NOTES AND CORRESPONDENCE Moistening Processes in the Upper Troposphere by Deep Convection: A Case Study over the Tropical Indian Ocean

Abstract

Moistening processes in the upper troposphere are examined by relating upper tropospheric humidity (UTH) estimates from SSM/T-2 and Meteosat measurements to convective clouds over the Indian Ocean. Results are compared against NCAR/CCM3 outputs. The analysis separating the tropics into four cloud areas, i.e., deep convective, middle cloud, thin cirrus, and clear/low cloud area, indicates that the upper troposphere above the clear/low cloud area becomes drier (moister) in response to increases (decreases) in convective activity in the tropics. On the other hand, the area between deep convective cloud clusters, and clear/low cloud area, also appears to be moistened by thin cirrus originating from deep convective clouds. Although the CCM3 model reproduces the average number of cloud clusters found in the satellite observations, the model-derived UTH shows significantly different features, i.e., a drier upper troposphere within deep convective clusters, a much higher UTH over the clear/low cloud area, and a slight increase of UTH over the clear/low cloud area with respect to increases in the deep convective area, suggesting that the model needs more accurate physics for better description of the moistening/drying processes.