Convective Aggregation and the Amplification of Tropical Precipitation Extremes

Abstract:

It is widely believed that precipitation extremes will increase in response to a warming climate, as inferred from both observations and numerical simulations. In the absence of changes in atmospheric circulations, extreme precipitation is expected to increase in already-moist regions along a thermodynamical Clausius-Clapeyron scaling. However, within the tropics, the sensitivities inferred from observations are roughly twice as large, implying an unknown contribution from atmospheric dynamics. In this study, we investigate the relationship between convective aggregation and precipitation and the role that convective aggregation plays in amplifying the response of frequency of tropical precipitation extremes to interannual surface warming, using satellite observations and climate model simulations. We find that the occurrence of heavier precipitation coincides with a higher degree of convective aggregation. This relationship exhibits interannual variations. Both extreme precipitation events and convective aggregation tend to increase during warm, El Niño events compared to colder, La Niña events. In both the observation and models, increases in large-scale convective aggregation contribute to roughly one-third of the increase in extreme precipitation occurrence to interannual warming by shifting moderate-to-heavy precipitation events to more extreme precipitation intensities. The linkages between convective aggregation and precipitation extremes considered here offer insights into their potential response to anthropogenic warming.