Microphysical impacts on convective storm dynamics

Variations in the microphysical characteristics of convective storms can impact updraft and downdraft strengths both through buoyancy and precipitation loading effects. Such microphysical variations may be caused by changes in the vertical wind shear, entrainment, relative humidity and aerosol concentrations. The impacts of enhanced cloud condensation nuclei (CCN) on several aspects of deep convective storms will be presented, including the strength of the convective updraft both within the warm rain and mixed phase regions of the storm, as well as the downdraft strength and its subsequent impacts on the longevity of left-moving supercells.

Aerosol indirect theory suggests that enhanced CCN concentrations suppress warm rain formation. This allows for greater amounts of cloud water to be lofted vertically within the storm, which, upon freezing, will release more latent heat than in cleaner environments, all else being equal. The added latent heat release has positive feedbacks to the buoyancy, thereby strengthening the updraft. However, the associated enhancements in cloud and ice water mass will also have a negative impact on the updraft strength through precipitation loading. The competing impacts of these two effects within a deep supercell storm will be examined through the use of cloud-resolving model simulations. Enhanced CCN concentrations also impact the strength of the downdrafts and associated cold pool through their influence on the size of rain droplets and various ice species. This is observed to influence the longevity of the left-moving supercell in these simulations. The mechanisms influencing the left-mover lifetime will be discussed.