How Do the Tropics Precipitate? Daily Variations in Precipitation and Cloud Distribution

Abstract

What controls the variability of daily precipitation averaged over the tropics? Are these the most numerous precipitation rates or the most intense ones? And do they relate to a specific cloud type? This work addresses these questions using precipitation from the one-year simulation of the global-coupled storm-resolving ICOsahedral Non-hydrostatic model run in its Sapphire configuration (ICON-Sapphire) and observations. Moreover, we develop a framework to analyze the precipitation variability based on the area covered by and the mean intensity of different groups of precipitation rates. Our framework shows that 60 % of the precipitation variability is explained by precipitation rates between 20 mm d⁻¹ and 70 mm d⁻¹, but those precipitation rates only explain 46 % of the mean precipitation in the tropics. The decomposition of the precipitation variability into the area fraction and mean intensity of a set of precipitation rates shows that this variability is explained by changes in the area fraction covered by precipitation rates between 20 mm d⁻¹ and 70 mm d⁻¹, not by changes in the mean intensity. These changes in the area fraction result from changes in the area covered by congestus clouds, not by cumulonimbus or shallow clouds, even though congesti and cumulonimbi contribute equally to the mean tropical precipitation.

Overall, ICON-Sapphire reproduces the probability density function of precipitation rates and the control of specific precipitation rates on the tropical mean precipitation and variability compared to observations.