It has been known that the upper troposphere is moistened by deep convection, however, consequences of the deep convection over the entire tropics is the question at issue. Using both infrared and microwave water vapor radiances, we examined the moistening processes in the upper troposphere over the Tropical Indian Ocean during a winter season, in which deep convection prevails over the equatorial Indian Ocean. It is observed that the dry subtropical area becomes drier while humidity becomes higher in the cloudy region with increased convection size. It is also noted that moistening processes from semitransparent thin cirrus appears to mediate dryness over the whole.

Now it is a natural question whether these features can be simulated by the general circulation model, thus we use NCAR CCM3 for examining moistening processes in the upper troposphere in the model atmosphere. Results indicated that CCM3 also shows humidity increase with increased size of deep convective cloud clusters, but the model depicts different moistening/drying physics in particular outside deep convective cloud clusters.