Impacts of Aerosol Vertical Location and Concentration on MCS Convective and Stratiform Regions

Mesoscale convective systems (MCSs) are expansive cloud systems that can be separated into convective and stratiform regions. Convective regions are generally associated with strong vertical motion and intense precipitation, while broader stratiform regions are characterized by subsidence in the lower troposphere and rising motion aloft. Due to distinct microphysical and dynamical processes, different latent heating profiles accompany each region, and the strength and location of these latent heating profiles have implications on the surrounding environment and MCS development.

On May 23, 2011, during the Midlatitude Continental Convective Clouds Experiment (MC3E) field campaign, an MCS formed in the Southern Great Plains region of the United States during a period of high aerosol concentrations that advected over the region from Central American biomass burning events. As biomass burning aerosol plumes are transported into the southern United States, the vertical location at which these high aerosol concentrations come into contact with cloud systems varies. Since aerosol particles act as cloud condensation nuclei, their concentrations and location affect microphysical processes and thus latent heating within the MCS. The goal of this study is to understand the impacts of varying aerosol vertical profiles and number concentrations on MCS development.

To reach this goal, simulations of the MC3E May 23 case were completed using the Regional Atmospheric Modeling System (RAMS). First, to address the impact of varying aerosol number concentrations, clean and polluted simulations were conducted. Second, to assess the impact of varying the vertical location of aerosol, profiles with peak concentrations at different levels were used to initialize the simulation. These profiles were determined from locations along the smoke plume transport and were based on model output from the Navy Aerosol Analysis and Predication System (NAAPS) for the May 23 event. All initial aerosol profiles were horizontally homogenized across the domain, and cloud condensation nuclei characteristics and surface absolute number concentrations were constrained by observations from Southern Great Plains site of the DOE's Atmospheric Radiation Measurement (ARM) program. A convective-stratiform separation scheme was used to assess the microphysical processes occurring in each region, and these differentiated processes were compared between sensitivity simulations. The impacts of aerosol vertical distributions on MCS convective and stratiform regions and subsequent implications of such changes will be presented.