The Influence of Microphysics on the Behavior of Moist Convection at Different Surface Temperatures

Abstract:

Simulations of radiative-convective equilibrium with a cloud-system resolving model are used to investigate the behavior of moist convection over a wide range of surface temperatures. We examine high percentiles of the simulated precipitation distribution (precipitation extremes). For surface temperatures above roughly 295 K, precipitation extremes increase with warming in proportion to the increase in surface moisture, following what is termed Clausius-Clapeyron (CC) scaling. At lower temperatures, however, the rate of increase of precipitation extremes with warming is sensitive to the choice of cloud and precipitation microphysics scheme used, and it differs markedly from CC scaling in some cases. Precipitation extremes are found to be sensitive to the fall speeds of hydrometeors, and this partly explains the different scaling results obtained with different microphysics schemes.

The choice of microphysics scheme also influences other aspects of the simulations, such as the top-of-atmosphere radiation budget, and these sensitivities are briefly discussed. The results highlight the challenges of representing sub-grid scale processes in climate models, even as increasing computational resources begin to allow climate simulations at near cloud-resolving resolution.