Soil Heat Processes > Soil Heat Flow > Theory > Upper boundary condition
Soil surface temperature – snow covered soil

For periods with snow cover, soil surface temperature under the snow pack, Tss, is given by assuming steady state heat flow between the soil and a homogeneous snow pack, i.e. by setting the heat flow through the upper soil compartment equal to the heat flow in the snow pack (see figure below) and solving for Tss:

                                                               (1.4)

where the index 1 means the top soil layer, and the snow surface temperature is assumed to be equal to air temperature, Ta, or estimated from an energy balance approach for the snow surface (see switch “SnowSurfTemperature” in the section on snow. The weighting factor, a, is given by:

                                                            (1.5)

where ∆z denotes thickness, ksnow is the conductivity in the snow pack and kh is the conductivity in the uppermost soil compartment.

If the amount of liquid water in the snow pack, Swl, exceeds a threshold, swlmin, (fixed parameter value) soil surface temperature under the snow, Tss, is put equal to 0 oC.

 

Figure 1.1          The steady state assumption of heat flow through the upper soil layer and the snow pack

The heat flow in the snow pack is calculated as:

                                                          (1.6)

and in the uppermost soil compartment as:

                                                             (1.7)