Effect of urbanization on lightning over four metropolitan cities of India

In the recent years the effect of urbanization on local convections and lightning has been studied very extensively. Here we have analyzed the last 8 years (from 2001 to 2008) data of total lightning, Aerosol Optical Depth (AOD) and rainfall over two inland and two coastal metropolitan cities of India, to study the effect of urbanization on lightning. The lightning and rainfall data are taken from TRMM satellite and AOD data is taken from Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra (EOS AM) and Aqua (EOS PM) satellites. Our analysis shows that both the inland cities show considerable enhancement, where as both the coastal cities do not show enhancement in lightning, in the last 8 years. The results show that, over a inland city, where aerosol concentration is not increased appreciably in last few years the enhancement in convective activity and lightning is controlled by thermodynamic effect, where as, where aerosol concentration show increasing trend, aerosols play major roll in enhancement in lightning activity. It has been also found that over a city where aerosol concentration show increasing trend, lightning show a sharp increase due to combined positive effect of thermodynamics and aerosols, however rainfall show only small increase because of negative effect of aerosols on rainfall. The analysis of lightning, aerosols and rainfall over coastal cities do not show any increasing trend in rainfall and lightning activity which suggest that during premonsoon period all these parameters are controlled by large scale processes and therefore heat island effect or aerosol effect are not observed in both the coastal cities.