OCR Text |
Show R 102 101 1 10" 1 10- 2 10- 3 cm XL 12 36 115 352 1150 3620 meal cm~ 2 min-* grd" » The values given here for moderately curved surfaces are close to those for a plane surface, while at the ridges values occur which are many times greater. The following discussion will be concerned primarily with forms whose heat exchange coefficient < T. exceeds 50 meal cm"' min" 1 deg" 1, such as ridges whose width ( 2R) is 10 cm or less. The first step is to investigate under which meteorological conditions the ablation - M increases or decreases. The increase of - M with CC. means that ridges will be ablated away more rapidly than less curved parts of the surface. In these cases existing surface irregularities will be smoothed out. On the other hand, when ablation - M decreases with increasing CC. , the ridges will experience less ablation than other parts such that in the course of time pre- existing irregularities will be continually intensified. These snow cover ablation forms, whose best- known example is penitent snow, can occur only in a relatively narrow domain of meteorological parameters. The following discussion will serve to delineate the boundaries of this domain. Because the ablation, - M, depends on air pressure, p, as well as on air temperature i)\ , the vapor pressure eL , the heat input Q+ B and-- what is especially important here- on the heat transfer coefficient, iZ" L , it is not possible to depict the effects of all these parameters in a single illustration. Instead an attempt will be made to define the domain of values leading to ablation which accentuates irregularities, and then by means of some examples display - M as a function of CCL for pre- assigned values of p, i/ j, eL , and Q+ B. 17 |