Large discrepancy between observed and simulated precipitation trends in the ascending and descending branches of the tropical circulation

Abstract

Observed and model simulated changes in precipitation are examined using vertical motion at 500 hPa to define ascending and descending branches of the tropical circulation. Vertical motion fields from reanalyses were employed to subsample the observed precipitation data. An emerging signal of rising precipitation trends in the ascending regions and decreasing trends in the descending regimes are detected in the observational datasets. These trends are substantially larger in magnitude than present‐day model simulations and projections into the 21st century. The discrepancy cannot be explained by changes in the reanalysis fields used to subsample the observations but instead must relate to errors in the satellite data or in the model parametrizations. This has important implications for future predictions of climate change, the reliability of the observing system and the monitoring of the global water cycle.