Surface forcing of the infrared cooling profile over the Tibetan Plateau. Part I: influence of relative longwave radiative heating at high altitude

Abstract

The role of the Tibetan Plateau on the behaviour of the surface longwave radiation budget is examined, and the behaviour of the vertical profile of longwave cooling over the plateau, including its diurnal variation, is quantified. The investigation has been conducted with the aid of datasets obtained during the 1986 Tibetan Plateau Meteorological Experiment (TIPMEX-86). A medium spectral-resolution infrared radiative transfer model using a simple modification for applications in idealized complex (valley) terrain is developed for the study. Atmospheric longwave cooling is significantly influenced by variations in the biophysical composition of the surface and the associated thermal diurnal cycle. It is estimated that natural variations of surface emissivity could modulate longwave cooling by up to 40%. The largest impact would occur at a time when the surface temperature is high and the relative longwave radiative heating of the lower atmosphere by the surface reaches its maximum value. -from Authors