Dynamics of the Lightning Discharge During the Return Stroke

Summary form only given. Numerous return stroke models have been developed with the aim of enabling a numerical calculation of the radiated lightning electromagnetic pulse (LEMP) and to describe the physics of the gaseous-discharge processes in the lightning channel. Generally taken, all models can be roughly divided into four groups. The first group makes the models based on the modeling of the gas dynamics in the channel during the return stroke. These models involve the solution of hydrodynamics equations representing the conservation of mass, of momentum and of energy, coupled to two equations of state, with the input parameter being an assumed channel current versus time. The second group makes the electromagnetic models usually based on a lossy, thin-wire antenna approximation to the lightning channel. The third group of models is the distributed-circuit models (or R-L-C transmission line models) representing the lightning discharge as a transient process on a vertical transmission line modeled by resistance, inductance and capacitance, all per unit length. The so-called "engineering" models belong to the fourth group. A new generalized lightning traveling current source return stroke model (GTCS) has been developed. The GTCS eliminates completely all shortcomings of the "engineering" lightning return stroke models concerning the current discontinuities and the discontinuities of the current derivative at the place of the return stroke wave-front. As a result of the suitable adopted channel charge distribution function the dynamics of the internal channel processes can be partially examined during the return stroke. Using two-layer cylindrical model of the lightning channel it is possible to derive the simple connection between the channel time-discharge constant and the channel discharge function. The channel time-discharge constant is a function of time and the channel altitude. An example of the possible charge distribution along the channel-base is given enabling the calculation of the channel discharge function and the time-discharge constant. The expression connecting the permittivity and the conductivity of the channel sheath is figured out. Given results enable better understanding of the dynamics of the internal channel plasma processes during the return stroke. Besides, the examination of the channel dynamics is enabled based on the remote measurements of the radiated LEMP as well as on the measured optical signal during the return stroke.