| OCR Text |
Show is the latent heat flux released at the surface by condensation ( sublimation). Here E is the vapor pressure at the surface, e, the vapor pressure at each height of the same corresponding heat exchange coefficient as for rj- , p is the air pressure and cp the specific heat at constant pressure. The value of r is taken as the heat of vaporization of ice, r- » for the phase change ice tzj. vapor, and that of water, r^ , for the change water ^ vapor. These, together with the heat of fusion of ice, rs , are related by rg = rw + rs ( 4) All the heat fluxes in Equation ( 1), which can for example be expressed in meal cm~ 2 min~ l, are counted as positive when they contribute heat to the surface. It thus follows in particular that for evaporation V< 0, and for melting S< 0. In a similar manner for the mass balance, a positive sign is given to the ice accumulation per unit time, M, calculated in terms of an equivalent layer thickness of water which can be assigned the units of mm h--*-. The manifold possibilities of phase changes make it necessary to limit the validity of M to the processes at the surface and its immediate vicinity. Phase changes in deeper layers, such as those accompanying the refreezing of percolating surface meltwater, are not included in M. The released heat which reaches the surface in this case is included in B. As noted above, S encompases only the heat involved in the phase change ice ^ water at the surface or immediately beneath the thin surface water film. |
