Resolution requirements for modeling streamer formation in a spark gap

Summary Form only given, as follows. The authors have derived the charge conservation equation in a general form from Maxwell´s equations. From experimental estimates of streamer conductivities and propagation velocities in atmospheric air, they have inferred appropriate temporal and spatial scales to be approximately 0./3 ns and approximately 0.3 cm. Assuming the electron impact ionization is the dominant mechanism changing the conductivity so abruptly and using the best available rate coefficient data, they obtained an estimate of the maximum E field of approximately 80 kV/cm. These orders of magnitude are relatively insensitive to model details. Extending the order-of-magnitude analysis, they estimated the effect of spatial gradients in the electron conservation equation, and both the current rate of change and electron pressure gradient terms in the momentum conservation equation, to be perturbations at worst on the local homogeneity and mobility approximations. Thus, simple fluid models should be adequate. However, preliminary numerical analyses have shown that photoionization may be indispensable in producing simulated ionization wave propagation speeds, in agreement with experimental observations.<>