Environmental controls on tropical mesoscale convective system precipitation intensity

Abstract

Using multiple independent satellite and reanalysis datasets, we compare relationships between mesoscale convective system (MCS) precipitation intensity (Pmax), environmental moisture, large-scale vertical velocity, and system radius among tropical continental and oceanic regions. A sharp, nonlinear relationship between column water vapor (CWV) and Pmax emerges, consistent with nonlinear increases in estimated plume buoyancy. MCS Pmax increases sharply with increasing boundary layer and lower free tropospheric (LFT) moisture, with the highest Pmax values originating from MCS environments exhibiting a peak in LFT moisture near 750 mb. MCS Pmax exhibits strikingly similar behavior as a function of water vapor among tropical land and ocean regions. Yet while the moisture-Pmax relationship depends strongly on mean tropospheric temperature, it does not depend on sea surface temperature (SST) over ocean or surface air temperature (SAT) over land. Other Pmax dependent factors include system radius, the number of convective cores, and the large-scale vertical velocity. Larger systems typically contain wider convective cores and higher Pmax, consistent with increased protection from dilution due to dry air entrainment and reduced re-evaporation of precipitation. Additionally, stronger large-scale ascent generally supports greater precipitation production. Lastly, temporal lead-lag analysis suggests that anomalous moisture in the lower-middle troposphere favors convective organization over most regions. Overall, these statistics provide a physical basis for understanding environmental factors controlling heavy precipitation events, providing metrics for model diagnosis and guiding physical intuition regarding expected changes to precipitation extremes with anthropogenic warming.