Analysis of upper-tropospheric humidity in tropical descent regions using observed and modelled radiances

Abstract. We use multiple observations and climate model simulations to study upper tropospheric humidity (UTH) in tropical descent regions. A satellite simulator is used to generate UTH from model fields to ensure a like-to-like comparison. We have shown that HadGEM2 is generally able to reproduce the patterns and magnitude of UTH in these regions. In both models and observations, the major mode of UTH variability in these regions is associated with El Nino and Southern Oscillation (ENSO); a negative UTH anomaly is seen during El Nino years. There is no significant trend in UTH in these regions, where even a small negative trend would lead to an important reduction of the positive water vapour feedback on global warming.