Compact intracloud lightning discharges: 2. Estimation of electrical parameters

We estimated electrical parameters of 48 located compact intracloud discharges (CIDs) using their measured electric fields and vertical Hertzian dipole approximation. This approximation is consistent with the more general bouncing-wave CID model for a reasonably large subset of allowed combinations of propagation speed and channel length. For nine events, we estimated channel lengths from observed reflection signatures in measured dE/dt waveforms and assumed propagation speeds between 2 x 10(8) m/s and 3 x 10(8) m/s, which limit the range of allowed values. For a speed of 2.5 x 10(8) m/s (average value), the channel lengths for these nine events ranged from 108 to 142 m. The corresponding geometric mean values (GM) of peak current, zero-to-peak current risetime, and charge transfer in the first 5 mu s are 143 kA, 5.4 mu s, and 303 mC, respectively. The GM peak radiated power and energy radiated in the first 5 mu s are 29 GW and 24 kJ, respectively. For the remaining 39 events, there were no reflection signatures observed, and the channel length was assumed to be 350 m, for which the Hertzian dipole approximation is valid for speeds in the range of 2 to 3 x 10(8) m/s. In this case, GM values of peak current, zero-to-peak current risetime, and charge transfer in the first 5 mu s are 64 kA, 4.9 mu s, and 142 mC, respectively. The GM peak radiated power and energy radiated in the first 5 mu s are 28 GW and 32 kJ, respectively.