Five-year study of cloud-to-ground lightning activity in Yunnan province, China

摘要

The characteristics of cloud-to-ground (CG) lightning in Yunnan province, based on the data recorded by the Yunnan Lightning Detection Network (YNLDN), are presented. The data, more than 2.09 million CG flashes, cover the entirety of Yunnan province and were recorded from 2006 to 2010. The spatial analyses (total and positive flash density, the percentage of positive flashes, negative and positive peak currents) were done with a resolution of 20 km. The average spatial distribution shows a maximum (3.8 flashes km~(-2)yr~(-1)) over the central Yunnan province and Jinsha river associated with topography and cold air mass passage. The mean monthly variation shows a maximum CG lightning between May and October (94%) and minimum values in December and January. High values (0.15 flashes km~(-2)yr~(-1)) for positive CG lightning density are observed in Red river basin. The monthly distribution of positive flashes shows a main maximum in April (19%) and a secondary maximum in July and August (17%), suggesting that positive flashes tend to occur earlier in the year than total flashes. The mean annual percentage of positive flashes has lower values at 3% in the central parts of the province. The percentage of positive CG flashes changes over the year from 2% in August to 49% in January. The monthly variation of median peak current for the negative first-stroke for each month varies only slightly from 27 kA. The monthly variation of the median peak current for positive first-stroke, however, has a maximum in winter and the minimum occurs in May. The mean diurnal cycle for the negative CG lightning flashes peaks between 1600 and 1700 LT (11.37%) and shows a minimum between 0900 and 1000 LT (0.23%). The diurnal variation of positive flashes, in turn, shows a maximum around 0100-0200 LT, with a secondary peak at 1800 LT. This variation is associated with local mesoscale circulation, which has an obvious nocturnal feature.