Lightning strikes to tall objects: Currents inferred from far electromagnetic fields versus directly measured currents

Abstract

We have derived far-field-to-current conversion factors for lightning strikes to tall objects for (1) the initial peak current at the object top, (2) the largest peak current at the object top, and (3) the peak current at the object bottom. These far-field-to-current conversion factors are needed for proper interpretation of peak currents reported by lightning detection networks and are each expressed here as the product of (a) the far-field-to-current conversion factor for lightning strikes to flat ground based on the transmission line model and (b) an appropriate correction factor to account for the transient process in the strike object. The correction factors for the three considered cases are: (1) ftallini.top = v/(v + c), (2) ftall_ini.top = [1 + ρbol(1 + ρtop)] v/(v + c), and (3) ftall_bot = (1 + ρbot) v/(v + c), where ρbot and ρtop are current reflection coefficients at the object bottom and at the object top for upward-propagating waves, respectively. Copyright 2007 by the American Geophysical Union.