Difference in the lightning frequency between the July 2018 heavy rainfall event over central Japan and the 2017 northern Kyushu heavy rainfall event in Japan

Abstract

Abstract The causes for the differences in the lightning frequency between two heavy rainfall events, the 2017 northern Kyushu heavy rainfall event and the 2018 heavy rainfall event in central Japan, were examined using a numerical model coupled with an explicit bulk lightning model. These heavy rainfall events occurred near the Baiu frontal system of Japan in July, but the characteristics of rainfall differed. The former case was categorised as an extreme rainfall and extreme convective event by previous satellite observational studies, and the lightning frequency was high. Conversely, the latter case was categorised as an extreme rainfall without extreme convection event, and the lightning frequency was low. The numerical model used in this study successfully reproduced the differences in the lightning frequency between the two cases. Our analyses indicated that the differences in the lightning frequency between the two cases were attributed to the differences in the vertical structure of the charge separation rate and the charge density, which originated from the difference in the vertical distribution of graupel.

Keywords

• bulk lightning model
• heavy rainfall events
• lightning frequency
• numerical model