Generation of Summer Thunderclouds in the Northern Kanto Area, Japan. Partⅰ: First Echo Generation

Abstract

Doppler radar observations were carried out to investigate thundercloud generation in the northern Kanto area from July to September 1997. At the end of August 1997 when the upper thermal trough was passing over central Japan, the initial thunderclouds (first echoes) were generated mainly in the evening, at the foot of mountains below 1000 m. Many of the first echoes were generated at an altitude of 4-5 km (A.G.L.). In regard to the relationship between the altitude of first echo generation and Cloud to Ground (CG) flashes, the first echoes, which were generated at 6 km A.G.L. (at the altitude of-10 °C), brought CG flashes at the highest rate. The case study of 29 August 1997 showed that many thunderclouds developed quickly over Mt. Akagi, north of Maebashi city in the northern Kanto area, and the CG flashes occurred actively both under the strong echo region (32 dBZ and over) and weak echo region (under 32 dBZ) in the life cycle of the echo cells.