Climatology of lightning flash activities over Sri Lanka

Seventeen years of remotely sensed satellite mounted Lightning Imaging Sensor (LIS) data were used to determine the characteristics of lightning activities over Sri Lanka. From 1998 to 2014, there were 12.5 million lightning flashes over the land mass covered by Sri Lanka. There is an increasing trend in the intensity of lightning activities with 22,000flashesyear(-1). The annual cycle of lightning flashes shows a clear spatial difference of lightning activities during the southwest and northeast monsoon seasons. The highest occurrence of lighting activities is confined to the highly populated western region of the island while the coastal areas in the northern and eastern regions and central hills show relatively low occurrences. The estimated maximum cloud to ground lightning flash density was 53flashesyear(-1)km(-2) and the average being 7.7flashesyear(-1)km(-2). The density of lightning in the wet zone tends to be twice as much compared to the dry zone. The onset and retreat of lightning seasons are February 25 through May 15 for the warm season which coincides with the first inter-monsoon season and July 31 through November 19 for the cold season which coincides with the latter part of the southwest monsoon season and second inter-monsoon season. Based on thunder day measurements, it is shown that a simple linear relationship can be used to estimate lightning flash densities from thunder days. We have also examined the relationship between lightning flash activities and sea surface temperature over the Arabian Sea and the Bay of Bengal and conclude that sea surface temperature can be used as a proxy to estimate change in lightning activities as sea surface temperatures have strong persistence in the temporal characteristics.