The results are given of an experimental investigation of a cathode-directed streamer discharge in synthetic air in the pressure range from $760\text{to}300\text{torr}$ and their comparison with the results of direct numerical simulation in a 2D hydrodynamic approximation. The pattern of discharge branching upon variation of pressure is investigated experimentally. The results are given of comparison of the predicted and measured values of anode current, streamer propagation velocity, and channel diameter. It has been demonstrated that the electric field in the streamer head is hardly affected by the pressure decrease, while the electron concentration decreases with pressure by an order of magnitude. At the same time, production of chemical species in a cathode-directed streamer discharge varies at a rate of at least the second power of inverse pressure.

Observations of a shock wave propagating through a decaying plasma in the afterglow of an impulse high-voltage nanosecond discharge and of a surface dielectric barrier discharge in the nanosecond range were analysed to determine the electron power transferred into heat in air plasmas in high electric fields. It was shown that approximately half of the discharge power can go to heat for a short (∼1 µs at atmospheric pressure) period of time when reduced electric fields are present at approximately 10³ Td. A kinetic model was developed to describe the processes that contribute towards the fast transfer of electron energy into thermal energy under the conditions considered. This model takes into account previously suggested mechanisms to describe observations of fast heating in moderate (∼10² Td) reduced electric fields and also considers the processes that become important in the presence of high electric fields. Calculations based on the developed model agree qualitatively with analyses of high-voltage nanosecond discharge observations.