Snow Model

A three-layer snow model is used for snowcover on soil, icesheet and sea-ice surfaces, including fractional areal cover when the snow is thin. The snow column at each grid point is modeled by standard vertical finite-difference techniques. Heat is diffused linearly through the snow, and the total thickness changes due to melting or snowfall on the upper layer. Fractional snow cover is accounted for by imposing a minimum snow thickness of 15 cm and adjusting the fractional area to conserve snow mass. Snow moisture content, percolation and refreezing of melted snow are all included along the lines of Loth et.al. (1993). This particularly helps

1. the prediction of ice-sheet budgets where refreezing is an important process near the margins (e.g. Paterson, 1969; Ambach, 1985), and
2. the unrealistic loss of snowmelt to runoff while the soil is still frozen (which led to unrealistically dry soils in the northern boreal forests in GENESIS version 1.02).

12/8/97