Environmental Effects on Radiation Fluxes during the Pre-Monsoon, 4,170-5,525 m, Annapurna Region, Nepal

Abstract

This paper addresses the net radiation balance as it is affected by high elevation, topography, and variable surface materials and surface conditions in the Annapurna region of central Nepal. Emphasis is given to shortwave radiation components. Heat flux data were collected during the pre-monsoon period at four sites north of Annapurna Himal at elevations of 4,170; 5,019; 5,200; and 5,526 m. Results from this and other investigations of radiation in the Himalaya confirm remarkably consistent high transmissiv- ities with low atmospheric turbidities. Seasonal cloudiness, elevation, and solar position appear to be the primary cause of changing global radiation in the region. Beam/diffuse ratios, in addition to expected cloud effects, are strongly influenced by slope, aspect, and surface material. For example, wall-originated diffuse radiation represented 15% of total global radiation at the 5,019 m Tilicho Lake site. Changes of local weather at Tilicho Lake, accompanied by snow flurries and subsequent snow melts, resulted in constantly changing albedos and highly variable longwave and net radiation values throughout most days.