Initiation locations of lightning flashes relative to radar reflectivity in four small Florida thunderstorms

Abstract

This study examines initiation locations of intracloud (IC) and cloud-to-ground (CG) lightning near Kennedy Space Center, Florida, on 1 day. One unicellular and two multicellular thunderstorms occurred over land, and one multicellular storm was 30 km offshore. The storm over ocean was visible on radar 47-51 min before its first flash (of 17 total); first echoes in the storms over land were 23, 12, and 16 min prior to the first flashes (of 34, 16, and 9 total). Initiation points of 66 flashes were identified using the first initial breakdown (IB) pulse location from electric field change measurements or a VHF source coincident with the first IB pulse; 10 ICs occurred without enough data to similarly locate the initiation. All but 2 of 35 flashes that initiated as negative CGs began below 6.8 km altitude; two higher CG initiations (7.1-7.5 km) were the first CGs in two storms. Initiations of 21 normal ICs occurred above 7.9 km, 6 late stage ICs initiated at 5.5-7.5 km, and 4 hybrid IC-CG flashes initiated as ICs at 6.6-8.1 km. Initiation locations were tightly clustered in small regions of each cell. Over land, early and mature stage flashes initiated within 2 × 2 km in each cell, or about 10-25% of the midlevel reflectivity coverage. One cell over ocean had initiations within 6 × 5 km, less than 30% of its reflectivity area. The IC initiations generally occurred above reflectivity cores, in 15-35 dBZ, and CG initiations were in 30-45 dBZ beside or atop cores.