energy_bal_func

Author:

Keith Cherkauer

Date:

January 3, 1996

Description:

This subroutine solves the surface energy balance in order to find the surface temperature.

References

Liang, Xu, E. F. Wood, and D. P. Lettenmaier, Modeling Ground Heat Flux in Land Parameterization Schemes, submitted JGR 1997.

Cherkauer, K, and D. P. Lettenmaier, Modeling the Affects of Frozen Soils in the GCIP LSA-NC, GCIP PRA/PI meeting, Boulder, CO, Nov 1997.

Input Variables:

Variable	Type	Units	Description
Ts	double	C	Surface Temperature
T2	double	C	Temperature at bottom of soil column
Ts_old	double	C	Previous surface temperature
T1_old	double	C	Previous temperature at boundary between top two layers
Tair	double	C	Air temperature
ra	double	s/m	Aerodynamic resistance
atmos_density	double	kg/m^3	Denisty of the atmosphere
shortwave	double	W/m^2	Net shortwave radiation
longwave	double	W/m^2	Incoming longwave radiation
albedo	double	fraction	Surface albedo
emissivity	double	fraction	Surface emissivity
kappa1	double	W/m/K	Thermal conductivity of top layer
kappa2	double	W/m/K	Thermal conductivity of second layer
Cs1	double	J/m^3/K	Volumetric heat capacity of top layer
Cs2	double	J/m^3/K	Volumetric heat capacity of second layer
D1	double	m	Thickness of top layer
D2	double	m	Thickness of second layer
dp	double	m	Depth of soil column
delta_t	double	s	Time step
Le	double	ENTER_UNITS	Latent heat of vaporization
Evap	double	mm	Evaporation
moist	double	mm/mm	Moisture content of top layer
ice0	double	mm/mm	Previous ice content of top layer
max_moist	double	mm/mm	Maximum moisture content of top layer
bubble	double	cm	Bubbling pressure of soil column
expt	double	N/A	Soil moisture exponential
surf_atten	double	fraction	Surface attenuation caused by vegetation (if present)

Output Variables:

Variable	Type	Units	Description
error	double	W/m^2	Surface energy balance error
grnd_flux	double *	W/m^2	Ground heat flux
T1	double *	C	Soil temperature between first and second layers
latent_heat	double *	W/m^2	Latent heat flux
sensible_heat	double *	W/m^2	Sensible heat flux

Subroutines Called:

maximum_unfrozen_water

Modifications and Limitations

Ground heat flux equations modified to account for latent heat needed to freeze and thaw the soil (Cherkauer, 1997). When soil is unfrozen, or if frozen soil option not selected, equation reverts back to it's original form.

Surface attenuation parameter added along with other vegetation routines.

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