LATENT HEATING AND AEROSOL-PRECIPITATION INTERACTIONS WITHIN MESOSCALE CONVECTIVE SYSTEMS
February 23, 2016
Hosted by Sue van den Heever (advisor), Sonia Kreidenweis (co-advisor), Russ Schumacher, Richard Eykholt (Physics)
Two studies are presented in this thesis that focus on understanding cloud processes within simulations of two mesoscale convective system (MCS) events that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E). Simulations are conducted with the Regional Atmospheric Modeling System (RAMS) and are compared with a suite of observations obtained during MC3E. It is concluded that the simulations reasonably reproduce the two MCS events of interest. Both studies provide information that can assist in the advancement of cloud process parameterizations in atmospheric models.
The first study details the microphysical process contributions to latent heating profiles within MCS convective and stratiform regions and the evolution of these profiles throughout the MCS lifetime. Properly representing the distinctions between the latent heating profiles of MCS convective and stratiform regions has significant implications for the atmospheric responses to latent heating on various scales. The simulations show that throughout the MCSs, condensation and deposition are the primary contributors to latent warming, as compared to riming and nucleation processes. In terms of latent cooling, sublimation, melting, and evaporation all play significant roles. Furthermore, it is evident that throughout the MCS lifecycle, convective regions demonstrate an approximately linear decrease in the magnitudes of latent heating rates, while the evolution of latent heating within stratiform regions is associated with transitions between MCS flow regimes.
The second study addresses the relative roles of middle-tropospheric and lower-tropospheric aerosol particles on MCS precipitation during the mature stage. A suite of sensitivity simulations for each MCS event is conducted, where the simulations are initialized with different aerosol profiles that vary in the vertical location of the peak aerosol particle number concentrations. Importantly, the total integrated aerosol mass remains constant between the different initialization aerosol profiles, and therefore, differences between the simulated MCS precipitation characteristics can be more directly attributed to the varied vertical location of the aerosol particles. The simulations from both MCS events demonstrate that during the mature stage, the concentrations of lower-tropospheric aerosol particles are the primary factor in determining the intensity of precipitation 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 is not consistent between the two simulated MCS events, suggesting that the MCS structure and environmental conditions play important roles in regulating the impacts of middle-tropospheric and lower-tropospheric aerosol particles on MCS precipitation. Lastly, changes in precipitation processes can result in dynamical feedbacks that further modify, and hence complicate, the net effect of aerosol particles on MCS precipitation. One such feedback process involving the MCS cold pool intensity and updraft tilt is discussed.