Modeling CCN Effects on Electrification within High and Low Precipitation Supercells

Abstract

Cloud condensation nuclei (CCN) are known to affect both the electrical and the dynamic evolution of storms, but the effects on storm electrification in different storm modes have not been thoroughly examined. We will detail the impacts of CCN in simulations of the high-precipitation Geary, Oklahoma supercell storm from the Thunderstorm Electrification and Lightning Experiment (TELEX) on 29-30 May 2004, as well as in the simulations of the lower-precipitation Kimball, Nebraska supercell storm from the Stratosphere-Troposphere Experiment: Radiation, Aerosols, and Ozone-A (STERAO-A) on 10 July 1996. The simulations were run and analyzed using five different CCN concentrations (100, 300, 500, 1000, and 2000 cm^-3) in the Collaborative Model for Multi-scale Atmospheric Simulation (COMMAS), a three-dimensional cloud model using a three-moment microphysics scheme with six hydrometeor types, and with a bulk electrification scheme utilizing both inductive and non-inductive charging. The simulations provide details on changes in storm dynamics, kinematics, and electrification as a function of a controlled change in a single variable, the CCN. The CCN concentration of each model run significantly affected the storm dynamics, kinematics, and electrification in both storms. There were differences in storm polarity and charging rates across the different CCN concentrations.

Similar patterns were observed in both case studies. In both case studies, very low CCN concentrations had opposite vertical polarity structure than that of higher CCN concentrations in our control simulations. The overall evolution of the storm also differed with CCN concentration including the spatial extent (horizontal and vertical), lifetime of the storm, as well as the evolution of warm and cold rain processes. These variables were analyzed and compared for both the TELEX and STERAO-A case studies. Upon analysis, differences due to CCN concentration were present regardless of amount of precipitation within the storm. Further sensitivity studies were conducted using two non-inductive charging and microphysics schemes. Results from the simulations of both case studies were compared to observations collected during the TELEX and STERAO-A field campaigns.