Surface energy balance of snow
The snow surface temperature can be assumed to be equal to the air temperature or it can be estimated by solving the energy balance equation of the snow surface (see switch SnowSurfTemperature):
where Rn,snow, is the available net radiation at the snow surface, Hsnow and LEsnow are the sensible and latent heat fluxes from the snow surface to the atmosphere and qh,snow is the snow surface heat flux. The heat fluxes in Eq. (4.63) are estimated by an iterative procedure where the snow surface temperature is varied according to a given scheme:
1. The turbulent fluxes of latent and sensible heat are calculated with the same methods as described in the surface energy balance approach for the soil evaporation (Eq. (4.1)-(4.5) and Eq. (4.12)- (4.25)) (see switch StabilityCorrection).
2. A steady state solution is assumed for the heat flux through the snow pack and to the middle of the uppermost soil layer (Eq. 1.4 in “Soil Heat Processes”), implying new heat storage in the snow pack. The influence of water vapour flow on the heat flux through the snow and the soil surface may be included according to Eq. (4.5)-(4.6) (see switch “SoilVapour” in “General Options”).
3. If the estimated snow surface temperature, Tsnows, is above 0°C it is set to 0°C and the surface fluxes are recalculated. The remaining residual of net radiation, latent heat flux and sensible heat flux is considered as part of the snow surface heat flux, and may thus contribute to snow melt if the heat balance approach for snow melt is used.