Variability of lightning activity in South/Southeast Asia during 1997-98 and 2002-03 El Nino/La Nina events

Impacts of the 1997-98 and 2002-03 ENSOs on total number of flashes and number of flash days from the LIS (Lightning Imaging Sensor) on board the Tropical Rainfall Measuring Mission satellite and on the average flash rate from the combined OTD (Optical Transient Detector) / LIS data are studied in South/Southeast Asia (8° -30°N, 60°-120°E) for the period 1998-2005. Also examined is the difference between the geographical distributions of these parameters in the El Nino period in 1998 and in the corresponding normal period in 1999. During the 1997-98 ENSO event, the number of flashes and average flash rate increase by 12 and 36, respectively, during the El Nino period and during the La Nina period decrease by 22 and 5, respectively, as compared to the corresponding normal periods. Similarly, during the 2002-2003 ENSO event, the number of flashes and average flash rate increase by 28 and 5 during the El Nino period in 2002 as compared to the corresponding normal period. The contrast in lightning activity between the El Nino and La Nina periods is more pronounced in Southeast Asia than in South Asia because of the southeastward shift in the convection activity during the ENSO events. In both regions, however, monthly variations of both total number of flashes and average flash rate are almost parallel to that of surface temperature. Although, the inverse relationship between the Indian Summer Monsoon Rainfall (ISMR) and El Nino broke down in 1997-98, the relationship between the El Nino and lightning maintains its normal increasing trend, indicating that the lightning activity is more sensitive to the convective activity than to rainfall on seasonal time scale. The total number of flashes and aerosol loading increase in the break-period regime as compared to the monsoonal regime. The number of flash days in both ENSO events is higher in the EL Nino phase and lower in the La Nina phase as compared to their normal values in the subsequent years. Enhancement of lightning activity is mostly concentrated over land areas. Our results show that although diurnal variations in lightning activity can be related to the variations in surface temperature, convective adjustment induced by the corresponding ENSO phase needs to be considered for explaining the lightning activity variations on these longer time scales