Regional variability in lightning activity over South Asia

The regional variability of lightning activity over 10 different regions, selected with at least one major meteorological/topographical feature, of South Asia (8 degrees N-36 degrees N, 90 degrees E-100 degrees E) have been examined on all time scales from the data obtained from July 1995 to December 2013 from the Tropical Rainfall Measuring Mission satellite. A comparative study of the correlation coefficients calculated between lightning flash rate and convective parameters, aerosol optical depth (AOD) and topography for different regions is carried out. Impact of the progress of the Asian Monsoon on the spatio-temporal variability of flash rate is also examined. Monthly-averaged variations are annual at the regions >2,700 m in altitude and are semi-annual at the regions <2,700 m in altitude. The annually averaged flash rates increase during the study period in most of the regions. However, such long-term changes are nonlinearly related to the change in convective parameters and AOD and such inter-relationships differ from one meteorological region to another. Small changes in AOD in high altitude regions are associated with very large changes in the surface temperature and flash rate. The flash rate is strongly correlated with surface temperature in the dry region of the north-west but with CAPE in moist region of the north-east. Progress of the Asian monsoon strongly impacts the flash rate in different regions. Ratio of the amplitudes of primary to secondary maxima at land stations increases with latitude in case of the monthly-averaged variations in flash rate. The primary maxima in these variations are highly correlated with the atmospheric surface temperature. However, the secondary maxima are associated with the low-level convergence during the withdrawal phase of the monsoon. Incursion of moisture by the Bay of Bengal branch of monsoon current determines the sequence of occurrence of lightning activity in different regions along the Himalayan foothills and north-west.