Characteristics of the Water-Vapor Field over the Kanto District Associated with Summer Thunderstorm Activities

Abstract

Characteristics of the water-vapor field in relation to thunderstorms onsummer days over the Kanto district in Japan were studied, usingprecipitable water-vapor (PWV) derived from GPS during 2001-2005. PWVaveraged on the active thunderstorm days showed distinct diurnalvariation. In general, hourly data showed that PWV maximum appeared 1similar to 2 hours prior to the maximum thunderstorm activity(precipitation or cloud to ground stroke). The increase of PWV in themountainous region of northern Kanto coincided well with the increase oflow-level wind toward the mountains, which was observed by Wind profilerNetwork and Data Acquisition System (WINDAS).Using the 5 minute data, we further examined the time lag between thePWV and cloud to ground (CG) stroke related to individual thunderstormsin detail. The PWV maxima preceded that of CG stroke by 15 similar to 30minutes, for about 40% of the thunderstorms. In many cases, both PWVand its increment in 30 minutes showed large values within one hourbefore the CG stroke occurrence. This suggested that GPS derived PWVappears to reflect well the local variations associated with athunderstorm.