Plasma in the Conducting Channel of Lightning During the Small-Current Stage

Abstract The development of lightning plasma was analyzed for the low-current stage, during the time intervals between the passage of the stepped leader stroke and the return stroke, as well as between the return stroke and the dart leader of the subsequent lightning stroke. It was shown that the equilibration time in the analyzed plasma is short compared to the duration of the slow lightening stages. Therefore, in the plasma of the conducting channel of lightning during the slow stage of its development, a local thermodynamic equilibrium is established, and the plasma temperature in each point is the same for electrons and atoms. According to a gas–dynamic model, the plasma decay time after the return stroke (1 ms) is short compared to the duration of the slow stage (50 ms). Therefore, an external electric field is necessary to maintain the plasma during the slow stage, which generates a weak electric current that stabilizes the plasma in the conducting channel. Taking into account the results of numerical models for the relaxation of the plasma of the return stroke, parameters of heat transfer were determined, which are connected to the thermal conductivity of the plasma inside the conducting channel, mainly due to the transfer of dissociative excitation and the thermal conductivity of electrons. At the boundary of the conducting channel of the lightning, the heat transfer occurs as a result of the convection of surrounding air, which leads to the formation of “tongues” and vortices approximately 10 cm in size. The convection leads to a complete renewal of hot air in the conducting channel with cold air at a temperature of 7 kK over a period of about 40 ms.