Seasonal variations of upper tropospheric water vapor and high clouds observed from satellites

Multiyear satellite measurements of specific humidity at 215 mbar from the Microwave Limb Sounder aboard the Upper Atmosphere Research Satellite and cloud amount from the International Satellite Cloud Climatology Project have been used to investigate seasonal variations of upper tropospheric water vapor (UTWV), high clouds, and deep convection. The tropical and extratropical UTWV for each hemisphere have maximum values in summer and minimum values in winter because of the moistening effect of the tropical deep convection. The seasonal change of high cloud amount is similar to UTWV in the tropics but very different in the extratropics. Implications of the present results for the water vapor feedback in the climate system are discussed.