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 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.
  
  

• 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 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", "scale", "step" or "threshold" (and in some cases "ratio") that produces a new quantity name from an existing quantity name (e.g. "elevation_increment"). The units are usually unchanged, but "fraction" and "ratio" are exceptions. In most cases, it would also be possible to use a quantity suffix as a an operation prefix. See the CSDMS Operation Templates. Also see the templates for Increment and the others listed above for more information.
  
  

• 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", "partial_pressure", "relative_saturation" (see Humidity), "solubility" and "volume_fraction". In such cases we use the reserved word "_in_" and the pattern: object = (object + "_in_" + object), 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__volume_fraction
silt_in_soil__volume_fraction
visible_light_in_air__speed      ### (possibly; See the Constants in Physics template.)
water_vapor_in_air__dew_point_temperature

Note that bubble_point_temperature, dew_point_temperature and frost_point_temperature also require one substance within another, as in: water_vapor_in_air_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 we insert the word "saturated" in front of the quantity name to define a new quantity. Examples include:

soil_saturated_hydraulic_conductivity
soil_saturated_water_content    (same as "water_in_soil_saturated_volume_fraction")
water_vapor_in_air_saturated_partial_pressure

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:

rubber_on_concrete_kinetic_friction_coefficient
rubber_on_pavement_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:

brain_to_body_mass_ratio
earth_to_mars_travel_time
earth_to_sun_mean_distance
 
carbon_to_hydrogen_bond_length
hydrogen_to_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".

• 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_cross_section_width_to_depth_ratio
electron_charge_to_mass_ratio    charge to mass ratio
electron_mass_to_charge_ratio
watershed_outlet_width_to_depth_ratio

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

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

aspect     = surface_gradient_angle   (direction relative to a fixed axis)
density    = mass_to_volume_ratio   (but density sometimes has other meanings)
discharge  = volumetric_flow_rate
slope      = surface_gradient_magnitude
speed      = velocity_magnitude   (or even "motion_rate"; process_name + quantity)

• Incoming and Outgoing Quantity Rule (Under review.) We may need a provision to indicate whether a vector quantity associated with a model grid cell is "incoming" or "outgoing". In the CF Standard Names, "incoming" is used in one name (namely, "toa_incoming_shortwave_flux") while "outgoing" is used in 6 names (always containing "toa_outgoing_longwave_flux" or "toa_outgoing_shortwave_flux"). Recall that "toa" = "top_of_atmosphere". But they are not used with respect to a model grid cell. Together with "grid_cell" as the object, we could have:

water_into_grid_cell_discharge
water_into_lake_discharge
water_from_grid_cell_discharge

where "into" and "from" would be new reserved words. Note that:

grid_cell_water_incoming_discharge and
grid_cell_water_outgoing_discharge
lake_water_incoming_discharge

comply with all of our naming rules. Recall that "discharge" is a short synonym for "volumetric_flow_rate". (Even though the word "discharge" connotes an "outflow".) With "inflow" and "outflow" as process names, we could also use:

grid_cell_water_volume_inflow_rate
grid_cell_water_volume_outflow_rate and
lake_water_volume_inflow_rate.

See the Discharge template.

Affinity

  base_quantity = "affinity"
  quantity = "chemical_affinity"
  quantity = "electron_affinity" (of an atom or molecule)

  Examples

chlorine_electron_affinity
magnesium_chloride_to_water_chemical_affinity
sulphuric_acid_to_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.

Altitude

  base_quantity = "altitude"

  Examples

airplane_altitude
skydiver_altitude

• The word "altitude" is reserved for objects that are above and not in contact with the land surface. (e.g. aircraft, air parcel, balloon) See the Elevation template. By contrast, "altitude" is used as a synonym for "elevation" in the CF Standard Names.

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

Angle

  base_quantity = "angle"

  Examples

azimuth_angle, bank_angle, bond_angle, declination_angle,
earth_axis_tilt_angle,  friction_angle, incidence_angle, inclination_angle,
pitch_angle, polarization_angle, repose_angle, roll_angle,
rotation_angle, scattering_angle, shock_angle, slope_angle,
torsion_angle, yaw_angle, zenith_angle

• There are two major conventions used for measuring angles. For bearings, the angle is 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 in the Model Metadata File with an <assume> tag using one of the standardized assumption names from 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.

• 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.

• A few terms sound strange in this form, like "repose_angle", instead of "angle_of_repose". But this doesn't pose any real problem.

• 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.

• 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".

• See: Aspect (geography), Orbital inclination and Slope.

Anomaly

  quantity_suffix = "anomaly"

  Examples

air_pressure_anomaly
air_temperature_anomaly
sea_surface_temperature_anomaly

• This is a quantity suffix that creates a new quantity from an existing base quantity like elevation or pressure. Others are 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"
  quantity = "drainage_area"
  quantity = "surface_area"

  Examples

channel_cross_section__area
channel_cross_section__wetted_area
glacier_surface__area
lake_surface__area
sphere_surface__area
watershed__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 watershed, such as "drainage area", "contributing area", "upstream contributing area", "total contributing area (TCA)" and "specific contributing area (SCA)". A watershed 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 the object is watershed, there is no need to distinguish between "watershed_area" and "watershed_drainage_area", so "drainage" is dropped.

• 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.

Attributes of Atoms

  quantity = attribute
  quantity = "atomic_mass"
  quantity = "emission_frequency"
  quantity = "relative_atomic_mass" (dimensionless ratio to carbon-12)
  quantity = "mass_number" (number of protons + neutrons)
  quantity = "neutron_number" (number of neutrons)
  quantity = "proton_number" (number of protons)

  Examples

carbon_isotope_neutron_number  (use "isotope" like this ??)
cesium_atom_proton_number
cesium_atom_relative_atomic_mass

• There is controversy over the term "atomic_weight" and the term "relative_atomic_mass" seems preferably and more precise.

• While "atomic number" is a standard term, the synonym "proton_number" is winning favor because it is more specific and because "neutron_number" is also used.

• A specific frequency in the emission spectrum of cesium-133 is used for the ISU definition of the "second", so cesium is used in atomic clocks. It is not really a characteristic vibration frequency of the atom. (But molecules do have vibration frequencies; see Attributes of Molecules below.) It is a transition or resonance frequency between two hyperfine ground states of cesium-133. A CSDMS standard name for this frequency could be something like: "cesium_133_isotope_state1_to_state2_hyperfine_transition_frequency", where "state1" and "state2" would be replaced with appropriate names for the two states involved.

• See the CSDMS Object Template for Atoms, Compounds, Ions and Molecules below for more information.

Attributes of Channels

  quantity = attribute
  object = "channel_bed"
  object = "channel_bed_grain"
  object = "channel_bed_surface"
  object = "channel_centerline"
  object = "channel_cross_section"
  object = "channel_inflow_end"
  object = "channel_outflow_end"
  object = "channel_suspended_sediment_in_water"
  object = "channel_water"
  object = "channel_water_surface"

  Examples

channel__bankfull_width
channel__downstream_hydraulic_geometry_depth_vs_discharge_exponent
channel__downstream_hydraulic_geometry_slope_vs_discharge_coefficient
channel__station_hydraulic_geometry_width_vs_discharge_exponent
channel__meander_amplitude
channel__meander_curvature_radius
channel__meander_wavelength

channel_bed__manning_coefficient
channel_bed__relative_roughness_ratio     (a dimensionless ratio)
channel_bed__roughness_length
channel_bed__shear_stress
 
channel_bed_grain__d50_diameter
channel_bed_grain__d84_diameter

channel_bed_surface__cross_stream_slope
channel_bed_surface__downstream_slope
 
### channel__bed_roughness_length_to_water_depth_ratio    ????
 
channel_bed_water__hydrostatic_pressure
channel_bed_water__pressure
 
channel_centerline__length
channel_centerline__straight_sinuosity
channel_centerline__valley_sinuosity

channel_cross_section__area
channel_cross_section__hydraulic_radius
channel_cross_section__max_of_depth
channel_cross_section__perimeter
channel_cross_section__top_width
channel_cross_section_trapezoid__bank_angle
channel_cross_section_trapezoid__bottom_width
channel_cross_section__wetted_area
channel_cross_section__wetted_perimeter
channel_cross_section__width_to_depth_ratio

channel_inflow_end__elevation
channel_inflow_end__latitude
channel_inflow_end__specific_contributing_area
channel_inflow_end__total_contributing_area    (or drainage area ?)

channel_inflow_end_to_outflow_end_elevation_difference  ??

channel_outflow_end__elevation
channel_outflow_end__latitude
channel_outflow_end__specific_contributing_area
channel_outflow_end__total_contributing_area

channel_suspended_sediment_in_water__mass_concentration
 
channel_water__density
channel_water__depth_and_bed_slope_product   # (product is a quantity suffix)
channel_water__fanning_friction_factor
channel_water__froude_number
channel_water__max_of_depth
channel_water__depth
channel_water__shear_stress (anywhere in the channel, vs. at channel_bed)
channel_water__speed 
channel_water__pressure     (anywhere in the channel vs. at channel_bed)
channel_water__temperature
channel_water__volume
channel_water__volume_inflow_rate
channel_water__volume_outflow_rate   (volume_outflow_rate vs. "discharge" ?)
 
channel_water_surface__cross_stream_slope
channel_water_surface__downstream_slope

• If we use "volume_inflow_rate" and "volume_outflow_rate" instead of discharge, then we'll also need to use "unit_width_volume_outflow_rate", etc.

• Note that "inflow_end" and "outflow_end" are used instead of "high_end" and "low_end" because it is possible for the "outflow end" to be the "high end".

• Instead of "channel_inflow_end__contributing_area", we could use: "channel_inflow_end_watershed__area". There are several different methods for computing contributing area (or drainage area) and the method should be indicated using an <assume> tag in a Model Metadata File, such as "d8_flow_direction_method", "d_infinity_flow_direction_method" or "mass_flux_flow_direction_method".

• It would be nice to have a short, unambiguous standard name for:
  channel_inflow_end_to_outflow_end__elevation_difference.
  Perhaps we could introduce "drop" as a quantity suffix (like increment and step) for this purpose, but this doesn't capture the end-to-end aspect of the drop.

• Note that "channel_bank_angle" by itself would be ambiguous; is it the angle the bank makes with the vertical z-axis or with a horizontal x-axis? However, "channel_cross_section_trapezoid_bank_angle" is clear.

• A quantity like "bottom_width" or "bank_angle" may only be well-defined for cross-sections of a particular shape, like a trapezoid. In such cases we use the Object_name + model_name Pattern.

• Avoid inserting the word "mean" or "average" for quantities like "depth" and "speed". Assumptions or clarifications on how quantities are computed are provided using <assume> tags in an associated Model Metadata File.

• We talk of "channel_networks", but the network is not part of the channel.

• An outlet would be considered part of a watershed and not part of a channel. See the object pattern for Watershed, Basins and Catchments.

Attributes of Earthquakes

  quantity = attribute

  Examples

earthquake_release_energy        #####
earthquake_epicenter_latitude
earthquake_mercali_intensity
earthquake_moment_magnitude
earthquake_richter_magnitude
earthquake_p_wave_amplitude
earthquake_p_wave_wavelength
earthquake_surface_wave_scale

• There are many types of Seismic waves, including: P-waves, Rayleigh waves,S-waves and http://en.wikipedia.org/wiki/Stoneley_wave Stonely waves].

• See: Bulk modulus, Compressibility, Elastic modulus, Shear modulus, Stiffness and Young's modulus.

• See: Earthquake, Epicenter, Mercali intensity scale and Richter scale.

Attributes of Glaciers

  quantity = attribute

  Examples

glacier_ablation_zone__area
glacier_ablation_zone__area_fraction   (or ablation_zone_to_total_area_fraction ?)
glacier_accumulation_zone__area
glacier_accumulation_zone__area_fraction
glacier__area
glacier_bed__pressure
glacier_bed__shear_stress
glacier_bed__sliding_speed
glacier_bed_surface__slope       (See: Surface template.)
glacier__calving_rate
glacier__cumulative_meltwater_volume  #####
glacier__derivative_wrt_time_of_thickness
glacier__downward_eastward_shear_stress_component
glacier__eastward_velocity_component
glacier__emissivity
glacier_equilibrium_line__altitude
glacier__flow_speed
glacier__internal_temperature
glacier__melt_rate
glacier_model__glen_law_exponent    #### (or "creep_exponent" ?)
glacier_model__glen_law_parameter   #### (or "creep_parameter" ?)
glacier__retreat_rate      (See: Glacier retreat; perhaps a terminus speed)
glacier__thickness
glacier_top_surface__slope       (see glacier_bed_surface_slope)
glacier_top__temperature
glacier__volume
glacier__x_axis_velocity_component

• In glaciology, "mass_balance" has a specific meaning that can be confusing to scientists from other disciplines. See: Glacier mass balance. It is the difference between accumulation and ablation (melting and sublimation) and therefore the net rate at which ice is being "added" to the glacier. Perhaps a quantity name such as: "glacier__derivative_wrt_time_of_thickness" would be more consistent with other standard names.

• Within the CSDMS Standard Names, quantity names "altitude" and "elevation" are taken to have distinct meanings. See Altitude and Elevation. However, the quantity name equilibrium_line_altitude is allowed since it is a standard term in glaciology and otherwise follows the naming rules.

• Note that these names don't contain the word "ice", since a glacier is a persistent body of ice (by definition) and including "ice" is therefore redundant. However, for a glacier on another planet (e.g. Mars) that is not made of water, an adjective such as "carbon_dioxide" can be inserted before "glacier". In fact, this is the trend in the current literature.

• We may need an additional adjective before "area" in order to distinguish between a "surface area" and "projected area".

• See: Accumulation zone, Ablation zone, Glacier, Ice sheet, Meltwater and Glacier terminus.

Attributes of Molecules

  quantity = attribute
  quantity = "bond_angle"
  quantity = "bond_dissociation_energy"
  quantity = "bond_energy"
  quantity = "bond_length"
  quantity = "proton_number" (total number of protons)
  quantity = "torsion_angle"
  quantity = "vibration_frequency"

Examples

water_molecule_actual_bond_angle
water_molecule_ideal_bond_angle  (or replace "ideal" by "VSEPR" ?)
water_molecule_hydrogen_number  (??? number of hydrogen atoms)
water_molecule_h_o_bond_dissociation_energy
water_molecule_h_o_bond_length
water_molecule_h_o_h_bond_angle

• A molecule is an electrically neutral group of two or more atoms held together by covalent chemical bonds.

• CSDMS Standard Names allow using the standard symbol for atoms of a particular element that occur in a molecule (but in lower case).

• There is distinction between "bond energy" and "bond dissociation energy".

• It seems that the bond energy, bond dissociation energy and bond length all depend on the molecule that the atoms are in and not just which two types of atoms are involved. If this is the case, then names should use the Part-of-another-Object Pattern (and perhaps the Object-to-object Quantity Pattern for the atoms), as in: "water_molecule_h_o_bond_length" and "water_molecule_h_o_bond_dissociation_energy".

• See: bond length, bond-dissociation energy and bond energy.

• Bond angles and lengths in molecules are defined as time averages.

• A bond_angle can be defined for 2 consecutive bonds and 3 atoms, as in "water_molecule_bond_angle" or "water_molecule_h_o_h_bond_angle". For a molecule in which all bond angles are the same, like benzene, we could have "benzene_c_c_c_bond_angle" or "benzene_c_c_h_bond_angle". See: Benzene.

• A torsion_angle can be defined for 3 consecutive bonds and 4 atoms, as in "ethane_h_c_c_h_torsion_angle". A synonym is "dihedral_angle".

• For ligands, a ligand cone angle and ligand bite angle can be defined.

• Valence shell electron pair repulsion theory (VSEPR) is a model in chemistry used to predict the shapes of molecules, such as "ideal bond angles".

• Molecules have "vibration frequencies" associated with all the different ways in which the atoms in the molecule can undergo a periodic motion relative to one another. (These relative positions don't change when the molecule rotates or translates as a whole.) See: Molecular vibration. (Individual atoms don't have vibration frequencies but they do have "emission frequencies".) In the so-called: rocking, scissoring, twisting and wagging vibrations, the bond lengths between atoms don't change. In stretching vibrations (symmetric or antisymmetric), the bond lengths change. For the CSDMS standard names we may be able to use names such as "ethylene_wagging_vibration_frequency".

• We could use "hydrogen_number" to quantify the number of hydrogen atoms in a molecule, but that term is also used in a medical context to mean the quantity of hydrogen that 1 gram of fat will absorb.

Attributes of Planets

  quantity = attribute

  Examples

earth_axis_tilt_angle     (see "Object vs. Adjective Rule")
earth_ellipsoid_equatorial_radius
earth_ellipsoid_flattening_ratio
earth_ellipsoid_polar_radius
earth_mass
earth_orbit_eccentricity        (see "Object vs. Adjective Rule")
earth_rotation_rate
earth_rotation_period      (see "Process_name + Quantity Pattern")
earth_sidereal_day
earth_solar_irradiation_constant    ( or just "solar constant"?  See notes.)
earth_standard_gravity_constant    (see the Constant template)
mars_mean_diameter
mercury_axis_precession_period
mercury_axis_precession_rate
venus_orbit_inclination_angle  (or "venus_orbit_to_ecliptic" ?)

• Some of these are needed for proper georeferencing or modeling solar radiation via celestial mechanics.

• Notice that the word "ellipsoid" was inserted in three examples above. This is an example of the Object_name + Model_name pattern that is explained at the top of the document: CSDMS Object Templates.

• See: Orbital elements for a discussion of the 6 parameters (including "inclination angle") that uniquely specify a specific orbit in astronomy.

• Note that Insolation refers to the solar irradiance measured at a given location on Earth, typically around 1000 W/m^2. The Solar irradiation constant is measured at the outer surface of Earth's atmosphere and is roughly 1366 W/m^2. Due to scattering and absorption in the atmosphere, the "insolation" is less than the "solar irradiation constant".

• See: Axial precession, Axial tilt, Declination, Ecliptic, Nutation, Position of the Sun, Precession, Right ascension, Solar azimuth angle, Solar elevation angle and Zenith.

Attributes of Processes

• See the template for Process Attributes.

Attributes of Products of a Company

  quantity = attribute

• See the CSDMS Object Template for "Product of a Company".

Attributes of Radiation

  quantity = attribute
  quantity = "absorbance"
  quantity = "albedo"
  quantity = "amplitude"
  quantity = "emission_angle"
  quantity = "emissivity"
  quantity = "flux"
  quantity = "frequency"
  quantity = "incidence_angle"
  quantity = "intensity"
  quantity = "period"
  quantity = "reflectivity"
  quantity = "standad_refraction_index"
  quantity = "transmittance"

• Albedo is also called "diffuse reflectivity" or "reflectance coefficient".

• Note that "refraction_index" is an example of a quantity that really requires two objects to be specified, electromagnetic radiation or light of a particular wavelength and the medium that it is traveling through (e.g. air, water, vacuum). However, standard refractive index measurements (see List of refractive indices) are taken at the yellow doublet sodium D line, with a wavelength of 589 nanometers. So in CSDMS standard names the insertion of the adjective "standard" means that only one object, the medium, needs to be specified. So "air_standard_refraction_index" would be a valid and unambiguous name, but 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".) We may also want to allow names such as "550_nm_light_in_air_refraction_index".

• See: Absorbance, Albedo, Amplitude, Electromagnetic radiation, Frequency,Intensity in physics,Reflectivity, Refraction index, Transmittance, Visible radiation and Wavelength.

Attributes of Sea Ice

  quantity = attribute

  Examples

sea_ice_age
sea_ice_area
sea_ice_area_fraction   (vs. "sea_ice_concentration"; see Concentration)
sea_ice_emissivity
sea_ice_extent
sea_ice_thickness
sea_ice_volume

• What about "sea_ice_mass_balance" ? The term "mass_balance" is also used in glaciology but is confusing outside of that domain.

• The quantity "sea_ice_extent" is related to "sea_ice_area" but involves a "reference threshold" (as a percentage, usually 15%) that must be specified with an <assume> tag in a Model Metadata File. See Measurement of sea ice. Also see Reference Quantities.

• See Concentration, Fraction and Thickness.

Attributes of Topography

  quantity = attribute
  quantity = "aspect_angle" (aspect is not used by itself)
  quantity = "elevation"
  quantity = "laplacian_curvature"
  quantity = "mean_curvature"
  quantity = "plan_curvature"
  quantity = "profile_curvature"
  quantity = "slope" [unitless = rise/run = L/L]
  quantity = "slope_angle" [radians or degrees]
  quantity = "specific_contributing_area"
  quantity = "streamline_curvature"
  quantity = "tangential_curvature"
  quantity = "total_contributing_area"

  Examples

bedrock_surface__elevation
glacier_surface__slope
ground_water_table_surface__aspect_angle
land_surface__derivative_wrt_time_of_elevation
land_surface__derivative_wrt_x_of_elevation
land_surface__profile_curvature
sea_water_surface__mean_curvature

• Note that many of these quantities are defined in terms of first or second derivatives, which requires a certain degree of smoothness (differentiable or twice differentiable). Real topography is generally not this smooth, especially at small scales, but these quantities are nevertheless useful and can be computed from DEMs. In the CSDMS Standard Names, the Object_name + Model_name Pattern indicates that the word "surface" should be inserted in front of the quantity name when the quantity is only defined for some kind of idealized "model" surface. See the Surface template.

• "Specific contributing area" (SCA) is a quantity that can be defined for each point on a mathematical surface as the (upstream) contributing area per unit contour length. "Total contributing area" (TCA) is a quantity obtained from integrating SCA over a line segment, such as the width of a grid cell projected in the direction of the surface gradient. The relationship between TCA and SCA is similar to that between water discharge (Q) and unit-width water discharge (q).

• "contour curvature" is a synonym for "plan curvature". "streamline curvature" is not well-known. See: Peckham (2011).

• See: Aspect, Bathymetry, Curvature, Drainage basin, Elevation, Geomorphometry, Slope and Topography.

• There is an international society called: geomorphometry.org that meets every two years.

Capacity

  base_quantity = "capacity"
  base_quantity = "carrying_capacity"
  base_quantity = "thermal_capacity"

  Examples

air_thermal_capacity
aluminum_specific_thermal_capacity
earth_human_carrying_capacity    (need to specify two objects ??)
iron_thermal_capacity
snow_thermal_capacity
soil_thermal_capacity

• The more general quantity "thermal_capacity" is used instead of "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 thermal 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. See: Carrying capacity.

• Other quantities that contain "capacity" are: battery capacity, channel capacity and combining capacity.

• 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.

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.

Code

  base_quantity = "code"

  Examples

location_postal_code     (See: Postal code.)
watershed_pfafstetter_code
watershed_usgs_hydrologic_unit_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

iron__thermal_expansion_coefficient
channel_bed__manning_coefficient
math__binomial_coefficient     (See Constants in Math)
polynomial__leading_coefficient
rubber_on_concrete__kinetic_friction_coefficient
rubber_on_pavement__static_friction_coefficient
salt_in_water__diffusion_coefficient   ####

• Note that some of these use the Object-in-object Quantity Pattern and many others use the Process_name + Quantity Pattern (e.g. "expansion_coefficient").

• Coefficients often occur in empirical laws, usually as multiplicative factors.

• A "bulk exchange coefficient" for water vapor or heat (in the atmosphere?) is sometimes used, with units of [length / time]. (Is this a synonym for a more commonly used term?)

• "Manning's coefficient" is sometimes called "Manning's roughness coefficient" or "Manning's roughness parameter" or something similar. The word "roughness" is not needed to remove ambiguity, however.

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

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

• See Friction.

Component

  quantity_suffix = "component"
  quantity = [ direction adjective ] + [ vector quantity ] + "_component"

  Examples

atmosphere_eastward_velocity_component
atmosphere_northward_vorticity_component
channel_water_x_axis_velocity_component
sea_water_downward_eastward_shear_stress_component

• This is a quantity suffix that creates a new quantity from an existing base quantity (like a vector or tensor). See Anomaly, Increment and Magnitude.

• Note that "x_axis_" is used instead of just "x_". It might be interesting (and seems consistent) to introduce a word like "xward".

• We could also use the pattern:
    quantity = [ vector quantity ] + [ direction ] + "_component"
  but the above pattern seems preferable.

• See Stress, Velocity and Vorticity.

Concentration

  base_quantity = "concentration"
  quantity = "mass_concentration" [kg m-3]
  quantity = "molar_concentration" [mol m-3] (molarity)
  quantity = "number_concentration" [m-3]
  quantity = "volume_concentration" [1] = [m3 / m3]

  Examples

channel_suspended_sediment_in_water_mass_concentration
magnesium_chloride_in_sea_water_molar_concentration
suspended_sediment_in_sea_water_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 ratio 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.

Conductivity

  base_quantity = "conductivity"
  quantity = "electrical_conductivity" [siemens m-1] or [ohm-1 m-1]
  quantity = "hydraulic_conductivity" [m s-1]
  quantity = "ionic_conductivity"
  quantity = "thermal_conductivity" [W m-1 K-1]

  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"
  quantity = "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

avogadro_constant           [unit mol-1]   (see Note below)
boltzmann_constant         (See ideal_gas_constant)
cosmological_constant       [m-2]   (about 10^{-52};  object = universe)
coulomb_constant            [N m2 C-2]     (C = Coulomb SI unit)
dielectric_constant         [1]            (can be complex; = static_relative_permittivity)
fine_structure_constant     [1]            (about 1/137.035999074)
ideal_gas_constant          [J mol-1 K-1]   (R = 8.3144621)
latent_heat_fusion_constant [J kg-1]       (similar for vaporization)
light_speed_constant        [m s-1]
planck_constant             [J s]
rydberg_constant            [m-1]
solar_constant              [W m-2]        (solar_irradiation_constant may be better)
spring_constant             [kg s-2]       (in Hooke's Law)
standard_gravity_constant   [m s-2]  ("little g", see Attributes of Planets template)
stefan_boltzmann_constant   [W m-2 K-4]
universal_gravitation_constant   [m3 kg-1 s-2]  ("big G", from Newton's law)
von_karman_constant         [1]

• Although "latent heat of fusion" and "latent heat of vaporization" are constants for a given substance (e.g. water), it may be better to treat "latent_heat" as a quantity name and use the naming pattern: "water__fusion_latent_heat" and "water__vaporization_latent_heat". This would then conform to the Process_name + Quantity Pattern. See: 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.

• If there is no naturally-associated object, we could use a placeholder object name like "physics".

• 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.

• See: Boltzmann constant,Coulomb constant, Fine-structure constant,Ideal gas constant,Planck constant,Psychrometric constant,Rydberg constant,Stefan-Boltzmann constant, Universal gravitational constant and von Karman constant.

Content

  base_quantity = "content"
  quantity = "energy_content"
  quantity = "mass_content"
  quantity = "water_content"

  Examples

coal_thermal_energy_content
dry_wood_thermal_energy_content
gas_thermal_energy_content
 
soil_field_capacity_water_content
soil_hygroscopic_water_content
soil_initial_water_content
soil_normalized_water_content  (also called "effective saturation")
soil_residual_water_content
soil_saturated_water_content
soil_wilting_point_water_content
 
snow_cold_content  ? (must be overcome before melting starts to occur)
snow_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. While "soil_water_content" is a fairly standard term in hydrology, it would be perfectly valid and perhaps more clear to use the term "water_in_soil_volume_fraction".

• The quantity "thermal_energy_content" can be applied to substances like air and snow but is often used in the context of fuels like coal, gas and wood.

• In CF Standard Names, "content" indicates a quantity per unit area. However, in infiltration theory, "soil_water_content" is a "volume_fraction". CF has "soil_moisture_content", "soil_moisture_content_at_field_capacity" and "soil_carbon_content". See Water Content.

• Do we want to distinguish between: gravimetric_water_content and volumetric_water_content ?

• Many CF Convention 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.

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"
  quantity = "blood_cell_count"

  Examples

channel_bed_wolman_pebble_count
human_platelet_count
human_red_blood_cell_count
human_white_blood_cell_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.

• The "Wolman pebble count" due to M. Gordon "Reds" Wolman is sometimes used in river hydraulics and sediment transport.

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

• The number of occurrences of a given event may also be called a "count".

• See Count data and the Number template.

Curvature

• See the Attributes of Topography template which lists several types of curvature. However, curvature can also be defined for curves, such as coastline curves and space curves (or trajectories).

Density

  base_quantity = "density"

  Examples

air_density
air_stp_density   (stp = standard temperature and pressure)
friedmann_universe_critical_density
sea_water_density
watershed_drainage_density

• Maybe expand this to "mass_density" to avoid any ambiguity. Units for "mass_density" would always be [kg m-3]. Consider cases like: "drainage_density" [L-1]

• The adjective "bulk" is often inserted before density.

• Physicists sometimes use the term "flux_density".

• Hydrologists use the term "drainage_density", which is defined as the total length of channels in a watershed divided by the watershed area. Similarly, "source_density" refers to the total number of sources (i.e. channel heads) in a watershed divided by the watershed area.

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

• See Energy density, Power density and Surface power density.

Depth

  base_quantity = "depth"
  quantity = "precipitable_depth"
  quantity = "secchi_depth"

  Examples

channel_water_mean_depth  ??
ground_water_table_depth
sea_water_depth  (or sea_floor_depth ?? #######)
sea_water_secchi_depth
water_vapor_in_vertical_air_column__precipitable_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". However, the terms "precipitable water depth" and "precipitable depth of water vapor" are also used and imply units of length. An unambiguous standard name for this quantity might be: "water_vapor_in_vertical_air_column__precipitable_depth", which uses the Object-in-object Quantity Pattern.

• See Altitude, Elevation, Height and Thickness.

Diameter

  base_quantity = "diameter"

  Examples

bluejack_oak_tree_trunk_diameter
crater_circle_diameter      (see Object_name + model_name Pattern)
rooted_tree_graph_diameter
square_diameter
watershed_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"
  quantity = "magnetic_diffusivity" [m2 s-1]
  quantity = "mass_diffusivity" [m2 s-1]
  quantity = "momentum_diffusivity" [m2 s-1] (nickname for kinematic_viscosity)
  quantity = "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"
  quantity = "box_counting_dimension"
  quantity = "hausdorff_dimension"
  quantity = "hausdorff_dimension"

  Examples

cantor_set_hausdorff_dimension
peano_curve_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

  quantity = [ famous person's name ] + "_number"

  Examples

airplane__mach_number
channel_water__reynolds_number
channel_water__froude_number
heat_equation__courant_number   #### (insert "model" ??)
helium_plume_in_air__richardson_number  ### (vs. helium_in_air_plume_)
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

  base_quantity = "discharge"
  quantity = "unit_width_discharge"
  quantity = "volume_inflow_rate"
  quantity = "voume_outflow_rate"

  Examples

channel_water__discharge [m3 s-1]
watershed_outlet_water__discharge [m3 s-1]

• Units are [m3 s-1] and typical notation is "Q".

• 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 volume_inflow_rate and volume_outflow_rate are always unambiguous and may therefore be preferable in the current context. Possible constructions: "lake_water_volume_inflow_rate" or "channel_reach_water_unit_length_volume_inflow_rate" (for "lateral inflow rate").

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

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

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

• 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 units of [m2 s-1].

• If a "sediment discharge" quantity has units of [mass / time], then it should be called something like "sediment_in_water_mass_flow_rate" instead of "sediment_in_water_discharge", since discharge has units of [volume / time].

Distance

  base_quantity = "distance"

  Examples

channel_end_to_end_straight_distance    #####
earth_to_sun_mean_distance
particle_to_sea_floor_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".

Duration

  base_quantity = "duration"

  Examples

sunshine_duration
water_precipitation_duration   (vs. "rainfall_duration")

• See the Precipitation section.

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

Elevation

  base_quantity = "elevation"

  Examples

bedrock_surface_elevation
ground_water_table_surface_elevation
land_surface_elevation
sea_surface_elevation

• The word "altitude" is reserved for objects that are above and not in contact with the land surface. (e.g. aircraft, air parcel, balloon)

• 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.

Energy

  base_quantity = "energy"
  quantity = "electric_energy"
  quantity = "free_energy"
  quantity = "internal_energy"
  quantity = "kinetic_energy"
  quantity = "potential_energy"
  quantity = "specific_energy"
  quantity = "thermal_energy"

  Examples

ball_potential_energy
turbulence_kinetic_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

glacier_model__glen_law_exponent
sediment_transport_law_slope_exponent  ?? ##########
watershed_model__flint_law_exponent
watershed_model__hack_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

particle_cunningham_correction_factor
oscillator_q_factor
pipe_water_darcy_weisbach_friction_factor  (same as moody_friction_factor)
pipe_water_fanning_friction_factor
sine_wave_crest_factor
sun_protection_factor

• Use "manning_roughness_coefficient" 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".

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

• See: Atomic form factor (or atomic scattering factor), Crest factor, Q factor, Sun Protection Factor (SPF) and View factor.

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

Flag

  base_quantity = "flag"

  Examples

None yet.

• 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).

Flux of Heat or Energy

  base_quantity = "flux"

• "Flux" can be viewed as "surface bombardment rate". See the Wikipedia article on "Flux".

• In CF Standard Names, "flux" implies per unit area. They say that "flux_density" is used in physics instead.

• In 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 "heat", "longwave", "shortwave" and "radiative".

• Most energy fluxes in atmospheric models have units of [W m-2] (i.e. energy per unit area and per unit time).

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

Flux of Mass

  quantity = "mass_flux"

• In CF Standard Names, units are [kg m-2 s-1].

• See Concentrations, Discharges.

Flux of Momentum

  quantity = "momentum_flux"

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

• In CF Standard Names, units are [Pa].

Fraction

  quantity_suffix = "fraction"
  quantity = "area_fraction"
  quantity = "mass_fraction"
  quantity = "mole_fraction"
  quantity = "time_fraction"
  quantity = "volume_fraction"

  Examples

agricultural_land__area_fraction
arable_land__area_fraction
burned_land_area_fraction
clouded_land__area_fraction
farmed_land__area_fraction
flooded_land__area_fraction
forested_land__area_fraction
glaciated_land__area_fraction      (or "ice_covered_land__area_fraction" ?)
grazing_land__area_fraction
irrigated_land__area_fraction
lake_covered_land__area_fraction          (uses "covered")
land_vs_water__area_fraction
private_land__area_fraction
public_land__area_fraction
sea_water_vs_land__area_fraction       (could start with prefix "earth_")
snow_covered_land__area_fraction       (uses "covered")
urban_land__area_fraction
vegetated_land__area_fraction
water_vs_land__area_fraction
watershed_forested_land__area_fraction
wetland_covered_land__area_fraction        (uses "covered")
 
rocket_payload__mass_fraction
rocket_propellant__mass_fraction  (See: Propellant mass fraction.)
 
clay_in_soil_volume_fraction   (using object_in_object pattern)
sand_in_soil_volume_fraction
silt_in_soil_volume_fraction
 
frozen_water_in_soil_volume_fraction   (modified from CF name below)
oxygen_in_sea_water_volume_fraction  (modified from CF name below)

• It appears that "fraction" should be viewed as a quantity suffix 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.

• 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. A hyphen in a hyphenated adjective like "snow-covered" is converted to an underscore.

• If an "area fraction" variable name is meant to distinguish between two possible states, such as land and water, then the reserved word "vs" can be used in a construction like: "land_vs_water__area_fraction". Or should we just use: "dry_land__area_fraction"?

• 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 watershed, then constructions like: "watershed_forested_land__area_fraction" can be used and conform to the Part of Another Object Pattern.

• 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 "water_in_soil_volume_fraction" instead would be consistent with the Object-in-object Quantity Pattern.

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.)
manning_roughness_coefficient
mean_roughness_length   ("z0" for law of the wall)
shear_stress   (See the Stress template.)
static_friction_coefficient

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

Frequency

  base_quantity = "frequency" [1/second]
  quantity = "angular_frequency" [radians/second]

  Examples

cesium_atom_characteristic_emission_frequency
sea_water_brunt_vaisala_frequency   (also called "buoyancy_frequency")
sea_water_surface_wave_frequency

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

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

• See Wikipedia: Brunt–Väisälä frequency.

• See Normalized frequency, Nyquist frequency.

Fuel Efficiency

  quantity = "fuel_consumption_rate" ["gallons per mile" or "liters per km"]
  quantity = "fuel_economy" ["miles per gallon" or "km per liter"]
  quantity = "fuel_specific_energy_content" [Joules / kg]

  Examples

automobile_fuel_consumption_rate
automobile_fuel_economy
gm_hummer_fuel_consumption_rate
toyota_corolla_fuel_economy

• 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.

Head

  base_quantity = "head"
  quantity = "friction_head"
  quantity = "hydraulic_head"
  quantity = "pressure_head"
  quantity = "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"
  quantity = "latent_heat"
  quantity = "sensible_heat"

  Examples

water__fusion_specific_latent_heat          (334 [kJ kg-1])
water__vaporization_specific_latent_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 examples 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"
  quantity = "geopotential_height"
  quantity = "reference_height"

  Examples

empire_state_building_height
bluejack_oak_tree_mean_height
human_mean_height

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

• See Reference Quantities.

Humidity and Relative Saturation

  base_quantity = "humidity"
  quantity = "absolute_humidity" (is "volumetric_humidity" a synonym ?)
  quantity = "relative_humidity"
  quantity = "relative_saturation"
  quantity = "specific_humidity"

  Examples

air_relative_humidity   (= water_vapor_in_air_relative_saturation)
carbon_dioxide_in_air_relative_saturation   #### CHECK

• 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.

Increment

  quantity_suffix = "increment"

  Examples

air__pressure_increment
bedrock_surface__elevation_increment
land_surface__elevation_increment

• 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.

• This is a quantity suffix that creates a new quantity from any existing base quantity (e.g. elevation, pressure or temperature). There are many others, including Anomaly, Component, Limit, Magnitude, Ratio and Scale.

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

Index

  base_quantity = "index"

  Examples

diversity_index
normalized_difference_vegetation_index
palmer_drought_severity_index
price_index
soil_moisture_index
standard_refraction_index
wetness_index  (with prefix: soil, topographic, catchment, etc.)

• 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.

Latitude

  base_quantity = "latitude"

  Examples

grid_cell_center_latitude
grid_cell_north_edge_latitude
grid_cell_south_edge_latitude
grid_north_edge_latitude
grid_south_edge_latitude

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

• Typical units are "decimal degrees".

• The adjective "geodetic" may be needed in some cases.

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

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

Limit

  quantity_suffix = "limit"

  Examples

human_hearing_high_frequency_limit    (Note:  hearing is a process name)
neutron_star_tolman_oppenheimer_volkoff_mass_limit
photon_in_human_eye_detection_number_limit    (process_name + quantity)
white_dwarf_star_chandrasekhar_mass_limit

• This is a quantity suffix, similar to Anomaly, Component, Increment and Magnitude. A "limit" is not a quantity by itself and can apply to virtually any quantity.

• Note that the two limits above named after people include the quantity name "mass" after "limit". 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

grid_cell_center_longitude
grid_cell_east_edge_longitude
grid_cell_west_edge_longitude
grid_east_edge_longitude
grid_west_edge_longitude

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

• Typical units are "decimal degrees".

• The adjective "geodetic" may be needed in some cases.

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

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

Magnitude

  quantity_suffix = "magnitude"
  quantity = [ vector quantity ] + "_magnitude"

  Examples

vector_magnitude
normal_stress_magnitude   (or normal_stress_component_magnitude ??)
shear_stress_magnitude
stress_tensor_magnitude ??  #########

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

• Exception: Use "speed" instead of "velocity_magnitude".

• This is a quantity suffix that creates a new quantity from an existing base quantity (like a vector or tensor). Others are Anomaly, Component and Increment.

• In CF Standard Names, "magnitude_of_" is a transformation (prefix) 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. A mask may be 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.

• 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".

• A mask is sometimes associated with a threshold value and "threshold" is a quantity suffix. We could use a standard name like "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 Metadata File.

• A term something like "presence_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

atomic_mass   (also relative_atomic_mass = atomic_weight)
chandrasekhar_limit_mass   (object = white_dwarf_star)
neutron_star_tolman_oppenheimer_volkoff_mass_limit
relativistic_mass
rest_mass (also invariant mass, intrinsic_mass, proper mass)

• The SI units for mass are kilograms.

• What about "biomass"?

• See Attributes of Atoms, Concentration, Flux.

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

Maximum

  Examples

watershed_outlet_water__max_wrt_time_of_discharge   (possibly, 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 watershed discharge. It seems best to introduce "max_wrt_time_of_" and "max_wrt_space_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

None yet.

• 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 watershed discharge. It seems best to introduce "min_wrt_time_of_" and "min_wrt_space_of_" as operations instead. See: CSDMS Operation Templates.

Modulus

  base_quantity = "modulus"
  quantity = "bulk_modulus"
  quantity = "shear_modulus"
  quantity = "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"
  quantity = "julian_day_number"
  quantity = "neutron_number"
  quantity = "protron_number"
  quantity = "quantum_number"
  quantity = "wave_number"
  quantity = "winding_number"

  Examples

carbon_isotope_neutron_number
iron_atom_neutron_number
iron_atom_proton_number
sea_water_surface_wave_number
vehicle_identification_number

• 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. However, dimensionless numbers also end with the word "number" as discussed in the Dimensionless Number template and they are typically not integers. Also the wave number need not be an integer.

• 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

earth_coriolis_parameter
channel_bed_shields_parameter

• Parameters often occur in empirical laws.

• The CSDMS standard names use "manning_roughness_coefficient" vs. "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"
  name = [substance 1] + "_in_" + [substance 2] + "_partial_pressure"

  Examples

carbon_dioxide_in_air_partial_pressure
water_vapor_in_air_partial_pressure
water_vapor_in_air_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:

surface_carbon_dioxide_in_air_and_carbon_dioxide_in_sea_water_partial_pressure_difference
(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

channel_cross_section_perimeter
watershed_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"
  quantity = "orbit_period" (see "Object vs. Adjective Rule")

  Examples

chicken_pox_incubation_period
earth_rotation_period
flood_expected_return_period    ######### Need a flood size adjective.
mars_orbit_sidereal_period
mars_orbit_synodic_period
sea_water_surface_wave_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.

pH

  base_quantity = "ph"

  Examples

acetic_acid_ph
channel_water_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.)

• 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 "void_in_soil_volume_fraction" or maybe "air_in_soil_volume_fraction".

Precipitation

  quantity = "precipitation_" + base_quantity

  Examples

ice__precipitation_rate
methane__precipitation_rate
snow__precipitation_rate
water__precipitation_duration
water__liquid_equivalent_precipitation_rate   (in liquid or solid form)

• 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_rate" has units of [length / time] (e.g. mm 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: "water__liquid_equivalent_precipitation_rate", which 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_rate" and "snow_melt_rate", since the process of melting converts ice and snow to liquid water.

• The name "snow__liquid_equivalent_depth" is also used and is computed by multiplying the "snow_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

channel_bed_water_hydrostatic_pressure
channel_bed_water_pressure  
channel_water_pressure       (anywhere in the channel)
earth_atmosphere_pressure
    (also: earth_atmosphere_at_land_surface_pressure ??)

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

• 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.

• Note that additional assumptions like "equilibrium" and "hydrostatic" could be left out of the name and instead provided using an <assume> tag in the metadata file, but they are currently allowed as modifiers in the quantity name also.

• 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 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. Our "object-in-object" pattern therefore prescribes using: "water_vapor_in_air_partial_pressure" instead of just "air_vapor_pressure". See Vapor 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.

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

Process Attributes

  quantity = [ process name ] + [ base_quantity ]

  Examples

digestion_period, gestation_period, hibernation_period,
incubation_period, sleeping_period
-------------------------------------------------------------------
infiltration_rate, lapse_rate, melt_rate, precipitation_rate,
rainfall_rate  (use precipitation instead?)
    (Note:  "melt" -> "melting" ?)
-------------------------------------------------------------------
conception_date
delivery_date        (vs. "expected_delivery_date" or "due_date")
launch_date
ovulation_date
starting_date        (or "start_date" ??)
----------------------
rainfall_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

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

• The base quantity "_rate" makes sense for most processes, but a given process if often naturally associated with other base quantities.

• 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")

• See the Rates of Processes template for examples where the base quantity is "rate".

Radiation

  quantity = "radiation_" + quantity

  Examples

air_net_downward_shortwave_radiation_flux
incandescent_light_bulb_radiation_intensity   ? ##### CHECK
universe_cosmic_background_radiation_frequency

• Note that "radiation" is a process and not a quantity by itself. Quantity names can be constructed using the Process_name + Quantity Pattern. See the Process Attributes template.

• 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 typically have units of [W m-2]. See the Flux template.

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 Schwarzchild Radius , Turning Radius and Minimum Railway Curve Radius.

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

Rates of Processes

  quantity = [ process name ] + "_rate"

  Examples

air_temperature_lapse_rate
alcohol_consumption_rate
fuel_consumption_rate
ice_precipitation_rate
liquid_methane_precipitation_rate   (on Titan)
snow_precipitation_rate
surface_snow_melt_rate        ("melt" -> "melting" ??)
surface_water_evaporation_rate
surface_water_infiltration_rate
water_precipitation_rate

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

• Note that "precipitation_rate" follows the Process_name + Quantity Pattern and is used in the examples instead of "icefall_rate", "rainfall_rate" and "snowfall_rate". 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 and the CSDMS Process Names.

Ratio

  base_quantity = "ratio"
  quantity_suffix = "ratio" (in some cases)
  quantity = "aspect_ratio"
  quantity = "mass_ratio"

  Examples

air_to_fuel_mass_ratio     (or "mixture_ratio")
[ animal ] + brain_to_body_mass_ratio
earth_ellipsoid_inverse_flattening_ratio
fuel_to_oxidizer_equivalence_ratio   ###
image_aspect_ratio
lithosphere__poisson_ratio
rocket_to_payload_mass_ratio
rocket_to_propellant_mass_ratio
 
channel_cross_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

  quantity = "reference_" + quantity1 + "_" + quantity2
  quantity = quantity1 + "_reference_" + quantity2

  Examples

air__standard_refraction_index
 
wind__reference_height_speed
wind__speed_reference_height    ("reference" is between the quantities)
 
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.

Scale

  quantity_suffix = "scale"
  quantity = "length_scale"
  quantity = "time_scale"
  quantity = "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"
  quantity = "straight_sinuosity"
  quantity = "valley_sinuosity"

  Examples

channel_centerline__straight_sinuosity
channel_centerline__valley_sinuosity
valley_centerline__straight_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 call "valley 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. An alternative, which we call "straight sinuosity", 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 "straight sinuosity" will always be greater than or equal to "valley 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".

• See: Sinuosity, Tortuosity, Chord, Geodesic and Meander.

Solubility

  base_quantity = "solubility"

  Examples

carbon_dioxide_in_water_solubility
diethyl_ether_in_water_solubility
ethanol_in_water_solubility

• This quantity always involves two substances and therefore requires using the Object-in-object Quantity Pattern. 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_max_life_span 

• 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"
  quantity = "escape_speed"
  quantity = "flow_speed"
  quantity = "settling_speed"
  quantity = "terminal_speed"

  Examples

channel_water_flow_speed
glacier_bed_sliding_speed
wind_speed

• The quantity name "speed" is equivalent to "velocity_magnitude". Velocity components use the Component template (e.g. glacier_eastward_velocity_component).

• When applied to fluids, the process name "flow" is inserted in accordance with the Process_name + Quantity Pattern.

• "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.

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

Step

  quantity_suffix = "step"

  Examples

channel_water_model__time_step

• This is another quantity suffix 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.

Stress

  base_quantity = "stress"
  quantity = "deviatoric_stress"
  quantity = "normal_stress"
  quantity = "shear_stress" (vs. "shearing_stress"; see below)

  Examples

channel_bed_shear_stress
channel_bed_shields_critical_shear_stress
sea_floor_surface_normal_stress
sea_floor_surface_x_z_shear_stress_component
sea_water_downward_eastward_shear_stress_component
sea_water_downward_northward_shear_stress_component

• For models that use a geographic coordinate system, we would use "eastward", "northward" and "upward" to describe component directions. For models that use a Cartesian (or equal-area) coordinate system, we would use "x", "y" and "z". But perhaps we should use "xward" or "x_axis" instead ?

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

• Note that a quantity suffix like "component" or "magnitude" may be inserted after the word "stress" when it removes ambiguity. Absence of the suffix implies magnitude.

• 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.

• 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 definitions of "critical_shear_stress" by future researchers.

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

• There are 19 CF Convention 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"
  quantity = "potential_temperature"

  Examples

iron_melting_point_temperature
snow_temperature
soil_temperature
water_boiling_point_temperature
water_freezing_point_temperature
water_vapor_in_air_bubble_point_temperature
water_vapor_in_air_dew_point_temperature
water_vapor_in_air_frost_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 assumptions in metadata.

• 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, Potential temperature, Effective temperature, Color temperature, Brightness temperature, Atmospheric temperature, Dry-bulb temperature and Wet-bulb temperature.

Term

  base_quantity = "term"
  quantity = "acceleration_term"
  quantity = "convection_term"
  quantity = "diffusion_term"
  quantity = "forcing_term"
  quantity = "friction_loss_term"
  quantity = "sink_term"
  quantity = "source_term"
  quantity = "time_derivative_term" (or use "unsteady_term" instead?)

  Examples

convection_diffusion_equation_convection_term"
convection_diffusion_equation_diffusion_term"
navier_stokes_equation_body_force_term
navier_stokes_equation_convective_acceleration_term
navier_stokes_equation_pressure_gradient_term
navier_stokes_equation_unsteady_acceleration_term
navier_stokes_equation_viscosity_term    (or "viscous_diffusion_term" ?)
poisson_equation_laplacian_term
poisson_equation_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

burgess_shale_stratum_thickness    ("stratum" or "layer" ?)
human_hair_thickness
mars_atmosphere_thickness
paper_thickness
snow_layer_thickness
soil_layer_0_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

  quantity_suffix = "threshold"

• This is a quantity suffix that could be used with any base quantity and is not a quantity by itself.

• 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_reach_peak_outgoing_water_discharge_time
earth_location_for_mars_rising_time

• The quantity "time" can refer to the specific time associated with an event, such as "mars_rising_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 "rising_time" and "setting_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"
  quantity = "time_step"

  Examples

channel_water_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.

Unit-width Quantity

  quantity = "unit_width_" + base_quantity

  Examples

land_surface_water__unit_width_discharge

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

• What about "power_per_unit_length_of_wave_crest" ?

• "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"
  quantity = "escape_speed"
  quantity = "flow_speed"
  quantity = "settling_speed"
  quantity = "terminal_speed"
  quantity = "velocity_component"

  Examples

ball_in_air_terminal_speed
earth_escape_speed    (vs. escape_velocity)
sand_grain_in_water_settling_speed
sea_water_eastward_velocity_component
sea_water_flow_speed

• 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 quantity suffix component 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". In this case we would need to allow "velocity" itself (a vector) as a base quantity name.

• The shorter quantity name "speed" is used in CSDMS standard names instead of "velocity_magnitude" 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_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 Speed.

Viscosity

  base_quantity = "viscosity"
  quantity = "dynamic_shear_viscosity"
  quantity = "dynamic_volume_viscosity"
  quantity = "eddy_viscosity"
  quantity = "extensional_viscosity"
  quantity = "kinematic_shear_viscosity"
  quantity = "kinematic_volume_viscosity"

  Examples

air_dynamic_shear_viscosity
polymer_extensional_viscosity
sea_water_eddy_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.

• Viscosity depends on temperature, so a reference temperature should be provided with an <assumption> 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 reciprical of viscosity is called fluidity.

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

Voltage

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

  Examples

battery_voltage
electric_appliance_voltage
electric_fence_voltage

• See: Voltage and Voltage drop.

Vorticity

  base_quantity = "vorticity"

  Examples

sea_water_vorticity

• Vorticity is a vector quantity defined as the curl of a fluid velocity (vector) field. When used as a quantity name, it is taken to mean the magnitude of the vorticity vector. The quantity name for a component of the vorticity vector uses the Component template, as in "sea_water_eastward_vorticity_component".

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

• See Vector calculus identities and Vorticity.

Yield

  base_quantity = "yield"
  quantity = "specific_yield" (in groundwater modeling)

  Examples

watershed_sediment_yield

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

• What about "yield_strength" (plastic deformation) ?

• See also: Yield surface.