Parameters of Dart-leader Return Strokes in Artificially-triggered Lightning

摘要

Parameters of dart-leader return strokes in artificially triggered lightning flashes were evaluated based on close electric field and discharge current obtained in Shandong Artificially Triggering Lightning Experiment (SHATLE). The results show that the geometric mean (GM) of return stroke velocity was 2.14×10 8 m/s, which was similar to natural subsequent return strokes. The velocity of dart leaders was an order magnitude smaller than that of the return strokes. The current of dart leaders varied from a minimum of 0.5kA to a maximum of 6.1kA with a GM of 1.86kA. The geometric mean of dart-leader charge density and electrical potential was 71.4 μ C/m and 9.77MV, respectively. There is a positive relationship between dart-leader charge density and return stroke peak current, and the relationship for dart-leader electric potential and return stroke peak current is also the same. The peak current for 5 return strokes in an altitude-triggered lightning named 0504 is estimated, based on the above positive relationship, to be in the 12kA to 39kA range, which is in good agreement with the current range 12-37kA estimated based on the transmission line model. For another two dart-leader return strokes, peak return stroke currents were inferred by using Ampere’s law from the magnetic field. The first one is 39.8kA which agrees well with the result from a Rogowski coil current measurement 41.6kA. The second one is 29.1kA which also agrees well with the Rogowski coil current measurement 29.6kA.