Electrical and multiparameter radar observations of a severe hailstorm

Abstract

Using data from the 11 cm, CSU‐CHILL multiparameter radar, the simultaneous evolution of the radar‐inferred precipitation structure and electrical characteristics of a severe hailstorm is investigated. We compare the substorm point discharge current, intracloud (IC) lightning flash rate, cloud‐to‐ground (CG) lightning flash rate, ground strike location, and flash polarity to the progression of precipitation types and amounts. This study is unique in that it presents multiparameter radar observations of a thunderstorm complex which exhibited an extremely high IC‐to‐CG ratio (IC/CG, 20–70) and predominantly positive CG lightning (over 74%) after it became severe, producing large hail and weak tornadoes. In particular, we investigate the reported relationship between large hail and positive CG lightning. Although a direct correlation is found between a rapid increase in IC/CG, the first positive CG lightning flashes, and the initial production of hail aloft, the temporal and spatial behavior of large hail and positive CG lightning appear to be anticorrelated, as broad peaks in the positive CG flash rate lag relative maxima in the fallout of large hail by up to 30 min. The majority of positive ground strikes were adjacent to the main precipitation core in a region of light rain and little or no hail at the surface. Aloft, radar data indicated that ice crystals were aligned vertically in a strong electric field. Corona point observations at the surface indicate that these regions adjacent to the convective core were characterized by net positive charge aloft. Possible mechanisms to explain these observations are discussed.