Possible role of aerosols in the charge structure of isolated thunderstorms

The electric field and Maxwell current density measured below 32 small isolated thunderstorms over Pune (India) have been analyzed here. These data clearly show the presence of 10 out of 32 thunderstorms with inverted polarity charge structure. Values of Aerosol Optical Depth (AOD) on thunderstorm days taken from MODIS show that all the thunderstorms with inverted polarity occurred on days with significantly higher AOD compared to normal polarity thunderstorms. The peak flash rate did not show significant difference between normal polarity thunderstorms and inverted polarity thunderstorms. The dew point depression (DPD) during pre-monsoon thunderstorms shows good correlation with inverted polarity charge structure. Observations suggest that aerosol concentration plays an important role in the formation of inverted polarity charge structure in these thunderclouds. In presence of high aerosol concentration with adequate ice nuclei non-inductive charging mechanism can produce strong and wide spread positive charge region in the lower portion of cloud. However, observed good correlation of DPD with inverted polarity charge structure in the pre-monsoon period suggest that the effect of high cloud base height on inverted polarity charge structure as suggested by Williams et al. (2005) cannot be ruled out