Download or read book Initiation of Streamers from Thundercloud Hydrometeors and Implications to Lightning Initiation written by Samaneh Sadighi and published by . This book was released on 2015 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electric field values measured inside thunderclouds have consistently been reported to be up to an order of magnitude lower than the value required for the conventional electrical breakdown of air. This result has made it difficult to explain how lightning frequently occurs in thunderclouds. A few different theories have been offered to explain the lightning initiation process, one of them being the theory of lightning initiation from hydrometeors. According to this theory, lightning can be initiated from electrical discharges originating around thundercloud water or ice particles in the measured thundercloud electric field. These particles, called hydrometeors, can cause significant enhancement of the thundercloud electric field in their vicinity, increasing the probability to initiate streamers that are precursor discharges for the hot lightning leader channel. The first step in improving our understanding of lightning initiation is to study streamers. For this dissertation research, we have focused our efforts on studying streamer initiation and propagation from thundercloud hydrometeors. For the first part of this study, we have further investigated the idea proposed by Liu et al. [2012b] to study streamers from ionization column hydrometeors in thundercloud conditions. We have performed simulations for ambient electric field values of 0.5E[k] at thundercloud altitudes, and obtained successful streamer formation, confirming the work of Liu et al. [2012bJ. Reducing the ambient electric field to as low as 0.3E[k] affects the streamer's ability to propagate stably. According to our results, initiation of stable streamers from thundercloud hydrometeors in a 0.3E[k] electric field is possible, only if enhanced ambient ionization levels (e.g., the ionization created by corona discharges around the same or other nearby hydrometeors) are present ahead of the streamer. The magnitude and distribution of this ambient density may be a determining factor on whether the streamer forms, or branches during initiation. The branching of the streamer interrupts the stable streamer propagation and changes the dynamics of the streamer. We investigate the streamer branching behavior and characteristics, and test a theory that has recently been proposed to explain this phenomenon [Savel'eva et al., 2013]. We find that the geometry of the streamer head plays an important role in the streamer branching phenomena. The fast radial movement of the maximum streamer head curvature, combined with the slow reduction of the maximum curvature value, eventually leads the streamer head to branching. In order to verify whether an ionization column is a proper representation of a dielectric hydrometeor, for the second part of this dissertation we modify our streamer discharge model to accommodate an isolated dielectric particle representing the hydrometeor inside the computational region. Since the governing equations of the plasma discharge model are discretized on a uniform rectangular grid, the boundary cells do not conform to the shape of the dielectric. We utilize a boundary-cut cell method proposed by Ye et al. [1999] to handle these cut cells, and properly evaluate the corresponding fluxes. A boundary condition capturing method by Liu et al. [2000] has been used to properly enforce the electrostatic boundary conditions on the dielectric hydrometeor. The development of this model has enabled us to accurately simulate the discharges around dielectric hydrometeors with various shapes and physical states. Streamer discharge results obtained from the dielectric hydrometeor have been presented and compared with the results obtained from the first part of this work. We compare our modeling results with laboratory experiments and realistic thundercloud conditions and discuss the implications of this study to lightning initiation and other lightning related phenomena.