Surface forcing of the infrared cooling profile over the Tibetan Plateau. Part II: cooling-rate variation over large-scale plateau domain during summer monsoon transition

Abstract

The spatial distribution of longwave cooling over the plateau is significantly influenced by variations in biophysical composition, topography, and elevation, the surface thermal diurnal cycle, and various climatological factors. An important factor is soil moisture. Bulk clear-sky longwave cooling rates are larger in the southeast sector of the plateau than in the north. This is because rainfall is greatest in the southeast, whereas the north is highly desertified and relative longwave radiative heating by the surface is greatest. Another important phenomenon is that the locale of a large-scale east-west-aligned spatial gradient in radiative cooling propagates northward with time. During the premonsoon period (May-June), the location of the strong spatial gradient is found in the southeastern region of the plateau. An overall decrease in longwave cooling takes place in the lower atmosphere immediately prior to the arrival of the active monsoon. -from Authors