Electrical measurements over active thunderstorms

During the summer of 1986, the air conductivity and the vertical electric field were measured over active thunderstorms from a high altitude U-2 airplane. The conductivity at 20 km remained relatively steady above storms with variations less than + or - 15 percent while vertical electric fields in excess of 5 kV/m were regularly observed. Estimates of the storm generator current and the C.T.R. Wilson (i.e., conduction) current can be obtained using the current densities derived from the conductivity and field measurements and integrated over area. Upward flowing currents of 0.05 to 7.7 A were observed with an average of 2.2 A. More importantly, the U-2 data show that the storm current varies linearly with flash rate, therefore, the average charge transfer per discharge should be independent of storm development or activity.