Study on Waveshapes of Continuing Currents and Properties of M-components Observed in Natural Negative and Positive Cloud-to-ground Flashes Using a High-speed Camera
This work analyses the waveshapes of continuing currents and parameters of M-components in both negative and positive natural cloud-to-ground flashes through videos obtained using a high-speed video system.The dataset is composed by on y long continuing currents (with duration longer than 40 ms)and was selected from more than 500 flashes recorded in S.José dos Campos (45.864 °W,23.215 °S,alt.630 m),southeast of Brazil.All recordings were made using a RedLake MotionsScope 8000S digital high-speed camera with its frame rate set to 1000 fps,exposure time of 1.0 ms,triggered recording with duration of 2.0 s for each flash and GPS time synchronization (stamped on each frame).This feature allowed us to make a comparison with the data obtained by the Brazilian Lightning Location System (BrasilDat)in order to determine the polarity of each flash. Studies on tower measurements have shown that there is a linear correlation between current and luminosity of the flash within the range of current values observed in continuing currents (tens to hundreds of kiloampères). Based on that fact,we have developed a computational algorithm that analyzes each pixel inside the region of the flash channel,calculates their average value for each frame recorded by the high-speed camera and plots a luminosity-versus-time graph.There ’s only one study on waveshapes of continuing currents in the literature based on direct current measurements of triggered ightning.They have classified them in four types according to some general characteristics.We have observed waveshapes that could not be included in any of the four types presented before and it was necessary to introduce two new types.This is the first work on this subject for natural ightning and it also includes positive flashes.We also have used the luminosity-versus-time graphs to observe the occurrence of M-components and measure some parameters (duration,elapsed time and time between two successive M-components).We have plotted a histogram of the M elapsed time over the total duration of the continuing current,as far as we know it was never presented in the literature.The occurrence follows an exponential decay (correlation coefficient:0.99)and it was possible to observe that nearly 25％of the M-components occur in the first 10％of the duration of the continuing current and more than 75％in the first half.
Leandro Z.S.Campos Marcelo M.F.Saba Osmar Pinto Jr. Maurício G.Ballarotti
National Institute for Space Research – INPE,,S.José dos Campos,SP,P.O.Box 515,12201-970,Brazil;Sāo National Institute for Space Research – INPE,,S.José dos Campos,SP,P.O.Box 515,12201-970,Brazil
国际会议
第13届国际大气电学会议(The 13th International Conference on Atmospheric Electricity)
北京
英文
2007-08-13（万方平台首次上网日期，不代表论文的发表时间）