The lightning return-stroke initiation point as an ultra-wideband source

Understanding the early growth of the lightning discharge is important because that part of the discharge evolution establishes the high-frequency transmissions from lightning. In this paper, we extend the work from ICEAA 2009 on quantitatively describing the radial charges, fields and currents from the relaxing environment between leader and return stroke events. The purpose of this work is to establish the initial conditions to be used later in detailed modeling of the return stroke initiation. The ICEAA 2009 work used a constant conductivity assumption. This paper will extend that work by describing the role of nonlinear conductivity, including a 3-species model, in the charge relaxation process. Finally, these currents are used in a simple field model.