An equivalent attenuation function for the computation of the lightning field radiated by a tortuous channel

The electromagnetic lightning field is usually computed by considering a model consisting in a vertical and rectilinear channel, as well as a Transmission-Line (TL) type propagation characterized by an attenuation function, which expresses how the current decreases while it travels upward along the lightning channel. When dealing with realistic channels, affected by tortuosity, the current attenuation is usually neglected and the field computation is cumbersome, since the discretization of the channel in a large number of linear segments has to be performed. This contribution presents an equivalent attenuation function to be used in the computation of vertical channels in order to reproduce the results of a tortuous one. The attenuation function is computed by solving an inverse problem through the Tikhonov regularization technique, and it is found to be reliable for distances larger than 5 km from the lightning channel.