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The larger degree-day factors for snow and ice ablation in the Nepalese glaciers than in most of the alpine glaciers in Europe (Table 4 in Braithwaite and Zhang 2000) are mainly due to ablation attributed to absorbed global radiation at the high altitude where the PDD is low because of low summer air temperature. For example, considerable amount of net shortwave radiation, the main energy source for ablation in the Himalayas, was found even at and around 0◦ C air temperature on Glacier AX010 (Kayastha et al.

5 correspond to this z0 value. The transfer mechanisms of momentum and of other scalar admixtures are different at the surface, and consequently the roughness lengths have different values for momentum, water vapour and heat, which were calculated following Andreas (1987). 5 MODELLING THE SURFACE MICROTOPOGRAPHY To assess the effect of the surface ablation morphology on the interception of solar radiation and on the longwave radiative budget, a high-resolution digital elevation model of the surface with 1 cm grid cell spacing was created, and the solar radiative and long-wave models applied to it.

They are computed in a slightly modified way from Greuell et al. (1997) as explained by Corripio (2004), with terrain and solar parameters such as vector normal to the surface, shading, horizon configuration and solar vector calculated after Corripio (2003b). 5, where the differences between modelled and measured data were smaller than the nominal pyranometer accuracy (10%). In this case, the valley is uniformly covered in snow and runs east to west, for different configurations there is a small error introduced by the necessary simplification and symmetry assumption of the terrain configuration parameters.