| OCR Text |
Show is exceeded. At lower air temperatures, ablation always promotes irregularities at a melting surface, so that unevenness of the surface is increasingly accentuated. Ablation at a ridge first becomes uniform when the ridge becomes so sharp that the melting surface is changed to a non- melting one. This cross- over from melting to non- melting surfaces corresponds, as already mentioned, to the inflection point on the curves of Figs. 7a through 7c. As shown by the following equation derived from Equation ( 8) as well as ( 21) Q + B XL = pcp < X^ is the greater ( the ridges as shown in Equation ( 19) are the sharper), the higher are the air temperature rCr and the vapor pressure e. . More precisely, OC. is the greater the less the equivalent air temperature determined with rw differs from that for saturated air at 0° C. In this connection the equivalent air temperature determined with r., cannot, however, exceed that for saturated air at 0° C, for otherwise ablation could not accentuate surface irregularities. Furthermore, this accentuating effect of ablation is slight, as shown by Curve No. 7 in Fig. 7c, when the departure from the latter equivalent temperature ( determined with rw ) is small. Independently of this somewhat contradictory influence of - V7 and e, , ( X, is the greater, the greater is Q+ B. In this case the internal heat flux B plays only a subordinate part, and especially so at the ridges. Furthermore, it can be assumed that the terrestrial radiation balance of around - 100 meal cm min" does not materially change. This is especially true in comparison with the other part, Q, of the radiation balance, namely the solar 26 |
