Using Low-level Currents Measured during Lightning Events to Estimate Upward Leader Properties

Low-level currents measured prior to return strokes can potentially provide information about the properties of upward leaders during lightning flashes. However, these currents need to be properly analysed and interpreted in order to be useful for evaluating upward connecting leaders. In this paper, low-level currents measured before return strokes in two lightning events to two structures in Brazil are analysed and interpreted as case studies. The discharge current estimated from one of these events is used as input to a detailed thermohydrodynamic model with an extensive kinetic scheme for N ₂ /O ₂ mixtures. The model allows the evaluation of the physical and chemical properties of upward connecting leaders. Estimates of the temperature, mass density, electric field and radius of the channel are presented for an upward connecting leader propagating in a lightning event. In addition, estimates of the axial density of electrons, ions and neutral particles (including NO and NO ₂ ) are also reported.