Statistical Analysis of Temporal and Spatial Distribution of Cloud-to-Ground Lightning in Japan from 2002 to 2008

Temporal and spatial distributions of cloud-to-ground (CG) lightning in and around Japan were examined for 7 years (2002-2008) using lightning location data from the Lightning Detection Network System (LIDEN) operated by the Japan Meteorological Agency. The frequency of CG flashes was found to be high over the land area in summer. For winter, many of CG flashes were located along the coast of the Sea of Japan of central Honshu (Hokuriku area) and off the coast of the Pacific side (Kanto-Tokai area). The ratio of positive CG flashes to total CG flashes is less than 10% both over the land and the sea in summer, while it is about 40 % over the sea and about 30 % over the land in winter. A detailed analysis for the Hokuriku and the Kanto-Tokai areas has revealed diurnal variations characterized by a peak in the afternoon (15 - 18 LT) in the inland areas, and a peak in early morning (05 – 08 LT) in coastal and offshore areas of the Hokuriku region in summer. For winter, the diurnal variation of CG flash density is indistinct in the Hokuriku area, where CG flashes are largely confined within 20 km of the coastline, while it has a maximum in the early morning (00 - 05 LT) off the coast of the Kanto-Tokai region.