Duration and extent of large electric fields in a thunderstorm anvil cloud after the last lightning

Abstract

A series of balloon electric field (E) soundings and time-correlated radar scans through the balloon locations are used to examine the evolution of charge and reflectivity inside a dissipating thunderstorm anvil. The soundings cover a 75 min period during and after the final lightning flash in distant convection. The first sounding measured large E magnitudes (maximum 65 kV m -1) and significant charge densities of both polarities (maximum +2.5 nC m -3) within and screening the anvil. Little change in the maximum E values occurred in the 30 min between the first and third soundings, although altitudes and densities of some charge regions decreased with time (maximum +0.6 nC m -3). Screening charge regions were observed in close coincidence with 12 dbZ radar reflectivity contours, and interior positive charge was found in the reflectivity maxima of both anvil decks. The fourth sounding ascended through visible but optically less dense cloud, and no enhanced E values were detected. Overall, the data indicate the interior positive charge region of the main anvil contained about 150 C and covered at least 250 km 2 nearly 30 min after the last lightning flash. Potentially hazardous E values of 30-35 kV m -1 were measured at 9.9-10.2 km altitude, a common jet aircraft cruising altitude, more than 20 km away from and 32 min after the final lightning flash. About 50 min after the last flash, the main positive charge region contained an estimated 50 C, and potentially hazardous E values associated with the anvil extended over at least 220 km 2. Copyright 2010 by the American Geophysical Union.