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, eair, and net shortwave (solar) radiation, QnSW, 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, Tair, 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.
Model parameters
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
| 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.
QSW 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)
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) Climate and Energy exchange at the Snow Surface in the Alpine Region of the Sierra Nevada 1. Meteorological Measurements and Monitoring. Water Resources Research, 28(11), 3029~3042.
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
