Land-sea contrast in lightning activity over the sea and peninsular regions of South/Southeast Asia

The land-sea contrast in lightning activity between three sea regions of the Arabian sea (AS), the Bay of Bengal (BB) and the Chinese sea (CS) and two land regions of the Peninsular India (PI) and the Indo-China Peninsula (IP) has been studied from the 11-year (1995 to 2005) data obtained from the Optical Transient Detector (OTD) and Lightning Imaging Sensor (US) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. Lightning activities in different sea regions and over different peninsular regions are also compared with each other. The values of flash rate over peninsular regions (PI and IP) are 2.6 to 33 times of those over sea regions (AS, BB, CS). Although this contrast is seen throughout the year it is more dominant in the premonsoon and postmonsoon seasons. Seasonal variations of the monthly-averaged values of the average flash rate are semiannual in all regions with one maximum in April/May and another in October. The two peaks in semiannual variations are attributed to the variation in surface air temperature. In addition, the October peak may have some contribution from the unstable thermodynamic conditions during the withdrawal phase of the summer monsoon. The annual flash rate shows an increasing trend of 1.1 to 1.2 times increase in both land and sea regions in South Asia but no significant change in the regions in Southeast Asia during the 1995-2005 period. The monthly-averaged flash rates are positively correlated with the average surface temperature and convective available potential energy (CAPE) and negatively correlated with the outgoing longwave radiation (OLR), with higher correlation coefficients over peninsular regions than over the sea regions. The flashes over peninsular regions, though more frequent, are likely to be less energetic and have only 0.4 to 0.9 of the radiance that is found over the sea regions. The lowest flash rate in the AS region can be attributed to the dominance of more maritime conditions with shallower clouds in monsoon season in this region. (C) 2012 Published by Elsevier B.V.