Model:TopoFlow-Snowmelt-Energy Balance: Difference between revisions
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{{Input - Output description | {{Input - Output description | ||
|Describe input parameters=The input variables for the Energy Balance method of estimating runoff due to snowmelt are defined as follows: | |||
Q_SW = net shortwave radiation (W / m^2) | |||
Q_LW = net longwave radiation (W / m^2) | |||
T_air = air temperature (deg C) | |||
T_surf = surface (snow) temperature (deg C) | |||
RH = relative humidity (none) (in (0,1)) | |||
p_0 = atmospheric pressure (mbar) | |||
u_z = wind velocity at height z (m / s) | |||
z = reference height for wind (m) | |||
z0_air = surface roughness height (m) | |||
h0_snow = initial snow depth (m) | |||
h0_swe = initial depth, snow water equivalent (m) | |||
ρ_snow = density of the snow (kg / m^3) | |||
c_snow = specific heat capacity of snow (J / (kg deg_C)) | |||
ρ_air = density of the air (kg / m^3) | |||
c_air = specific heat capacity of air (J / (kg deg_C)) | |||
L_f = latent heat of fusion, water (J / kg) (334000) | |||
L_v = latent heat of vaporization, water (J / kg) (2500000) | |||
e_air = air vapor pressure at height z (mbar) | |||
e_surf = vapor pressure at the surface (mbar) | |||
g = gravitational constant = 9.81 (m / s^2) | |||
κ = von Karman's constant = 0.41 (unitless) | |||
The behavior of this component is controlled with a configuration (CFG) file, which may point to other files that contain input data. Here is a sample configuration (CFG) file for this component: | |||
Method code: 2 | |||
Method name: Energy_Balance | |||
Time step: Scalar 3600.00000000 (sec) | |||
Cp_snow: Scalar 2090.00000000 (J/kg/K) | |||
rho_snow: Scalar 300.00000000 (kg/m^3) | |||
c0: Scalar 2.70000005 (mm/day/deg C) | |||
T0: Scalar -0.20000000 (deg C) | |||
h0_snow: Scalar 0.50000000 (m) | |||
h0_swe: Scalar 0.15000000 (m) | |||
Save grid timestep: Scalar 60.00000000 (sec) | |||
Save mr grids: 0 Case5_2D-SMrate.rts (m/s) | |||
Save hs grids: 0 Case5_2D-hsnow.rts (m) | |||
Save sw grids: 0 Case5_2D-hswe.rts (m) | |||
Save cc grids: 0 Case5_2D-Ecc.rts (J/m^2) | |||
Save pixels timestep: Scalar 60.00000000 (sec) | |||
Save mr pixels: 0 Case5_0D-SMrate.txt (m/s) | |||
Save hs pixels: 0 Case5_0D-hsnow.txt (m) | |||
Save sw pixels: 0 Case5_0D-hswe.txt (m) | |||
Save cc pixels: 0 Case5_0D-Ecc.txt (J/m^2) | |||
|Input format=ASCII, Binary | |Input format=ASCII, Binary | ||
|Output format=ASCII, Binary | |Output format=ASCII, Binary | ||
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{{Process description model | {{Process description model | ||
|Describe processes represented by the model=The Energy Balance method for modeling snowmelt. | |||
|Describe key physical parameters and equations=Equations Used by the Energy-Balance Method | |||
M = (1000 * Q_m) / (ρ_water * L_f) = meltrate (mm / sec) | |||
M_max = (1000 * h_snow / dt) * (ρ_water / ρ_snow) = max possible meltrate (mm / sec) | |||
dh_snow = M * (ρ_water / ρ_snow) * dt = change in snow depth (m) | |||
Q_m = Q_SW + Q_LW + Q_h + Q_e - Q_cc = energy flux used to melt snow (W / m^2) | |||
Q_h = ρ_air * c_air * D_h * (T_air - T_surf) = sensible heat flux (W / m^2) | |||
Q_e = ρ_air * L_v * D_e * (0.662 / p_0) * (e_air - e_surf) = latent heat flux (W / m^2) | |||
D_n = κ^2 * u_z / LN((z - h_snow) / z0_air)^2 = bulk exchange coefficient (neutrally stable conditions) (m / s) | |||
D_h = D_n / (1 + (10 * Ri)), (T_air > T_surf) = bulk exchange coefficient for heat (m / s) (stable) | |||
= D_n * (1 - (10 * Ri)), (Tair < Tsurf) = bulk exchange coefficient for heat (m / s) (unstable) | |||
D_e = D_h = bulk exchange coefficient for vapor (m / s) | |||
Ri = g * z * (T_air - T_surf) / (u_z^2 (T_air + 273.15)) = Richardson's number (unitless) | |||
Q_cc = (see note below) = cold content flux (W / m^2) | |||
E_cc(0) = h0_snow * ρ_snow * c_snow * (T_0 - T_snow) = initial cold content (J / m^2) (T0 = 0 now) | |||
e_air = e_sat(T_air) * RH = vapor pressure of air (mbar) | |||
e_surf = e_sat(T_surf) = vapor pressure at surface (mbar) | |||
e_sat = 6.11 * exp((17.3 * T) / (T + 237.3)) = saturation vapor pressure (mbar, not KPa), Brutsaert (1975) | |||
|Describe length scale and resolution constraints=Recommended grid cell size is around 100 meters, but can be parameterized to run with a wide range of grid cell sizes. DEM grid dimensions are typically less than 1000 columns by 1000 rows. | |Describe length scale and resolution constraints=Recommended grid cell size is around 100 meters, but can be parameterized to run with a wide range of grid cell sizes. DEM grid dimensions are typically less than 1000 columns by 1000 rows. | ||
|Describe time scale and resolution constraints=The basic stability condition is: dt < (dx / u_min), where dt is the timestep, dx is the grid cell size and u_min is the smallest velocity in the grid. This ensures that flow cannot cross a grid cell in less than one time step. Typical timesteps are on the order of seconds to minutes. Model can be run for a full year or longer, if necessary. | |Describe time scale and resolution constraints=The basic stability condition is: dt < (dx / u_min), where dt is the timestep, dx is the grid cell size and u_min is the smallest velocity in the grid. This ensures that flow cannot cross a grid cell in less than one time step. Typical timesteps are on the order of seconds to minutes. Model can be run for a full year or longer, if necessary. |
Revision as of 18:11, 17 February 2010
Contact
Name | Scott Peckham |
Type of contact | Model developer |
Institute / Organization | CSDMS, INSTAAR, University of Colorado |
Postal address 1 | 1560 30th street |
Postal address 2 | |
Town / City | Boulder |
Postal code | 80305 |
State | Colorado |
Country | USA"USA" is not in the list (Afghanistan, Albania, Algeria, Andorra, Angola, Antigua and Barbuda, Argentina, Armenia, Australia, Austria, ...) of allowed values for the "Country" property. |
Email address | Scott.Peckham@colorado.edu |
Phone | 303-492-6752 |
Fax |
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