A new approach to calculate electric fields and charge density distribution when lightning strikes a tall object

•This paper for the first time derives electric field expressions in the monopole technique.•Derive charge density expressions along the tall object and lightning channel.•Very-close range electric fields are calculated based on this new method and compared with the results of traditional dipole technique.•Provide an alternative explanation to the inverse of polarity of the vertical electric field at very close range from the tall object base.

We derive electric field expressions, associated with lightning strikes to a tall object, using the monopole (Continuity Equation) technique which is distinctly different from the traditional dipole (Lorentz Condition) technique. Expressions to calculate the charge density along the tall object and lightning channel based on the assumptions of the transmission line model of the lightning strikes to a tall object and a series point current source placed at the object top, are also derived. These expressions are used to calculate the very close-range electric fields in the monopole (Continuity Equation) technique in terms of the retarded current and charge density along the tower and lightning channel and their results are compared with those calculated from the traditional dipole (Lorentz Condition) technique in terms of the retarded current along the tower and lightning channel. Alternative explanations are provided to the inversion of polarity of the vertical electric field at very close range based on distribution of charge density along the tower and lightning channel.