Quantification of Cloud Condensation Nuclei Effects on the Microphysical Structure of Continental Thunderstorms Using Polarimetric Radar Observations

Aerosols serving as cloud condensation nuclei (CCN) are crucial to the microphysical structure of thunderstorms. They can also alter the rate of cloud microphysical processes, the moisture profile and the local temperature as a result of latent heating/cooling in the early stage of thunderstorm development. Continental thunderstorms are characterized by high complexity and are highly influenced by environmental conditions. The purpose of this study is to determine the influences of CCN concentration on the microphysics of continental thunderstorms, using a sample of storms from northwestern Oklahoma. The Weather Surveillance Radar-1988 Doppler (WSR-88D) at Vance Air Force Base (KVNX) was upgraded to dual-polarimetric capabilities in March 2011. Using polarimetric variables, a technique using ArcGIS (Geographic Information System) is used to identify the mean droplet characteristics. An estimate of the mean droplet size from the freezing level to 0.5 km above and the warm updraft depth above the ambient freezing level is developed for 36 continental thunderstorms within 15-20 minutes of convection initiation. Data from the Atmospheric Radiation Measurement (ARM) program at the Southern Great Plains (SGP) site are used to represent the aerosol concentration of the thunderstorm environment, and model soundings from the Rapid Update Cycle (RUC) and Rapid Refresh (RAP) Model are used to describe the storm environment. The RUC/RAP soundings were located approximate 59 km away from KVNX and were selected to represent the undisturbed far-field environment. Previous observational and modeling studies found effects of CCN concentration on thunderstorm characteristics including stronger updrafts as a result of enhanced latent heating, suppressed rain drop collision and coalescence, and altering the cold pool size. The results of this study provide more substantial observational evidence in support of these prior findings. Advisor: Matthew S. Van Den Broek