Abstract
A model of the lightning return stroke is developed using the experimental data presented in Parts I and II and Gilmore's tables for the composition of dry air in thermodynamic equilibrium. The temperature, electron density, pressure, relative mass density, per cent ionization, and specie concentration in a 10-m section of a model-return stroke are given with 5-μsec resolution from 0–30 μsec. During this period, the temperature decreases from 30,000 to 16,000 K and the electron density decreases from 1018 to 1.5 × 1017 cm−3. The channel is characterized by an average pressure of 8 atm in the first 5 μsec and attains atmospheric pressure at approximately 20 μsec. A minimum relative mass density of 3×10−2 is attained at the same time. Per cent ionization is on the order of 100 in the first 15 μsec and then decreases.
The largest nitrogen specie concentration in the 0-15 μsec period is NII, followed by N-III, which in turn is followed by NI, All three concentrations decrease in the 0-15 μsec time period. In the 15-30 μsec period the NI concentration increases, the NII concentration attains a quasi-equilibrium, and the NIII concentration continues to decrease rapidly. The salient characteristics of the model return stroke are discussed and related to spectral observations.
