ENVIRONMENTAL-EFFECTS ON RADIATION FLUXES DURING THE PREMONSOON, 4,170-5,525 M, ANNAPURNA REGION, NEPAL

This paper addresses the net radiation balance as it is affected by hi gh elevation, topography, and variable surface materials and surface c onditions in the Annapurna region of central Nepal. Emphasis is given to shortwave radiation components. Heat flux data were collected durin g the pre-monsoon period at four sites north of Annapurna Himal at ele vations of 4,170; 5,019; 5,200; and 5,526 m. Results from this and oth er investigations of radiation in the Himalaya confirm remarkably cons istent high transmissivities with low atmospheric turbidities. Seasona l cloudiness, elevation, and solar position appear to be the primary c ause of changing global radiation in the region. Beam/diffuse ratios, in addition to expected cloud effects, are strongly influenced by slop e, aspect, and surface material. For example, wall-originated diffuse radiation represented 15% of total global radiation at the 5,019 m Til icho Lake site. Changes of local weather at Tilicho Lake, accompanied by snow flurries and subsequent snow melts, resulted in constantly cha nging albedos and highly variable longwave and net radiation values th roughout most days.