Lightning activity variations over three islands in a tropical monsoon region

Abstract

Seasonal, intra-annual and inter-annual variations in electrical activity over three islands (Carnicobar, Little Andaman and North Andaman) of different areas but located in similar synoptic conditions in the south Bay of Bengal are examined from the Tropical Rainfall Measuring Mission (TRMM) satellite observations. The 10-year monthly means of flash density and flash rate mostly increase with the increase in the area of island even on a monthly time scale. Differences in orography/latitudes of the islands with the same area, however, may produce a scatter in this flash density/rate-island area relationship. Present results are, however, not sufficient to resolve between the thermal and aerosol hypotheses for the role of islands in enhancing the lightning activity. However, these can be understood from the interaction of convective activity over the islands with the large-scale monsoon airflow in the region. Annual means of flash density and flash rate do not show any significant change over a period of 10 years. Furthermore, the conclusions of theoretical studies that the strengthening of updraft causes the increase in flash rate in a storm, are upheld in the present analysis.