Model help:TopoFlow-Meteorology

TopoFlow-Meteorology

The module is the meteorology process component for a D8-based, spatial hydrologic model

Model introduction

This component reads a variety of variables for the atmosphere and for the land surface from input files or as simple scalars. It then computes many additional variables, such as vapor pressure, e_air, and net shortwave (solar) radiation, Qn_SW, using built-in [shortwave radiation] and [longwave radiation] calculators that are based on celestial mechanics and widely-used empirical relationships. These additional variables are needed by the Snowmelt → Energy Balance and Evaporation → Energy Balance components. Direct, diffuse and back-scattered radiation fluxes are all modeled. Properties of the atmosphere (e.g. precipitation rate, P, air temperature, T_air, relative humidity, RH, and dust attenuation, γ), are used as well as surface/topographic properties (e.g. slope angle, aspect angle and surface albedo. The approach used here closely follows the one outlined in Appendix E of Dingman (2002). However, instantaneous vs. day-integrated radiation fluxes are used and the optical air mass is modeled using the widely used method of Kasten and Young (1989).

Model parameters

Input 1

Input 2

Input 3

Output 1

Output 2

Parameter	Description	Unit
Components status		Enabled/Disabled
Input directory
Output directory
Site prefix	file prefix for the study site
Case prefix	file prefix for the model scenario
Number of steps	number of time steps
Time step	meteorology time step	sec
ρ H2O type	allowed input types (Scalar/Grid/Time_Series/Grid_Sequence)
ρ H2O	density of water	kg/m3
Cp_air type	allowed input types (Scalar/Grid/Time_Series/Grid_Sequence)
Cp air	heat capacity of air	J/kg/K
ρ_air type:	allowed input types (Scalar/Grid/Time_Series/Grid_Sequence)
ρ air	density of air	kg/m3
Precipitation rates type	allowed input types (Scalar/Grid/Time_Series/Grid_Sequence)
Precipitation rates		mm/yr
PRECIPITATION ONLY toggle	toggle to turn off all variable updates except precipitation

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Uses ports

This will be something that the CSDMS facility will add

Provides ports

This will be something that the CSDMS facility will add

Main equations

• Absolute optical air mass equation

[math]\displaystyle{ m_{abs} \left ( \gamma \right ) = \rho _{0} \int _{0} ^ \infty \left ( \rho / \rho _{0} \right ) \{ 1 - [ 1 + 2 \delta _{0} \left ( 1 - \rho / \rho _{0} \right ) ] \ast [ \cos \gamma / \left ( 1 + h / R \right ) ] ^2 \} ^ {\frac{-1}{2}} dh }[/math]

(1)

[math]\displaystyle{ m \left ( \gamma \right ) = m _{abs} \left ( \gamma \right ) / m_{abs} \left ( 90^o \right ) }[/math]

(2)

Nomenclature

Symbol	Description	Unit
ρH2O	density of water	kg / m^3
Cpair	heat capacity of air	J / kg / K
ρair	density of air	kg / m^3
precip. rate	precipitation rate	mm / hr
Tair	air temperature	deg C
Tsurface	surface temperature	deg C
RH	relative humidity (in [0,1])	-
p0	atmospheric pressure	mbar
z	reference height for uz	m
uz	wind velocity at reference height	m / s
z0	surface roughness length scale for wind	m
albedo	surface albedo in [0,1]	-
em_air	surface emissivity in [0,1]	-
dust atten. in [0, 0.3]	dust attenuation factor	-
cloud factor	cloud factor in [0,1], 0 for no clouds	-
canopy factor	forest canopy factor in [0,1], 0 for no canopy	-
slope	topographic slope in [0, infinity]	-
slope grid file	as flat binary, row-major file with 4-byte floats	-
aspect angle	aspect angle [radians] in [0,1]	-
aspect grid file	as flat binary, row-major file with 4-byte floats	-
time zone offset	offset, in hours, from Greenwich Mean Time (GMT), negative for east of prime meridian, positive otherwise	-
start month	start month for solar radiation calculations	-
start day	start day for solar radiation calculations	-
start hour	start hour for solar radiation calculations [decimal, 24-hour clock]	-
h	height above mean sea level	m
ρ	equals to ρ(h), air density at height h	kg / m3
ρ0	air density at h = 0	kg / m3
δ0	equals to n0 - 1	-
n0	refractive index for air at 0.7μm wavelength at h = 0	-
R	mean earth radius	m
m(γ)	the relative optical air mass at solar elevation γ	-
mabs(γ)	absolute optical air mass	-

Output

Symbol	Description	Unit
eair	vapor pressure of air	mbar
esurf	vapor pressure at the surface	mbar
QnSW	net shortwave radiation	W / m^2
QnLW	net longwave radiation, equals to LWin - LWout	W / m^2
emair	air emissivity in [0,1]	-

Notes

• Note on input parameters

For each input variable, you may choose from the droplist of data types. For the "Scalar" data type, enter a numeric value with the units indicated in the dialog. For the other data types, enter a filename. Values in files must also use the indicated units.

Single grids and grid sequences are assumed to be stored as RTG and RTS files, respectively. Time series are assumed to be stored as text files, with one value per line. For a time series or grid sequence, the time between values must coincide with the timestep provided.

For DEMs with pixel geometry and bounding box given in terms of Geographic coordinates, the latitude and longitude of each pixel is used in the calculations. For DEMs with a "fixed-length" pixel geometry (e.g. UTM coordinates), which tend to span smaller areas, the dialog prompts for a single lat/lon pair to be used in the calculations.

• Note on Equations

time zone:Boundaries of time zones can be very irregular and a time zone map should be consulted if you are unsure. The time zone is not simply a function of the longitude. You can select an adjacent time zone to include the effect of Daylight Savings Time. Time zones with non-integer offsets from GMT are not yet supported.

slope:Topographic slopes (not slope angles) are specified as dimensionless numbers [m/m]. A RiverTools grid (RTG file) with extension "_slope.rtg", "_mf-slope.rtg" or "_dinf-slope.rtg" can be used.

aspect:Aspect is specified as an angle measured in radians counter-clockwise from due east (the standard convention). A RiverTools grid (RTG file) with extension "_mf-angle.rtg" or "_dinf-angle.rtg" can be used for the (continuous-angle) aspect grid.

Q_SW is set to zero between the times of local sunset and local sunrise, so frames in the RTS file that correspond to nighttime hours will contain only zeros.

Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations:

• Upload file: http://csdms.colorado.edu/wiki/Special:Upload
• Create link to the file on your page: [[Image:<file name>]].

See also: Help:Images or Help:Movies

Developer(s)

Scott Peckham

References

Dingman, S.L (2002) Physical Hydrology, 2nd ed., Prentice Hall, New Jersey. (see Appendix E)

Kasten and Young (1989) Revised optical air mass tables and approximation formula. Applied Optics, 28 (22): 4735~4738. (for the optical air mass equation)

Liston, G. *******

Marks and Dozier (1992) ******* Water Resources Research.

Whitman, A.M. (2003) A simple expression for the equation of time, online document, http://www.sunspot.noao.edu/sunspot/pr/answerbook/expl-5.html

Links

• [Model:TopoFlow-Meteorology]
• [Model:TopoFlow]