Modeling of Streamer Ignition and Propagation in the System of Two Approaching Hydrometeors

First-principles plasma fluid modeling is used for investigation of electrical gas discharges ignited by a configuration of two approaching conducting hydrometeors with typical radii on the order of several millimeters under thunderstorm conditions (i.e., at an elevated location in the Earth's atmosphere corresponding to half of air density at ground level and at applied electric field approximately half of that required for avalanche multiplication of electrons in air). It is demonstrated that ultraviolet photons produced by the electrical discharges developing due to the electric field enhancement in the gap between two hydrometeors and resultant photoionization in the discharge volume lead to much less stringent conditions for conversion of these discharges to a filamentary streamer form than in the case not accounting for the effects of photoionization. It is also demonstrated that this photoionization feedback is critical for understanding and correct description of the subsequent streamer discharges developing on the outer periphery of two hydrometeors whose potential is equalized due to the electrical connection established by the initial streamer discharge between them. The initial streamer ignition between the hydrometeors can be preceded by the corona development, which can have detrimental effect on the ignition. However, it is demonstrated that for hydrometeors approaching with a speed of (Formula presented.) 10 m/s the effect of this onset corona is small.