Effect of Lofted Ice Sublimation from Tropical Deep Convection on TTL Water Vapor

We investigate the role of sublimation of convectively lofted ice on water vapor budget in tropical tropopause layer (TTL) using satellite observations, reanalyses, a trajectory model, and a global climate model. It has previously been shown that tropical averaged TTL water varies with the tropical tropospheric temperature (∆T). In this analysis, we examine the cause of this by examining the spatial distribution of the impact of ∆T on TTL water vapor. We find that, as the troposphere warms, TTL water vapor increases in the Tropical Warm Pool and Indian Ocean, while decreasing in Central Equatorial Pacific (CEP). Analysis of models shows that this is due to the zonal shift of coldest TTL temperature during ENSO events. However, the decrease in the observations is not as pronounced as would be expected if TTL water were only regulated by water vapor. We hypothesize that this difference is due to the sublimation of convectively lofted ice. The observed deep convection clouds observed by satellites support the role of sublimation of cloud ice on TTL water vapor, as does a parallel analysis using GEOSCCM output and trajectory model driven by GEOSCCM meteorology. We conclude that evaporation of convectively lofted ice plays a role in setting the distribution of TTL water vapor.