Cloud-to-Ground Lightning Activity in the 10–11 June 1985 Mesoscale Convective System Observed during the Oklahoma–Kansas PRE-STORM Project

Abstract

As part of the field program for the Oklahoma?Kansas PRE-STORM Project conducted in May?June 1985, a network of electromagnetic direction-finders was deployed to locate and detect the polarity of cloud-to-ground (CG) lighting flashes associated with Mesoscale Convective Systems (MCSs). We present an analysis of such data for the 10?11 June MCS. This storm consisted of a line of convective cells trailed by an 80 km wide stratiform precipitation region. Data from the lightning strike locating network, along with both conventional and Doppler radar data, are analyzed over a significant portion of the storm's lifetime to examine the relationship between the storm precipitation structure and the position and polarity of the lighting activity. The majority of the negative CG activity is located in the convective precipitation region. The frequency of negative CG activity is highest around the period of most intense convective rainfall. Positive CG activity is mainly confined to the trailing stratiform region, and there is a correlation between the areally integrated stratiform precipitation and the frequency of positive CG flashes. We propose that the occurrence of positive CG flashes in the trailing stratiform region is a result of the reward advection of positive charge on small ice particles from the upper levels of the convective cells by the storm relative winds. However, charging of hydrometeors may occur within the stratiform region and contribute to the positive space charge. Candidate charging mechanism are discussed.