Measurements of initial potential gradient and particle charges in a Montana summer thunderstorm

An Aerocommander aircraft made three passes through a small isolated thunderstorm on July 19, 1981. These passes were made at a temperature of −5°C and were in conjunction with other aircraft at different altitudes. The Aerocommander was equipped to measure the vertical component of the ambient potential gradient, particle charge, particle size and character, cloud liquid water content, temperature, and vertical velocity. Evidence is presented for the association of charge with ice particles. The development of the potential gradient in relation to movement of these ice particles is discussed. In general, the highest charge densities, of order −0.5 C km −3 , were coincident with regions of high graupel concentration and the highest potential gradients, of order −15 kV m −1 , were measured below regions with the highest radar reflectivities. Only a small fraction (<10%) of ice particles were found to be charged significantly (>±5 pC), but these were found even at the earliest stages of electrification. The results are compared to concepts derived from recent laboratory experiments on the charge produced during ice particle collisions.