Shandong Artificially Triggering Lightning Experiment and Current Characterization of Return Stroke

Shandong Artificially Triggering Lightning Experiment (SHATLE) has been conducted continuously since the summer of 2005. During the six years from 2005 to 2010, twenty-two negative lightning flashes containing eighty-eight return strokes were successfully triggered. Channel base currents, close electromagnetic fields, and high-speed camera images were obtained simultaneously for some of the strokes. Based on directly measured currents for thirty-six return strokes, the geometric mean of return stroke peak current was about 12.1 kA with a maximum of 41.6 kA and a minimum of 4.4 kA, the half peak width of current varied from 1 to 68 μs, and the geometric mean values of 10%－90% risetime, charge transfer, and action integral were about 1.9 μs, 0.86 C, and 2.6×103A2?s, respectively. The surface electric field at 30 m away from the discharge channel caused by a return stroke with peak current of 16.5 kA reached 111.9 kV/m. The geometric mean of magnetic field at 60 m away from the discharge channel was about 52 μT. The peak current and charge transfer of some large M components were comparable with those of return stroke. The speed of upward positive leaders in the initial stage of triggered flashes was about 0.96×10.5 m/s.