Tropical Precipitation Extremes and Their Modulation by Convective Organization in RCEMIP

We examine extreme tropical precipitation events using model simulation data from the Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP). We consider simulations at three different sea surface temperatures (SSTs) and two domain configurations; a small domain that prohibits convective organization and a large domain that allows it. This permits examination of how the presence of convective organization influences extreme precipitation, defined as a high percentile of hourly precipitation, and its response to SST warming. At a given SST, simulations with convective organization have more intense precipitation extremes than those without it. In the model average, we find that both with and without convective organization, extreme precipitation rates rise with SST approximately following Clausius-Clapeyron. Models with explicit convection exhibit much better agreement than those with parameterized convection, demonstrating the importance of resolving convection for examining tropical precipitation extremes. Among models with explicit convection, those which show increased organization with warming show more rapid increases in precipitation with warming.

We also apply the precipitation extremes scaling given by O’Gorman and Schneider (2009) to examine changes in the extreme condensation events leading to extreme precipitation. Even on hourly timescales at individual grid points, we find correlations between increases in this scaling and increases in extreme rainfall, though the scaling grows more slowly than the Clausius-Clapeyron relation. Increased organization correlates with the dynamic and implied efficiency contributions to changes in precipitation extremes in CRMs, a relationship which appears to be modulated by environmental moisture in the aggregated region. This work demonstrates the value of a controlled intercomparison of both models with explicit and parameterized convection for studying the influence of convective organization on precipitation extremes.