Investigations of aerosol impacts on MCSs convection and precipitation: a modeling study

Tuesday, 16 December 2014
Michal Clavner and William R Cotton, Colorado State University, Fort Collins, CO, United States
Mesoscale Convective Systems (MCSs) are important contributors to rainfall in the High Plains of the United States. It is therefore of interest to understand how different vertical distributions and concentrations of aerosols serving as cloud condensation nuclei (CCN) may impact the amount, intensity, and spatial distribution of precipitation produced by MCSs. Unlike ordinary cumulonimbi, MCSs are organized convection systems composed of convective upright updrafts and downdrafts, as well as slowly ascending and descending slantwise motions. These motions can supply moisture to the stratiform-anvil of the MCS without passing through the convective cores. Moreover, the slantwise ascending motions originate some 3-5km above ground level thereby consisting of air with different properties than upright convective updrafts. In order to study the impact of enhanced potential CCN concentrations on MCS precipitation, it is important to understand aerosol microphysical impacts on the dynamics of the different modes of convection within the MCS.

In this study, different aerosol concentrations and their effects on the dynamics of the different modes of MCS convection are examined by simulating a case study using the Regional Atmospheric Modeling System (RAMS). Four simulations were conducted, where each simulation differed in the initial aerosol concentrations as well as their vertical distributions. Previous studies have shown that enhanced aerosols invigorate upright convective updrafts, however, the microphysical effects of increased aerosols and their impact on the dynamics of the slow ascending slantwise motion within an MCS, as of yet, have not been studied. In this presentation, the effects of aerosols on the upright convection, slantwise convection and the resulting impacts on precipitation will be discussed.