Merging Cumulus Updrafts

The updrafts that produce deep cumulus clouds have long been conceptually viewed and parameterized as only interacting indirectly, through their collective effects on the large-scale fields of temperature, water vapor, condensate, and horizontal wind. However, it is known that when updrafts develop in close proximity it is possible for them to merge, and thereby produce a larger and less rapidly entraining updraft compared to its precursors. Updraft merging at some height above cloud base level may be able to explain several puzzling features of near-cloud-base updraft properties. Updraft merging is favored by situations that congregate updrafts, such as gust fronts produced by convective cold pools. We are analyzing large-eddy simulations of deep convection to determine the importance of updraft merging and the factors that favor its occurrence. We are also considering how to incorporate the effects of updraft merging in cumulus parameterizations.