On Snow Cover Ablation

On_Snow_Cover_Ablation - Page 2

The two processes of evaporation and melting can cause the ablation of a snow or ice layer. From the standpoint of energy transfer in this process, melting is much more efficient, for it requires 80 cal g~ l while evaporation requires 677 cal g~ l. At air temperatures below 0° C ablation by evaporation predominates, as noted by R. Geiger Qfj, while at higher temperatures melting predominates. The following discussion will elucidate the various possible combinations of these processes. H. G. Mllller [ 4] has discussed these for the special case where the surface receives no heat from radiation or from conduction from below. This limitation will now be set aside. 1. The Heat and Mass Economy The heat balance equation for the surface is written Q+-( B + S) + L+ V = 0. ( 1) where Q is the radiation balance at the surface. B+ S encompasses all the heat fluxes from the space beneath the surface, where - S signifies the heat used for surface melting and B the remainder. L = - aL(& - & L) ( 2) is the sensible heat flux from the air, where .^- is the surface temperature and .£-. is the air temperature at the height where the heat transfer coefficient is 0CL . pcp