LONGWAVE RADIATION IN THE HIMALAYAS OF CENTRAL NEPAL AND NORTHWEST INDIA

Abstract

Short-term climatic field data taken in high elevations of Nepal and Kashmir-Ladakh, India, are used to evaluate incoming, outgoing, and net longwave radiation changes with elevation. Sky brightness temperatures were monitored and converted to equivalent IR, full hemisphere sky emittance values. Surface temperatures were also recorded. Calculated sky radiant IR fluxes are compared to several models of longwave incoming radiation. The model of Brutsaert compares favorably with instrument-derived longwave incoming radiation values in comparison to other empirical equations tested.

Elevational gradients of longwave incoming radiation were found to range from -34 W/m² per km (Kashmir-Ladakh) to -49 W/m² per km (India-Nepal) and are consistent, in a regional climate context, with the few available analyses of longwave components for some other mountain locales at similar latitudes. Net longwave radiation becomes increasingly more negative at high elevations and patterns of net longwave radiation are strongly controlled by the complex mosaic of surface types in mountainous terrain. [Key words: Himalayas, Nepal, India, net longwave radiation, elevation gradients.]