The spatiotemporal variability of lightning activity in the Himalayan foothills

Abstract

The spatiotemporal variability of lightning activity in the region of the Himalayan foothills and perpendicular to it has been examined from about 16-year data from the TRMM satellite. The monthly mean flash rate for the period from 1995 to 2010 is maximum in an arc-shaped area along the Himalayan foothills and decreases on both the north and south sides of it. Seasonal variation of mean flash rate changes from annual to semiannual as the area shifts from north to south of the Himalayas and the average elevation of area decreases from 5043m to 219m. Further, the mean flash rate is higher in the afternoon and lower from midnight to midday. In the Himalayan foothills, the mean flash rate is highly correlated with surface temperature but poorly correlated with the convective available potential energy (CAPE). Lightning flashes occurring in the high-altitude regions, as compared to the low-altitude regions, are less energetic but more frequent. The empirical orthogonal function (EOF) analysis has been applied to three different data sets of flash rates, surface temperature, and CAPE in the 18.75N-36N and 68.75E-93.75E area for the period of 1995-2010 to examine the relationship between these parameters in terms of seasonal variations in this region. Spatial distributions of the first mode of flash rate and CAPE and of the first and second modes of surface temperature indicate that the Himalayan range exerts a strong effect on the flash rate distributions in this region. However, while the first mode of spatial distribution of flash rate is in phase with the surface temperature, the time series of CAPE and flash rate are out of phase for the first mode but in phase for their second modes. This result amounts to that 65% of variability in CAPE cannot be associated with the changes in flash rate but 22% of CAPE variability can be associated with changes in flash rate. Higher values of flash rate in the Himalayan foothills are suggested to be associated with the diurnal cycle of a mountain breeze front. Relative roles of convective activities due to solar heating of land, orography of the region, and the synoptic convective systems embedded in monsoon current are discussed to explain the results. © 2012. American Geophysical Union. All Rights Reserved.