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.

The Behaviors of Intraseasonal Cloud Organization During DYNAMO/AMIE

“…The quantity peaks slightly before and within MJO enhanced phase at the time when the domain‐averaged rainfall peaks (Figure 4a) and the rain clusters had their highest number density and size (Figures 5a and 6b). This result is consistent with the well‐known relationship between column relative humidity and precipitation within the tropics (e.g., Ahmed & Schumacher, 2015; Bretherton et al., 2004; Louf et al., 2019; Schiro et al., 2020). However, the vertical shear in all layers peaks during the decaying phase of the MJO when $${I}_{\text{org}}^{\ast }$$ maximizes (Figures 9e and 9f).…”

Distinguishing Convective-Transition Moisture-Temperature Relationships with a Constellation of Polarimetric Radio Occultation Observations in and near Convection

“…Similar to results at specific tropical locations [8,30], sharp pickups of conditionally averaged P as a function of layer q were noted in different tropospheric layers for a variety of tropical ocean and land regions. More recent studies have refined this relationship via relative contributions to conditional instability from different free-tropospheric layers above the boundary layer, in terms of dynamic entrainment profiles [8,31,32]. Since these convective transition statistics capture the fast time scale associated with convective development, these diagnostics provide a set of constraints on the convective parameterizations used in climate models [6,29].…”

Assimilation of DAWN Doppler wind lidar data during the 2017 Convective Processes Experiment (CPEX): impact on precipitation and flow structure

“…When these downdrafts reach the surface, they spread out, being colder and denser than the surrounding air. This leads to the creation of so-called cold pools -areas that are colder than the surrounding air, causing them to spread radially outward (Schlemmer and Hohenegger, 2014) as density currents. The cold pools created by the individual downdrafts interact with each other, and the mesoscale flow organizes them into bigger entities.…”