Changes of tropical precipitation and convective structure under global warming projected by CMIP5 model simulations

Regional changes of precipitation intensity, convective structure and column water vapor (CWV) in the Tropics are examined using climate model simulation outputs archived in the Coupled Model Intercomparison Project, phase 5 (CMIP5) for the representative concentration pathway 8.5 (RCP8.5) experiments. Under global warming, CWV increases homogeneously in space following the Clausius-Clapeyron scaling. In contrast, precipitation changes exhibit marked regional discrepancies with a mix of positive and negative anomalies in both mean ascending and descending regions. A moisture budget analysis indicates that changes of tropical precipitation are controlled mainly by the dynamic effect (-<omega'partial derivative(p)(q) over bar >), with a secondary contribution from the thermodynamics effect (-<(omega) over bar'&). Precipitation changes comply with the "wet-get-wetter" or "dry-get-drier" mechanism over the regions where dynamic and thermodynamic effects work together, accounting for about two thirds of the total tropical area. Examining changes of convection structure further show that regions with negative precipitation anomalies must be accompanied by the weakening of convection in the entire troposphere. Convection structure changes attributing to positive precipitation anomalies, nonetheless, appear to be very different depending on the regions. In the mean ascending region, the positive precipitation anomaly is associated with the deepening of convection. In the mean descending region, the positive precipitation anomaly is a result of proportionally enhanced convection within the troposphere. The above findings are based on area-mean results. Further details may emerge when viewing convection and precipitation changes at local scales.