Lightning activity and its association with surface thermodynamics over the Tibetan Plateau

Lightning activity over the Tibetan Plateau, which has an average altitude of higher than 4000 m above sea level, is investigated by using 20-year (1995–2014) LIS/OTD data. The effect of surface thermodynamics on lightning activity is examined for four sub-regions across the plateau based on the NCEP reanalysis data. The average lightning flash density over the entire Tibetan Plateau is 2.5 fl·km−2 yr−1, and the maximum flash density is 7.7 fl·km−2 yr−1 at eastern plateau. The geographical distribution of lightning flash density shows a gradual decrease from east to west across the Tibetan Plateau, from 4.3 fl·km−2 yr−1 on average over the Eastern Tibetan Plateau to 1.7 fl·km−2 yr−1 over the Western Tibetan Plateau. Over the plateau's main highland (>4500 m), there is a local maximum value of 5.7 fl·km−2 yr−1 in the center area of Nagqu. Lightning activity over the Tibetan Plateau mainly occurs in boreal summer, and 96.8% of the annual flashes occur during May–September. There is more lightning in the relatively dry spring, even in summer, over the main highland of the Tibetan Plateau. The results show that humidity and sensible heat fluxes play a vital role in the occurrence of lightning over the Tibetan Plateau. A new parameter, product of rainfall, Bowen ratio (defined as the ratio of the sensible heat fluxes to latent heat fluxes) and surface specific humidity, is proposed and shows a better correlation with lightning activity, generally displaying a larger correlation coefficient than rainfall alone or other parameters over the study sub-regions.