Parameters of Electric Field Waveforms Produced by Positive Lightning Return Strokes

In 2007-2008, 52 positive cloud-to-ground flashes containing 63 return strokes (52 first, 10 second, and 1 third) were recorded at the Lightning Observatory in Gainesville, Florida. The U.S. National Lightning Detection Network located 51 (96%) of the positive return strokes at distances of 7.8-157 km from the field measuring station and correctly identified 48 (91%) of them as cloud-to-ground discharges. In this study, parameters of positive return-stroke electric field and electric field derivative waveforms are examined. The geometric mean (GM) value of initial electric field peak normalized to 100 km for 48 strokes is 18 V/m. The GM peak electric field derivative normalized to 100 km for 27 strokes is 9.0 V/m/μs. The GM zero-to-peak risetime and 10-to-90% risetime for 62 strokes are 6.9 μs and 3.4 μs, respectively, and the GM slow front duration is 5.0 μs. The GM zero-crossing time for 42 strokes is 45 μs and the GM opposite polarity overshoot for 33 strokes is 13% of the peak. These characteristics are compared with those of negative return strokes in Florida found in the literature.