Latent Heating, Microphysical and Aerosol Processes of MC3E Mesoscale Convective Systems

Description

A number of cloud-resolving simulations have been conducted of two mesoscale convective systems (MCSs) observed during the Midlatitude Continental Convective Clouds Experiment (MC3E) in order to investigate the latent heating characteristics, and the microphysical and aerosol processes of MCSs. The extensive observational dataset obtained during MC3E was used to both initialize and evaluate the simulations. The simulated output was found to compare well with the observations, and hence used to conduct several different studies. In the first study, the microphysical contributions to MCS stratiform and convective latent heating profiles and the variations of these profiles as a function of storm lifecycle were investigated. The simulations demonstrate an approximately linear decrease in the magnitudes of convective latent heating rates, while the evolution of latent heating within stratiform regions is associated with transitions between the MCS flow regimes. In the second study, the impacts of surface aerosol concentrations on MCS anvil characteristics were investigated. It was found that an increase in the riming removal rates of cloud water for greater aerosol concentrations led to greater precipitation rates and less lofted cloud water mass. Reduced lofted cloud water led to less ice mass but more numerous, small ice crystals in the anvil. In spite of reduced ice mass, the anvil clouds exhibited greater areal coverage, increased albedo, and reduced cloud top cooling. In the third study the relative roles of middle- and lower-tropospheric aerosol concentrations on MCS precipitation was investigated. It was found that the concentrations of lower-tropospheric aerosol particles are the primary factor in determining precipitation intensity near the cold pool leading edge, while middle-tropospheric aerosol particles were entrained within convective updrafts, thus altering the cloud droplet properties. However, the aerosol effects on total surface precipitation was not consistent between the two MCS events, suggesting that the MCS structure and environmental conditions play important roles in regulating the impacts of aerosol particles on MCS precipitation. Finally, in the fourth study, our approach to characterizing the aerosol fields used to initialize and evaluate the model is outlined, and a CCN closure study for the SGP site during the MC3E time period is also shown. Highlights from all 4 studies will be presented.