Aerosol Effects on Precipitation and Lightning Activity over Houston, Texas

Cloud-to-ground lightning flash from the National Lightning Detection Network (NLDN) in Houston, Texas shows a higher density over the urban area based on a twelve-year period (1989-2000) analysis. The local enhancement of lightning centered at Houston urban region could be attributed to the urban heat island effect and anthropogenic pollution. A two-moment bulk microphysical scheme has been implemented into the Weather Research and Forecasting (WRF) model to investigate urban aerosol effects on lightning associated with a typical sea breeze frontal event occurring in Houston. The simulated radar reflectivity generally agrees with the observations and the calculated lightning potential index (LPI) exhibits temporal and spatial consistence with lightning flashes recorded by NLDN. Sensitivity study indicates that aerosols greatly enhance lightning activity under the polluted condition. The analysis on the microphysical properties documents that more efficient mixed phase processes and intensified convection under the polluted aerosol condition lead to more efficient graupel-ice collision, which favors electrification and charge separation in thunderstorms. In addition, aerosols suppress the light precipitation process but increase the heavy rain during the studied sea breeze case. The aerosol radiative effects on lightning activity will be examined in the next step through incorporating the aerosol optical properties in the radiative scheme of the model. Urban heat island effect will be investigated in near future as well.