Solar absorption by cirrus clouds and the maintenance of the tropical upper troposphere thermal structure

Radiative transfer calculations employing observed values of the ice crystal size distribution demonstrate that the absorption of solar radiation by cirrus clouds can make a significant contribution to the diabatic heating of the upper troposphere. The effects are investigated in a general circulation model (GCM) with interactive clouds; guided by observations, two experiments are performed assuming vastly different vertical profiles of the ice water density. Solar heating rates within the extensive cirrus decks associated with monsoon and other convective clouds reach values of 1.5 K day^-1. Thus, cirrus solar heating can be an important source for east-west asymmetries in the tropical diabatic heating. Cirrus solar absorption can also influence the meridional heating gradients within the upper troposphere. -from Authors