Relating Lightning Features and Topography over the Tibetan Plateau Using the World Wide Lightning Location Network Data

Abstract

 Lightning features over the Tibetan Plateau were studied in relation to topography using the World Wide Lightning Location Network (WWLLN) dataset obtained from April 2009 until December 2014. To describe the strength of lightning strokes, lightning strokes with energies above the 90th percentile (7666 J) were defined as strong lightning (S-lightning) strokes, and the ratio of S-lightning strokes to the overall number of lightning (O-lightning) strokes was defined as the strong ratio (S-ratio).
 O-lightning density over the Tibetan Plateau was found to be high in general, except over the western part of analysis region. Minimum-density zones were observed along the Himalayas approximately 6 km above sea level and in deep valleys within the Tibetan Plateau. The maximum- and minimum-density zones also exhibited maximum and minimum annual rainfall amounts, respectively. S-lightning strokes were also found to frequently occur over the Tibetan Plateau, and most S-ratios in the analysis units exceeded 30 %, which corresponds to three times the global mean. In particular, the S-ratios over the southern part of the Tibetan Plateau, including the Himalayas, were found to be high (50 %) and to correspond with the zone that had the minimum O-lightning density.
 The maximum O-lightning density was observed to occur during the summer at an elevation approximately 0.2-1.0 km higher than the plateau level. The O-lightning and S-lightning densities around the Nagqu sonde station were negatively correlated with the Showalter stability index (SSI) and the vertical wind shear. The S-ratio and average stroke energy were found to be negatively correlated with the vertical shear but not with the SSI.