The Role of Cold Pools in Mesoscale Organization of Shallow Cumulus and Congestus

Abstract:

Cold pool remnants generated by deep convection serve as a stabilizing mechanism against further episodes of convection. Often overlooked, shallower precipitating congestus clouds also generate cold pools at scales ideal for observational study. This study investigates the interaction between showery cumulus congestus and convectively generated cold pools over the ARM SGP (Atmospheric Radiation Measurement Program Southern Great Plains) research site using a multi-sensor observational approach and an ensemble of large-eddy simulation (LES) runs.

On 25 May 2011, the C–band and X-band ARM Precipitation Radars (CSAPR, XSAPRs) sampled a field of precipitating shallow convection and accompanying cold pools. The thermodynamic structure of these cold pools was captured by surface observations around the SGP site, including an AERI-based retrieval that yields lower-atmospheric profiles of temperature and moisture. For this event, observations from the ARM scanning radars and vertically pointing sensors (TSI, cloud radar, ceilometer) reveal cold pools produced by precipitating congestus clouds and suggest modest suppression of congestus development across the cold pool interiors. Viewing sequences from ARM scanning radars sensitive to drizzling clouds provide limited evidence for preferential cloud development along cold pool boundaries. The generated cold pools for this event are weak (~2–3 K), but not particularly shallow (~750 m in depth). LES results are employed to establish the joint relationships between cold pool and cloud properties, in particular the effect of cold pools on the shallow cumulus field and further generation of precipitating congestus clouds.