Continuing Current in Tower-Initiated Lightning

We investigate 172 upward-initiated negative lightning flashes containing at least one leader-return stroke sequence observed to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. A geometric mean value of 8.75 kA of the return stroke peak current is determined, followed by a continuing current of 1.48 ms with a charge transfer of 0.786 C. We find that in case of the continuing current duration larger than 40 ms, usually defined as long continuing current, or when the continuing current charge transfer is greater than 5 C, the initiating peak return stroke current did not exceed 20 kA. Moreover, continuing currents with durations of less than 20 ms or with a charge transfer smaller than 5 C, those continuing currents were initiated by return strokes with peaks of any range.