A SATELLITE ANALYSIS OF DEEP CONVECTION, UPPER-TROPOSPHERIC HUMIDITY,AND THE GREENHOUSE-EFFECT

This paper combines satellite measurements of the upwelling 6.7-mu m r adiance from TOVS with cloud-property information from ISCCP and outgo ing longwave radiative fluxes from ERBE to analyze the climatological interactions between deep convection, upper-tropospheric humidity, and atmospheric greenhouse trapping. The satellite instruments provide un matched spatial and temporal coverage, enabling detailed examination o f regional, seasonal, and interannual variations between these quantit ies. The present analysis demonstrates that enhanced tropical convecti on is associated with increased upper-tropospheric relative humidity. The positive relationship between deep convection and upper-tropospher ic humidity is observed for both regional and temporal variations, and is also demonstrated to occur over a wide range of space and time sca les. Analysis of ERBE outgoing longwave radiation measurements indicat es that regions or periods of increased upper-tropospheric moisture ar e strongly correlated with an enhanced greenhouse trapping, although t he effects of lower-tropospheric moisture and temperature lapse rate a re also observed to be important. The combined results for the Tropics provide a picture consistent with a positive interrelationship betwee n deep convection, upper-tropospheric humidity, and the greenhouse eff ect. In extratropical regions, temporal variations in upper-tropospher ic humidity exhibit little relationship to variations in deep convecti on, suggesting the importance of other dynamical processes in determin ing changes in upper-tropospheric moisture for this region. Comparison of the observed relationships between convection, upper-tropospheric moisture,and greenhouse trapping with climate model simulations indica tes that the Geophysical Fluid Dynamics Laboratory (GFDL) GCM is quali tatively successful in capturing the observed relationship between the se quantities. This evidence supports the ability of the GFDL GCM to p redict upper-tropospheric water vapor feedback, despite the model's re latively simplified treatment of moist convective processes.