Self-Organizing Transport Model of a Spark Discharge in a Thunderstorm Cloud
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Radiophysics and Quantum Electronics, Vol. 63, No. 2, July, 2020 (Russian Original Vol. 63, No. 2, February, 2020)
SELF-ORGANIZING TRANSPORT MODEL OF A SPARK DISCHARGE IN A THUNDERSTORM CLOUD A. A. Bulatov, 1∗ D. I. Iudin, 1,2,3 and A. A. Sysoev 1,2
UDC 519.673+519.172.3+537.321
We propose a small-scale transport model of the electric-discharge tree formation and analyze its implementation for a characteristic case of the thundercloud conditions. The following innovative features of the model can be emphasized: no connection to the spatial grid, high spatiotemporal resolution, and allowance for the asymmetry of the development of the positive and negative streamers and the time evolution of the discharge-channel parameters. The criterion of the streamer-to-leader transition, which is used in this work, is formulated in terms of the channel temperature and is based on the well-known mechanism of ionization-overheating instability, which is universal for the spark discharge. Within the framework of the described approach, a heated well-conducting leader channel is formed by combining the currents of tens of thousands of streamers, so that each of them initially has f negligible conductivity and a temperature that does not differ from the ambient temperature. The model bileader tree has electrodynamic characteristics that are intermediate between those known for the laboratory long spark and the developed lightning, which is expected for an “immature” lightning leader. The morphology and electrical parameters of the calculated discharge tree of the incipient model lightning leader agree with the modern data on the lightning-discharge development.
1.
INTRODUCTION
At present, it is an unquestionable fact that the lightning initiation is preceded by the appearance of a system of positive streamers in a thundercloud (a detailed review of this topic can be found in [1]). However, there is no unique opinion on how the streamer activity leads to the lightning-discharge formation. Numerical models capable of simulating the process of formation of a well-conducting leader channel in a thundercloud that is sufficiently long to maintain its natural development with maximum electric-field strength, which is an order of magnitude lower than the air-breakdown field, do not exist [2]. According to the opinion of the authors, the most comprehensive hypothetical description of the mechanism of formation of the lightning nucleus in a thundercloud is given in [6] with reference to [3–5]. It is assumed that positive streamers are initiated in the region of the intensified field, which emerges during polarization of a single hydrometeor in the external field or during approach of a pair of the oppositely charged hydrometeors. In this case, we assume that the system of the positive streamers, which develops from the hydrometeor, or a set of the overlapping streamer systems, which develop from the neighbor hydrometeors, takes out the positive charge in the growth direction and accumulates the negative charge at the start point. Eventually, th
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