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The Three-dimensional Propagation Characteristics of Flash Leaders in the Attachment Process

Author: GaoYan
Tutor: LvWeiTao
School: Chinese Academy of Meteorological Sciences
Course: Atmospheric Physics and Atmospheric Environment
Keywords: natural lightning attachment process three-dimensional reconstructionchannel leader three-dimensional propagation characteristic
CLC: P427.3
Type: Master's thesis
Year: 2014
Downloads: 3
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A two-dimensional (2D) image of lightning channel cannot reflect the real spatialdistribution of three-dimensional (3D) lightning channel and is insufficient to meet theneeds of accurate analysis on the3D lightning channel development characteristics andon the interaction between different leaders. This paper establishes a reconstructionmethod of3D lightning channel from dual-station optical observation. The2Dcoordinate sequence of lightning channel is obtained from each2D lightning imagecaptured at different positions. The theory of solid geometry is used to match thecoordinates from different sequences. Then the3D lightning channel is reconstructedby the matched coordinates.Six downward negative flashes terminated on tall structures in Guangzhou areanalyzed. The3D lightning channels of primary branch of downward leader (PBDL)and upward connecting leader (UCL) are reconstructed. For comparison, thecorresponding2D parameters are calculated using the single-station high-speed images.The main conclusions are summarized as follows:(1) The3-D length values of six UCLs’ reconstructed channels range from180to818m and the average value is426m. The UCL3-D speed values range from0.8to14.3×105m/s and the average value is4.7×105m/s. When the time is approaching thereturn stroke (RS), the propagation speed of UCL is increasing.(2) There are35PBDL3D speed values can be calculated in the attachmentprocess of6natural flashes. The PBDL3D speed values range from0.8to6.8×105m/sand the average value is3.4×105m/s. The PBDL3D speed exhibits no clear trend before0.4ms preceding the beginning of first return stroke and sharply increases.(3) The ratio of the3-D speeds of PBDL and UCL ranges from0.2-3.8and theaverage value is0.9. When the time is approaching the return stroke, the ratio isdecreasing. When the time is less than0.5ms prior to the return stroke,75%of the ratio is less than1.(4) Only using high-speed images obtained from the main station, we candetermine the2D propagation characteristics values of6UCLs and PBDLs. From thestatistical analysis, we determine that the ratio of the3-D to2-D speed ranges from1.1to1.8times.(5) Similar to the variation of speed, the variation of luminosity of the PBDL tipexhibits no clear trend until the final0.2ms prior to the beginning of return stroke,while the luminosity of the UCL tip exhibits an overall increasing trend.

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CLC: > Astronomy,Earth Sciences > Atmospheric science (meteorology ) > Meteorological elements,atmospheric phenomenon > Atmospheric phenomena > Atmospheric electricity phenomena ( atmospheric electricity )
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