Summary:

Overburden Pressure Compaction

The compaction rate due to overburden pressure, C_R2,i, is a linear function of the snow load pressure, P_s,i. The snow load pressure is calculated as the sum of the ice and liquid water contents of the layers above, plus half the ice and liquid water contents of the layer being compacted.

The viscosity coefficient, η, varies with snow density and temperature according to the equation:
η = f_1 f_2 η_0 (ρ_i/c_η) exp[a_η(T_f - T_i) + b_η ρ_i]

Where f_1 accounts for the presence of liquid water, and f_2 accounts for the presence of angular grains (though it is fixed to 4 since grain shape is not modeled).

The main points are:
1. Overburden pressure compaction rate is a linear function of snow load pressure.
2. Snow load pressure is calculated based on the ice and liquid water content of the snow layers.
3. Snow viscosity varies with density and temperature, accounting for liquid water and grain shape.