The modeling of channel current in the lightning return stroke

The return‐stroke current in a lightning flash to ground is modeled as the response of an initially charged, uniform transmission line to the application of a terminating resistance at one end of the line. For a lossless line, the consequent current is constant between abrupt changes; this current differs substantially from that given by the common modeling procedure of injecting a double‐exponential current pulse into one end of a uniform line. The inclusion in the model of resistive losses along the line produces a current that retains the abrupt initial onset, but has a more realistic decay than the decay of the double‐exponential pulse. The fields associated with such a current in a vertical channel agree reasonably well with those observed.