The spatiotemporal variability of lightning activity in the Himalayan foothills

Abstract

[1] 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 5043 m to 219 m. 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 18.75 N-36 N and 68.75 E-93.75 E 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.

The lightning activity associated with the dry and moist convections in the Himalayan Regions

“…Such accumulations of ice particles have also been reported to be positively correlated with CAPE and the updraft speed Rutledge et al, 1992;Zipser, 1994;Petersen et al, 1996]. Our results of the empirical orthogonal function (EOF) analysis show that 22% changes in flash rate in the Himalayan foothills can be associated with variability in CAPE [Penki and Kamra, 2012a].…”

“…In the tropics, lightning responds sensitively to surface temperature at many sites [Williams, 1992], and flash rate tends to be maximum at the time of peak cloud height [Frost, 1954;Williams, 1991]. Recent study of Penki and Kamra [2012a] shows that lightning flash rate is highly correlated with surface temperature in the Himalayan foothills of the northwestern India. This association in specific locations and meteorological regimes is attributed to the gravitational energy of large ice particles in the upper regions of the storm.…”

Lightning and middle atmospheric discharges in the atmosphere

“…Deep convection may result into towering clouds up to the tropopause leading to the possibility of enhanced lightning activity. However, CAPE is not the sole parameter to control lightning activity as is evident from the fact that for the same value of CAPE over land surface and warm ocean water, maritime lightning activity is much reduced (Lucas et al, 1994;Kandalgaonkar et al, 2005;Tinmaker et al, 2010;Kumar and Kamra, 2012;Siingh et al, 2015). One of the reasons may be difference in conversion efficiency of CAPE to updraft kinetic energy.…”

“…This suggests that surface properties are not the only cause of difference in convective processes over continents and oceans. Kumar and Kamra (2012) considered three sea regions (Arabian Sea (AS), Bay of Bengal (BB) and Chinese Sea (CS)) and two land regions (the Peninsular India (PI) and Indo-China Peninsula (ICP)) and showed that the flash rates over peninsular region (PI and ICP) are 2.6-33 times of those over sea regions (AS, BB, CS). The flashes occurring over oceans are more energetic than those occurring over peninsulas.…”

Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

“…We do not identify diamond because our quench rates are too high, however, we do synthesise concentric shell fullerenes that may serve as nanoscopic pressure cells to vapour-deposited (CVD) diamonds (Banhart and Ayajan, 1996;Sorkin et al, 2011). The Luobusa ophiolite in Tibet where the unusual mineral assemblages are documented in most detail is situated at an altitude in excess of 4000 m, in a region where lightning strikes are frequent (Kumar and Kamra, 2012). The lithologies in which UHP and ultra-reduced minerals are found -serpentinised harzburgite and podiform chromitite -are electrically highly conductive lithologies and prone to attract lightning strikes.…”