Radiation balance of the tropical transition region

Abstract

Aerosols and trace gases are transported effectivly within the tropical troposphere by deep convection. The tropical convection reaches the stratosphere only in rare cases. In fact most of it ends distinctly below the stratosphere. Nevertheless the major part of mass exchange between troposphere and stratosphere takes place in the tropics. Hence processes, which influence the disposition of air in the tropical transition layer (TTL), are of crucial importance for exchange between troposphere and stratosphere. Radiative heating can enable a further ascend of air into the stratosphere. Thus the level Q=0, where the radiation budget is balanced, is a borderline for tropospheric/stratospheric exchange. Both the solar and the thermal radiation budget determine the heating rate in the TTL. In the clear sky case the heating rate is effected by absorption and emission of radiation mainly by water vapour, CO₂, and O₃. For cloudy sky also thermal heating of the cloud base, thermal cooling of the cloud top of optically thick clouds or thermal heating of thin cirrus clouds, as well as solar heating of the cloud top are of particular interest.