OCR Text |
Show mentioned, CC. occurs in them only indirectly in the expressions - M/ GC. and ( QfB)/ fl\ . This question will be examined later in detail. Certain points will next be discussed which concern ablation in general as well as a smooth surface. 6. Ablation by Evaporation and by Melt As already noted several times, the change in amount of ice M can take place by two processes: 1. Evaporation of ice or its sublimation from water vapor ( My ) 2. Melting of ice or the freezing of water ( Ms ) The domain of a non- melting snow surface belongs to 1., that for a melting surface to 2. There could be uncertainty about how to assign the small sector Condensation and Freezing, for here water is deposited from the air and then part of this is changed to ice. Because the surface is wet, sublimation does not occur and one can classify this case as a melting surface with a negative sign for M. The values of M can be obtained from Fig. 2 for p = 760 torr and from Fig. 3 for p = 525 torr. In this case Mv is zero in the domain of melt and Me is zero in the non- melting domain. While there is no upper limit to - Ms , ablation by evaporation, Mv , reaches its maximum value when completely dry air occurs over the melting snow surface. For p = 760 torr, the value found in Fig. 2 is - M/< tL = 0.0094 mm h~ Vmcal cm~^ min" 1 deg" 1. For < XL = 10 meal cm" 2 min" 1 deg" 1, the maximum ablation by evaporation would be 0.094 mm h" 1 or 2.25 mm d" . For the corresponding value of p = 525 torr in Fig. 3, these values for the same d. are 0.136 mm h" 1 or 3.26 mm d" . 12 |