Investigation of Microphysical Processes Occurring in Organized Convection during NAME

A major objective of the North American Monsoon Experiment (NAME) was to quantify microphysical processes within convection occurring near the steep topography of northwestern Mexico. A previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed-phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes, with an even greater role of melting ice in rainfall production over the highest terrain. Despite the higher frequency of these isolated cells compared to organized convective systems, the latter were responsible for 75% of rainfall. Therefore, this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography. Similar to isolated convection, both warm-rain and ice-based processes played important roles in producing intense rainfall in organized convection. Although similarities existed between cell types, organized convection was typically deeper and contained greater ice mass, which melted and contributed to the development of outflow boundaries. As convection organized along the slopes, these boundaries spread over the lower terrain, converging with diurnally driven upslope flow, thus allowing for the generation of new convection and propagation toward the coast. Once over lower elevations, additional warm-cloud depth contributed to intense rainfall and allowed for continued ice production. This, along with the development of rear inflow in the trailing stratiform region, led to further development of convective outflow, similar to organized systems in the tropics and midlatitudes.