Recovery of the parameters of a lightning current pulse from measurements of the electromagnetic field in the far wave zone

A numerical model of the return stroke of a downward lightning is used to quantitatively analyze the error in recovering the parameters of a lightning current pulse from the electromagnetic field recorded in the far wave zone. It is shown that the error is mainly caused by the deformation of the current wave propagating along the plasma channel from the ground to the cloud and the dependence of the wave phase velocity on the current, rather than by the deviation of lighting from the vertical. The recovery error caused by the nonlinear dependence of the recorded magnetic field on the excitation current can reach a few hundred percent. Results of direct measurements of the lightning current at high-rise buildings and during trigger lightnings cannot be used to calibrate systems for remote monitoring of thunderstorm activity, because radiation from current-carrying metal structures substantially reduces the error caused by the damping of the return stroke wave in the plasma channel.