EXPONENTIAL DISTRIBUTION OF THE CLOUD-TO-GROUND LIGHTNING FLASH DENSITY: LLS RESULTS IN CHINA'S THREE GORGES AREA IN A DECADE, 2000～2009

摘要

The Mean value of Lightning flash Density is used as a criterion to assess the Lightning Stroke Risk, e.g. transmission line and building. Theoretically, the mean value approximates to the expectation value of lightning flash densities in a certain region, as long as the record time of the lightning data is long enough. We analyze the density characteristics of 1.27 million Cloud-to-Ground (CG) lightning flashes recorded by Lightning Locating System (LLS) in China's Three Gorges Area (110°～112.5°E, 30°～32°N) during a decade (2000-2009). Exponential distribution is assumed to describe the frequency distribution of lightning flash densities in the decade. Single-grid random sample and expanded-grid sample are used to validate the hypothesis. And the mean and the standard deviation (STDEV) of lightning flash densities are also compared in the whole area (because Mean and STDEV of exponential distribution are equal). We propose to take the bigger one in Mean and STDEV as the expectation of lightning flash densities. It provides a better correlation with historical record of lightning flashover point than the mean lightning flash density, on 220kV Ge-Chen (from Gezhouba to Chenjiachong transformer substation) electric transmission line in this decade.