Modeling Structure, Dynamics, and Emission of Compact Intracloud Discharges

Abstract:

A new model of the compact intracloud discharge (CID) is suggested. CID is considered as a result of coupling of two (or more) bipolar streamer structures developed in the strong large-scale electric field inside the thundercloud. The model implies two stages of the CID development. At the preliminary stage, in the region of local enhancement of the electric field (between the main negative and upper-positive charge regions or between the upper-positive and overlying negative screening charge regions of the thundercloud) two or more bipolar streamer structures appear successively. The streamer structures are described in the framework of the self-consistent fractal model. The formation time of the structures depends on the properties of the constituent conducting channels and can reach tens of milliseconds. The spatial and time synchronization of the streamer structures is provided by significant altitude variation of the electric field with a scale height of a few hundred meters. As possible physical mechanisms of such variation, the large-scale turbulence of the cloud medium or flow instability can be considered. It is shown that a single streamer structure accumulates significant electric charges of both signs near the ends of the structure during its development. The main stage of CID starts when the electric coupling arises between the developed streamer structures. Then the accumulated electric charges at the adjacent ends of the structures are neutralized for the time, which is substantially less than duration of the preliminary stage. It is shown that parameters of the current pulse at the main stage of the model event are in a good agreement with known properties of the CID current obtained in the transmission line approximation. Taking into account the small-scale fast electric processes at the preliminary and main stages of CID, the model also naturally explain the basic properties and synchronization of the CID emission in the LF/VLF and HF/VHF frequency ranges.