Environmental study of tropical hailstorm and its relationship with negative narrow bipolar event and positive ground flashes

Abstract

The thermodynamic conditions in the environmental storms are derived from the Rapid Update Cycle model analysis, where the point nearest to the storm, in the direction of storm motion was used. This paper presented the evolution (5-minute flash rate) of two tropical hailstorms that occurred in Malaysia at two sites namely Bukit Jalil (approximately 112 km from our station) and Sungai Udang (approximately 22 km from our station) with the objective to understand the relationship of the hailstorms with Negative Narrow Bipolar Event (–NBE) and Positive Cloud-to-Ground (+CG) flashes. The hailstorm occurred in Bukit Jalil on June 3 rd 2016 started at around 08:20 (UTC) and producing hails around 10:30. Negative NBE rate reaches the maximum at around 10:30 to 10.40 with 17 –NBEs recorded when the hails were reported to hit the ground. Within the same time, 15 +NBEs were detected. 75 minutes before the hails hit the ground, 30 –NBEs and 70 +NBEs were detected. In contrast, only 3 +CG were detected. On the other hand, after 10.40 and up to 14.30 (230 minutes), only 5 –NBE were detected compared to 244 +NBEs and 9 +CGs. The hailstorm occurred in Sungai Udang on September 14 th 2016 started at around 17:00 and producing hails around 19:00 to 19:30. Within this 30 minutes duration, 70 +CGs were detected when the hails were reported to hit the ground. 120 minutes before the hails hit the ground, only 4 –NBE were detected compared to 154 +NBEs and 22 +CGs were detected. After 19.30 up to 20.30 (60 minutes duration), 4 +NBEs and 18 +CGs were detected while no –NBE has been recorded. Based on the results of these 2 tropical hailstorms, clearly stronger convection does not related only to higher –NBEs flash rate but also highly correlated to +CGs flash rate.