Electric fields produced by Florida thunderstorms

Electric fields produced by air mass thunderstorms have been recorded at 25 field mill sites at the NASA Kennedy Space Center (KSC) during the summers of 1975 and 1976. Time- and area-averaged fields produced by individual storms are typically −0.8 to −2.1 kV m−1 during periods of intense lightning activity and usually 2–4 times larger (−2.3 to −4.3 kV m−1) in the final, less active storm periods. The total number of lightning discharges generated by individual storms ranged from 8 to 1987. The average flashing rate per storm was 0.3–9.3 discharges per minute. Large storms tend to evolve through an initial, an active, and a final phase of electrical activity. The average point discharge computed during the active period is 3–4 times less than that computed during the final phase. In 1975, about 71% of all lightning discharges occurred during active storm periods, which in turn represented only about 27% of the total storm durations. In general, the structures of the electrostatic fields produced by lightning discharges in Florida were found to be similar to those in other geographical locations. During active storm periods, 42–52% of all lightning discharges were to ground, and during a final storm period only about 20% were to ground. The fraction of discharges to ground which contained continuing currents ranged from 29 to 46%; the mean duration of 239 ground flashes was about 420 ms. The average density of lightning flashes to ground during 1974 and 1975 at KSC was about 6 km−2 month−1 during the months of June and July.