Increased Frequency of Extreme Tropical Deep Convection: AIRS Observations and Climate Model Predictions

Abstract

Atmospheric Infrared Sounder (AIRS) data from the tropical oceans (30 degrees N to 30 degrees S) are used to derive the probability of the process resulting in deep convective clouds (DCCs) as function of the sea surface temperature (SST). For DCC at or below the tropopause the onset temperature of this process shifts at the same rate as the increase in the mean SST. For tropopause overshooting DCC, which are associated with extreme rain events, the shift of the onset temperature is slower, causing their frequency to increase by about 21%/K of warming of the oceans. This sensitivity is not inconsistent with the sensitivity of the increase of extreme deep convective rain in the National Center for Atmospheric Research Community Atmosphere Model version 5 model for a warmer SST. The mean of the 36 fifth Phase of the Coupled Model Intercomparison Project models predicts a 2.7 K warmer tropical SST by the end of this century, resulting in a 60% increases in the frequency of tropopause overshooting DCC. Plain Language Summary We use 15 years of Atmospheric Infrared Sounder observations of the tropical oceans to derive the probability of the deep convective cloud (DCC) process as a function of the sea surface temperature. Based on this, the frequency of extreme (tropopause overshooting) DCCs will increase about 21% per 1 K of warming of the tropical oceans. Tropopause overshooting DCC are correlated with extreme rain rates. We evaluated the expected increase in the frequency of extreme precipitation in the National Center for Atmospheric Research Community Atmosphere Model version 5 model in a warmer tropical ocean. The increase of extreme rain rates in the model is consistent with the Atmospheric Infrared Sounder-derived increase in frequency of extreme DCC. The mean of the fifth Phase of the Coupled Model Intercomparison Project models predicts a 2.7 K increase in the surface temperature of the tropical oceans by the end of this century. This means that the frequency of extreme DCC in the tropical oceans could increase by about 60%.