordance with the Object_name + model_name Pattern (i.e. a model of the object in question for which "length" is well-defined) and seems preferable to "axis", "backbone" and "curve".

• Recall that a "geodesic" is the shortest path between two points in a space that may be curved. On the surface of a sphere, a geodesic is given by the "great circle" that passes through two given points on the sphere. In a plane, the geodesic is just the straight line segment or "chord" that connects the two points. Geometry in the plane is also called Euclidean geometry.

• Other types of sinuosity have also been defined in the literature, including: floodplain sinuosity, terrace sinuosity and meander belt sinuosity.

• Even in a channel with straight banks, one can define a "thalweg" sinuosity by using thalweg centerline length in the numerator.

• We could construct longer and more descriptive standard names for different types of sinuosities such as: <br\> "channel_centerline-to-valley_centerline" + "length_ratio" and <br\> "channel_centerline-to-straight_line" + "length_ratio".
  This may help to avoid ambiguity for the less common types of sinuosity. We could even replace "length_ratio" in these names with "sinuosity".

• The standard definitions of sinuosity and tortuosity appear to be identical. The term "sinuosity_index" is sometimes used, here called "downvalley_sinuosity". See: Sinuosity and Tortuosity.

• See: Chord, Geodesic and Meander.

Slope

  base_quantity = "slope"

  Examples

land_surface__slope

• Slope is a dimensionless measure of the local steepness of a surface. It is defined as the magnitude of the gradient of elevation. In 1D, it is computed as"rise over run".

• The term "slope_angle" is used for the angle, beta, such that: slope = tan( beta ), or beta = arctan( slope ).

• See: Aspect and Slope.

Solubility

  base_quantity = "solubility"

  Examples

water_carbon-dioxide__solubility
water_diethyl-ether__solubility
water_ethanol__solubility

• This quantity always involves two substances and therefore requires using the Object-in-object Quantity Pattern. However, use of the reserved word "in" is now deprecated. (7/23/14). Instead, the containing object is listed first, followed by those contained and multi-word object names are hyphenated. See the templates for Partial Pressure and Fraction (volume fraction) which are similar in this regard.

• The solubility of a gas in a solvent is directly proportional to the partial pressure of that gas in the solvent. See: Solubility.

• Miscibility is the property of liquids to mix in all proportions to form a homogeneous solution and is a closely related concept. It is not a quantity, however.

Span

  base_quantity = "span"

  Examples

airplane_wing__span
beam__span
bridge__span
human_life__span  ####  (or human_life__max_of_duration ??)

• Span is an unusual quantity name that may have units of length or time depending on the context.

• "Wingspan" is a contraction of an object name (part of another object) and a quantity name. An underscore is inserted in a CSDMS standard name to indicate that "span" is the base quantity.

• See: List of spans,Maximum life span, Span (in architecture), Span (as a unit) and Wingspan.

Speed

  base_quantity = "speed"
  Examples of Specific Quantities:
  "escape_speed"
  "relative_speed"
  "settling_speed"
  "terminal_speed"

  Examples

glacier_bottom__sliding_speed
land_surface_air_flow__speed

• The quantity name "speed" is equivalent to "magnitude_of_velocity". Velocity components use the "component_of" operation prefix. See the Component template.

• When applied to fluids, the word "flow" is added to the end of the object part of the name, as an abbreviation for "flow field". It was formerly inserted before the word "speed".

• "Velocity" is a vector quantity while "speed" is a scalar quantity. The CSDMS Standard Names may allow vector quantities so that models can attempt to retrieve all velocity components in one data structure.

• The quantity relative_speed is the speed of one object relative to another (which may also be moving, in an arbitrary direction). In general, the "relative speed" can be computed as the magnitude of the vector difference between the the velocity vectors of the two objects. Both objects must be named in the object part of the name as in: "aircraft_ground" + "relative_speed".

• See Velocity for "escape speed", "settling speed" and "terminal speed".

Step

  quantity_suffix = "step"

  Examples

model__time_step

• This is another quantity suffix (defined at the top) that is usually used when the base quantity is "time".

• While an increment can have either sign, a step is generally positive.

• See Increment and Time Step.

Strain

  base_quantity = "strain"

• Strain is a normalized measure of deformation in continuum mechanics and is therefore dimensionless.

• Different fluids and substances have different "stress-strain" relationships. For a Newtonian fluid, there is a linear relationship between the shear stress and the strain rate.

• See Deformation, Shear stress, Strain rate and Stress-strain curve.

Strength

  base_quantity = "strength"

  Examples

None yet.

• In physics, the "strength" of a vector field is simply its magnitude. See: Field strength and Signal strength. See Magnitude above.

• In materials science, the word "strength" often refers to a critical value of stress. See: Compressive strength, Shear strength, Tensile strength and Yield strength.

• See: Physical strength.

Stress

  base_quantity = "stress"
  Examples of Specific Quantities:
  "deviatoric_stress"
  "normal_stress"
  "shear_stress" (vs. "shearing_stress"; see below)

  Examples

channel_bottom_water_flow__magnitude_of_shear_stress
channel_bottom_water_flow_sediment_grain__shields_critical_shear_stress
sea_bottom_surface_water_flow__normal_component_of_stress
sea_bottom_surface_water_flow__x_z_component_of_shear_stress
sea_water_flow__down_east_component_of_stress
sea_water_flow__down_east_component_of_reynolds_stress
sea_water_flow__down_east_component_of_viscous_stress
sea_water_flow__down_north_component_of_stress

• Components of stress are specified using the "component_of" operation prefix, as shown in the examples above. For models that use a geographic coordinate system, we would use "east", "north" and "up" to describe component directions. For models that use a Cartesian (or equal-area) coordinate system, we would use "x", "y" and "z".

• Standard adjectives for shear stress include: "skin_friction", "form_drag" and "total".

• Conventions like "right_hand_rule" and "positive_downward" can be indicated in a Model Metadata File with <assume> tags.

• Perhaps we should introduce a convention where "shear_stress" is taken to mean "magnitude_of_shear_stress" when there is no operation prefix.

• Stresses are more complex than vectors and are represented mathematically as tensors.

• There are two "kinds" of stress called "normal" and "shear" stress. While a normal stress is associated with a single vector, two vectors are required to describe a shear stress.

• Note that "shearing_stress" follows the Process_name + Quantity Pattern, where the process name is "shearing". However, the "ing" ending is often dropped, as is often the case with process names; see the top of the CSDMS Process Names page. Many fluid dynamics textbooks use "shearing", e.g. Batchelor (1988), and "tangential stress" is a synonym.

• Reynolds stress is a contribution to the total stress tensor in a fluid due to momentum fluctuations that arise within turbulent flows. When "stress" appears by itself, it indicates the "total" stress tensor, which includes the so-called "viscous_stress" and the "Reynolds_stress" (or turbulent stress). (Is radiation stress also included in "total"? See below.)

• Shields (1935) introduced the concept of a "critical shear stress" that must be exceeded at the bed of a river channel in order to initiate sediment transport. The associated quantity name is "shields_critical_shear_stress", with the name "shields" being placed before "critical" to allow other definitions of "critical_shear_stress" by future researchers. We could use the Process Name + Base Quantity Name Pattern to construct a self-describing quantity name like: "transport_initiation_stress", "initial-transport_stress" or "initial-motion_stress".

• In oceanography there is a concept of radiation stress and for electromagnetic radiation there is radiation pressure. See Pressure.

• There are 19 CF Standard Names that contain the word "stress". Most contain only one "component adjective" like "eastward", but some have two, such as

surface_downward_eastward_stress
surface_downward_northward_stress
surface_downward_x_stress
surface_downward_y_stress

Temperature

  base_quantity = "temperature"
  Examples of Specific Quantities:
  "convective_temperature"
  "effective_temperature"
  "equivalent_temperature"
  "equivalent_potential_temperature"
  "potential_temperature"

  Examples

atmosphere_air_water~vapor__bubble_point_temperature
atmosphere_air_water~vapor__dew_point_temperature
atmosphere_air_water~vapor__frost_point_temperature
iron__melting_point_temperature
snow__temperature
soil__temperature
water__boiling_point_temperature
water__freezing_point_temperature

• Use "dew_point_temperature" vs. "temperature_at_dew_point". Similarly for "boiling_point", "melting_point", "freezing_point", etc.

• Can include how measured with <assume> tags in a Model Metadata File.

• Note that "apparent_temperature" or "heat_index_temperature" (same as "felt_air_temperature") may be less ambiguous standard names than "heat_index", since it has units of temperature.

• Materials with impurities or in very small quantities may melt at a lower temperature than bulk amounts of pure material. This is quantified with Melting-point depressions. In the CSDMS Standard Names, these use the operation prefix "depression_of" + "melting_point_temperature".

• See the Wikipedia pages for: Critical point, Curie point, Dew point, Hydrocarbon dew point, Bubble point and Flash point.

• See the Wikipedia pages for: Temperature, Equivalent temperature, Potential temperature, Equivalent potential temperature, Effective temperature, Color temperature, Brightness temperature, Atmospheric temperature, Sea surface temperature, Convective temperature, Dry-bulb temperature and Wet-bulb temperature.

Tension

  base_quantity = "tension"
  Examples of Specific Quantities:
  "surface_tension"

  Examples

• Tension is the opposite of compression. It is often used in connection with columns, ropes and strings.

• Tension is not a force, but has units of force (e.g. Newtons).

• See: Surface tension, Tension (physics) and Ultimate tensile strength.

Term

  base_quantity = "term"
  Examples of Specific Quantities:
  "acceleration_term"
  "convection_term"
  "diffusion_term"
  "forcing_term"
  "friction_loss_term"
  "sink_term"
  "source_term"
  "time_derivative_term" (or use "unsteady_term" instead?)

  Examples

equation~convection-diffusion__convection_term"
equation~convection-diffusion__diffusion_term"
equation~navier-stokes__body_force_term
equation~navier-stokes__convective_acceleration_term
equation~navier-stokes__pressure_gradient_term
equation~navier-stokes__unsteady_acceleration_term
equation~navier-stokes__viscosity_term    (or "viscous_diffusion_term" ?)
equation~poisson__laplacian_term
equation~poisson__source_term

• Many models allow various "terms" in an equation that the model solves numerically to be saved as output.

• In the Navier-Stokes equation, which is widely used for modeling fluid flow, each term has a standard name. The names are: "unsteady_acceleration_term", "convective_acceleration_term" (or "nonlinear_term"), "pressure_gradient_term" (or "pressure_term"), "viscosity_term" (or "diffusion_term" or "vector_laplacian_term") and "body_force_term".

• The convection-diffusion equation has a time derivative (or unsteady) term, a diffusion term, a convection term and source term.

• Many of the examples above follow the Process_name + Quantity Pattern. See the top of the CSDMS Quantity Templates page and the list of CSDMS Process Names.

• This template is still under review. The appropriate object_name (possibly an equation_name from the CSDMS Assumption Names page) and the associated units are not entirely clear. However, this type of quantity is commonly included among a model's output variables.

• We may also want to include "right_hand_side" and "left_hand_side", but this is dependent on how the equation is written.

• See: Field equation, Laplacian, Vector Laplacian, Poisson's equation, Pressure gradient and Shallow water equations.

Thickness

  base_quantity = "thickness"

  Examples

shale~burgess_stratum__thickness    ("stratum" or "layer" ?)
human_hair__thickness
mars_atmosphere__thickness
model_soil_layer~0__thickness
paper__thickness

• This quantity name refers to the full, top-to-bottom vertical length dimension of something that tends to cover an area that is large relative to this length.

• The words "depth" and "thickness" are sometimes used interchangeably. In the context of "layers", "thickness" is usually used (e.g. in meteorology, geology and hydrogeology). In the context of surface water or snow, "depth" is usually used. (As in: "How deep is the lake?" or "The lake depth is 5 meters.") The word "depth" indicates a value that is positive downward from some reference datum. There is often the connotation that it may take values less than some maximum possible value, as in "sea_water_secchi_disk_depth".

• See Altitude, Depth, Elevation and Height.

Threshold

  operation_prefix = "threshold"

  Examples

snow__threshold_of_degree-day-temperature  ### ??

• Before 3/19/13, this was treated as a "quantity suffix" but now it is treated as an "operation prefix". In the example above, however, the word "threshold" is used as an adjective. Perhaps it should contain more information, something like "melting_point_temperature".

• It is more common for words like "critical" or "point" to be inserted as an adjective in front of a base quantity name to indicate a threshold value. See the template for Temperature.

Time

  quantity_suffix = "time"

  Examples

channel_water__peak_time_of_volume_flow_rate
model__run_time
model__start_time
model__stop_time
model__time

• The quantity "time" can refer to the specific time associated with an event, such as "mars__local_rise_time", or to a duration, as in "relaxation_time".

• We may allow "time" to be used as a "quantity suffix" associated with an event like reaching a peak value. But this use case may also be handled using an operation prefix.

• This is commonly used in the Process_name + Quantity Pattern, as in "start_time" and "stop_time". Recall that the "ing" ending of many process names is dropped. See CSDMS Process Names.

• In the mathematics of stochastic processes, the quantities: Hitting time and Stopping time are used.

• In hydrology, the terms "return time", "return period", "recurrence interval" and "flood frequency" are used to quantify the expected time between floods of a given size. See Period.

• In astronomy, a "rise_time" and "set_time" can be defined for any celestial body and an observing location on Earth. See the US Navy's astronomical data services page. Note that these quantities require specifying two objects.

• See: Residence time, Relaxation time, Transition time, Arrival time (and ETA), Fall time, Lead time, Rise time and Holding time.

• See Duration and Period.

Time Step

  quantity_suffix = "step"
  base_quantity = "time"
  "time_step"

  Examples

model__time_step

• Note that "increment" and "step" are both quantity suffixes that do not change the units of the base quantity. "Step" is usually used when the base quantity is "time".

• See Increment and Step.

Transmittance

  base_quantity = "transmittance"
  Examples of Specific Quantities:
  "spectral_transmittance"

  Examples

atmosphere_air_radiation~incoming~longwave__transmittance

• Transmittance is the ratio of the power per unit area [W m-2] of electromagnetic radiation transmitted through something to the original, incident power per unit area (or irradiance). It is a dimensionless number between 0 and 1.

• Absorptance + Reflectance + Transmittance = 1. See Absorptance and Reflectance above.

• Various authors recommend using the terms: Absorptivity, Emissivity, Reflectivity and Transmissivity as properties of a pure material and Absorptance, Emittance, Reflectance and Transmittance as the analogous terms for the characteristics of a specimen or sample. See: Palmer, J.M. (1994) Chapter 25: The measurement of transmission, absorption, emission and reflection, Handbook of Optics, 2nd ed., Part II, M. Bass, editor, McGraw-Hill, NY. (A PDF file is available here.)

• While "transmissivity" can mean the transmittance of a pure material (see above), it is also used for a concept in ground water hydrology.

• The quantity "spectral transmittance" is the transmittance associated with a specific wavelength.

• See: Absorbance, Attenuation coefficient, Beer-Lambert law, Mass attenuation coefficient, Opacity (optics), Reflectance and Transmittance.

Unit-width (and similar) Quantities

  base_quantity

  Examples

human_blood_cell~red__count-per-volume
land_surface_water__volume-per-unit-contour-length_flow_rate
sea_surface_water_wave_crestline__power-per-unit-length

• CF Standard Names use "_across_unit_distance" and "_across_line" to handle this concept.

• "unit_stream_power" is somewhat similar.

• There are several other "per" concepts, such as:

per_capita
per_unit_area
per_unit_length
per_unit_mass
per_unit_time
per_unit_width
 

These could all be used as adjective or modifier prefixes for a base quantity.

Velocity

  base_quantity = "speed"
  Examples of Specific Quantities:
  "darcy_speed"
  "drift_speed"
  "escape_speed"
  "fall_speed"
  "flow_speed"
  "group_speed"
  "impact_speed"
  "initial_speed"
  "phase_speed" (also called "celerity")
  "settling_speed"
  "terminal_fall_speed"

  base_quantity = "velocity"
  Examples of Specific Quantities:
  "darcy_velocity"
  "drift_velocity"
  "group_velocity"
  "impact_velocity"
  "initial_velocity"
  "phase_velocity" (vector field of wave rays)
  "shear_velocity" (also called "friction velocity")

  "azimuth_angle_of_velocity"
  "elevation_angle_of_velocity"
  "x_component_of_velocity"
  "y_component_of_velocity"
  "z_component_of_velocity"

  Examples

atmosphere_ball__fall_speed
atmosphere_ball__terminal_fall_speed     ### (air_ball__** sounds strange)
earth__escape_speed    (vs. escape_velocity)
electron__drift_speed
water_sand_grain__settling_speed     # (sand grain in water)
 
electron__x_component_of_drift_velocity
electron__y_component_of_drift_velocity
 
sea_water_flow__east_component_of_velocity
sea_water_flow__north_component_of_velocity
sea_water_flow__up_component_of_velocity
sea_water_flow__speed
sea_water_flow__x_component_of_velocity
sea_water_flow__y_component_of_velocity
  
sea_water_wave~internal~gravity__group_speed
sea_water_wave~internal~gravity__phase_speed
sea_surface_water_wave__group_speed    ## wave~gravity ??
sea_surface_water_wave__phase_speed
 
soil_water_flow__x_component_of_darcy_velocity
soil_water_flow__y_component_of_darcy_velocity
 
sea_surface_air_flow__magnitude_of_shear_velocity
sea_surface_air_flow__x_component_of_shear_velocity
sea_surface_air_flow__y_component_of_shear_velocity

• Velocity is a vector quantity with a magnitude and a direction. Most models store the components of a velocity field as separate variables, in which case the operation component_of can be used as shown in the example above. (See the template for Component.) However, it is also possible that one model would request a complete vector field (i.e. all components) from another model as a single "quantity". Because of this, we need to allow "velocity" itself (a vector) as a base quantity name.

• In addition to the "component_of" operation, there are several other operations that can be used to identify an attribute of a vector, such as: "magnitude_of", "azimuth_angle_of" and "elevation_angle_of". For 2D vector fields, only the azimuth angle applies, but for 3D vector fields the elevation angle (from spherical coordinates) is also required. See the CSDMS Operation Templates.

• The quantity name darcy_velocity is used for 3D flow of water in soil to emphasize its macroscopic definition as a volume flux or "specific discharge". See the template for Attributes of Soil.

• The magnitude of the shear_velocity is defined as the square root of the shear stress (at a boundary) divided by the mass density. It is also called the "friction velocity". Shear velocity is a vector quantity, and its direction is the same as the shear stress component used to define it.

• The shorter quantity name "speed" is used in CSDMS standard names instead of "magnitude_of_velocity" but they mean the same thing. See Speed.

• The terms shear velocity, terminal velocity and escape velocity are all used but they each refer to a speed, or velocity magnitude. The "escape_speed" for Earth is a scalar quantity, independent of direction.

• Note that terminal velocity (called "terminal_fall_speed" here) is a quantity that requires two objects to be specified, an object and the fluid through which it is falling. The Object-in-object Pattern is therefore used. In the context of a particle falling through water, the term "settling velocity" (called settling_speed here) is commonly used.

• See: Angular velocity, Drift velocity, Flow velocity, Group velocity, Phase velocity, Proper velocity, Relative velocity, Soil mechanics (Darcy velocity) Stokes drift and Velocity.

• See the template for Speed.

Viscosity

  base_quantity = "viscosity"
  Examples of Specific Quantities:
  "apparent_viscosity"
  "dynamic_shear_viscosity"
  "dynamic_volume_viscosity"
  "eddy_viscosity"
  "extensional_viscosity"
  "kinematic_shear_viscosity"
  "kinematic_volume_viscosity"

  Examples

air__dynamic_shear_viscosity
air__dynamic_volume_viscosity
air__kinematic_shear_viscosity
air__kinematic_volume_viscosity
polymer__extensional_viscosity
sea_water__eddy_viscosity
water__dynamic_shear_viscosity
water__dynamic_volume_viscosity
water__kinematic_shear_viscosity
water__kinematic_volume_viscosity
water__x_z_component_of_viscosity

• Viscosity is a tensor quantity and is decomposed into "shear" and "volume" components that are analogous to the "shear" and "normal" components used for stress, another tensor quantity. "bulk viscosity" is a synonym for volume viscosity which is important for compressible fluids but is less well-known than shear viscosity.

• Since viscosity is really a tensor, we can refer to each of its possible components using the "component_of" operation; e.g. "x_z_component_of_viscosity".

• Viscosity depends on temperature, so a reference temperature should be provided with an <assume> tag in a Model Metadata File. For an ideal gas, Sutherland's formula gives dynamic viscosity as a power-law function of temperature. For a dilute gas, the Chapman-Enskog equation can be used. For liquids, several different models are available; see: Temperature dependence of liquid viscosity.

• Kinematic viscosity is just the dynamic viscosity divided by the density of the fluid. It is used in the definition of the Reynolds number.

• "The "eddy viscosity" concept is used to parameterize small-scale details in models of turbulent flow. It is sometimes contrasted with "molecular viscosity". Also see the Diffusivity template.

• The reciprocal of viscosity is called fluidity.

• See: Apparent viscosity, Viscosity, Inviscid flow, Large eddy simulation (LES), Newtonian fluid, Non-Newtonian fluid and Volume viscosity.

Voltage

  base_quantity = "voltage" [Volts = Joules per Coulomb]

  Examples

battery__voltage
appliance~electric__voltage
fence~electric__voltage

• See: Voltage and Voltage drop.

Vorticity

  base_quantity = "vorticity"
  Examples of Specific Quantities:
  "absolute_vorticity"
  "ertel_potential_vorticity" ### (a scalar quantity)
  "planetary_vorticity"
  "potential_vorticity"
  "relative_vorticity"

  Examples

sea_water_flow__down_component_of_vorticity
sea_water_flow__east_component_of_vorticity
sea_water_flow__magnitude_of_vorticity
sea_water_flow__north_component_of_vorticity
sea_water_flow__south_component_of_vorticity
sea_water_flow__up_component_of_vorticity
sea_water_flow__west_component_of_vorticity
sea_water_flow__x_component_of_vorticity
sea_water_flow__y_component_of_vorticity
sea_water_flow__z_component_of_vorticity

• Vorticity is a vector quantity defined as the curl of a fluid velocity (vector) field. The quantity name for a component of the vorticity vector uses the "component_of" operation prefix as shown in the examples above. See the Component template.

• Relative vorticity is the vorticity of air velocity relative to the Earth. When "vorticity" appears without an adjective, relative vorticity with respect to a fixed coordinate system is assumed. See: Relative vorticity.

• Absolute vorticity is "relative vorticity" plus "planetary vorticity". See: Absolute vorticity.

• Planetary vorticity is the vorticity associated with the rotation of the Earth.

• Potential vorticity is absolute vorticity divided by the vertical spacing between levels of constant entropy. It seems that there are two types of potential vorticity. Ertel's potential vorticity (ertel_potential_vorticity) is a scalar quantity, defined as a dot product of absolute vorticity and the gradient of potential temperature. See: Potential vorticity.

• Here, "flow" is used as a shorthand for "flow_field" in the object part of the name. This is an example of the Object Name + Model Name Pattern.

• Since the curl of any gradient vector is zero, taking the curl of the Navier-Stokes equation eliminates the pressure gradient term.

• See Vorticity, Circulation and Vector calculus identities.

Wavelength

  base_quantity = "wavelength"
  Examples of Specific Quantities:
  "compton_wavelength"
  "reduced_compton_wavelength"

  Examples

electron__compton_wavelength
sea_water_wave~internal~gravity__wavelength  (### or sea_internal_water_wave ??)
sea_surface_water_wave__wavelength
wave~airy__wavelength
wave~cnoidal__wavelength
wave~sine__wavelength
wave~stokes__wavelength

• The wavelength is the distance between successive crests or troughs in a periodic function.

• See the section called Attributes of Radiation above.

• See: Amplitude, Angular frequency, Compton wavelength, de Broglie wavelength, Frequency (and Period), Hertz, Thermal de Broglie wavelength, Wavelength, Wavenumber and Wave vector.

Wavenumber

  base_quantity = "wavenumber"

  Examples

sea_surface_water_wave__wavenumber
wave~airy__wavenumber
wave~cnoidal__wavenumber
wave~electromagnetic__wavenumber
wave~seismic__wavenumber
wave~stokes__wavenumber

• "Wavenumber" is a basic property of a periodic function or waveform, along with amplitude and wavelength.

• The wavenumber is the magnitude of the phase velocity vector field of a waveform. The streamlines of this vector field are the "rays", while the orthogonal set of curves are the wavefronts or crestlines.

• See Wavenumber and Wave vector.

Weight

  base_quantity = "weight"
  Examples of Specific Quantities:
  "volume-specific_weight"

  Examples

bear~alaskan~black__weight

• The weight of an object has units of force and is the product of its mass and the standard gravity constant for the planet on which the weight is being measured. (It actually even depends on distance above the planet's surface.) Because of this, perhaps we should use quantity names like "earth-weight" (or even "earth-surface-weight") and "mars-weight", etc.

• We could use "weight-per-volume" instead of "specific_weight".

• What about "submerged weight" ?

• See: Specific weight and Weight.

Yield

  base_quantity = "yield"
  Examples of Specific Quantities:
  "specific_yield" (in groundwater modeling)

  Examples

basin_outlet_sediment__yield

• In geology, "sediment yield" refers to the total mass of particulate matter (suspended or bedload) that reaches the outlet of a drainage basin over a fixed time interval. It has units of [mass / (area * time)] or [M L-2 T-1]. See: sediment yield.

• In agriculture, "crop yield" refers to the total amount produced (e.g. kilograms or bushels) per unit area. See: Crop yield and Yield (wine).

• What about "yield_strength" (plastic deformation) ? See: Yield (engineering).

• See also: Specific yield (groundwater), Yield (chemistry), Yield surface and Quantum yield.