Modeling of lightning generated electric field transitional processes

A new quasi-electrostatic model of high altitude electric field generation due to the lightning - induced change of a thundercloud electric structure is presented. The key point of the model is the assumption that a highly co nducting channel arises due to a cloud - to - ground (CG) discharge, which brings the ground potential to a region near the cloud bottom in some tens of milliseconds after the discharge initiation. Substantial increase in the electric field strength above the thundercloud at this moment is found. A horizontal extension of the lightning channel is taken into account in the framework of the bidirectional model of the channel propagation. This geome try provides a substantially bigger electric field perturbation than the si mplest geometry of the vertical lightning channel does.