MIEM HSE Scientists Come Closer to Unraveling the Mystery of Cloud Lightning Movement
At the general meeting of the Russian Academy of Sciences (RAS), held on April 23, research by Alexander Kostinskiy, Vladimir Rakov and Mikhail Andreev conducted in collaboration with their colleagues from academic institutes on the modeling and development of lightning was acknowledged as one of the most significant Russian scientific achievement in 2018.
At the Russian Academy of Science’s general meeting held on April 23, Academy President Alexander Sergeev presented a report of the major breakthroughs in Russian science. He particularly noted the findings of Alexander Kostinskiy, Deputy Director of HSE Tikhonov Moscow Institute of Electronics and Mathematics (MIEM HSE), Vladimir Rakov, Professor of the University of Florida and Leading Research Fellow of MIEM HSE, and Mikhail Andreev, Engineer of the Faculty of Physics, who, in collaboration with colleagues from the RAS Institute of Applied Physics, the VNIITF High-Voltage Center, and the Chinese Academy of Meteorology, conducted a series of studies on the development of lightning leaders. (The research is published in the following articles: Kostinskiy et al., 2018, JGR Atmospheres, v.123, 10* and Rakov et, al. 2018, IEEJ, v.138, 5**).
As the President of the Russian Academy of Sciences noted, lightning has long been an area of intense inquiry, but since it is extremely difficult to study in natural conditions, studies thus far have not been able to provide a detailed picture of the development of lightning leader steps. Studying a long spark with the aid of high-voltage generators, however, can give an idea.
It is known that, in nature, 90% of lightning is negative, that is, it is borne out of predominantly negatively charged parts of thunderclouds. High-speed cameras can show how hot negatively charged plasma channels, which are called negative leaders, move of clouds and move in abrupt steps to the ground. When a negative leader comes close to the ground, it initiates positive ascending leaders, which ascend towards it from high structures and trees. When a descending negative leader collides with an ascending positive leader, a single bright channel emerges between the cloud and the earth—this is what we know as a lightning bolt. From this collision, a wave of potential shoots upward and downward. The lightning channel heats up to 40 thousand degrees Celsius, rapidly expands and causes thunder.
But 10% of the discharges that reach the ground are positive, and they are more dangerous, since they cause a longer discharge with a higher energy input, and lightning rods are not able to provide very good protection against them. Most scientists believed that the positive lightning leaders move continuously or in very small steps, as opposed to the large steps of negative leaders.
When modeling lightning flashes on a high-voltage (6 MV) stand, researchers for the first time were able to obtain detailed images with high spatial resolution of the abrupt steps of positive leaders and negative leaders with nanosecond exposure. Consequently, a new hypothesis was formed about the formation of abrupt steps of positive leaders in a corona streamer burst, and X-ray fluxes from this area were measured.
These results allow scientists to interpret with much more accuracy the results of radio measurements of leading lightning channel plasma movements at high altitudes, which cannot be recorded with high-speed cameras, and thus better understand the nature of lightning propagation in storm clouds.
* Kostinskiy, A.Yu., V. S. Syssoev, N. A. Bogatov, E. A. Mareev, M. G. Andreev, M. U. Bulatov, D. I. Sukharevsky, and Rakov V. Abrupt Elongation (Stepping) of Negative and Positive Leaders Culminating in an Intense Corona Streamer Burst: Observations in Long Sparks and Implications for Lightning, Journal of Geophysical Research-Atmospheres, 2018, vol. 123. No. 10. P. 5360-5375, doi: 10.1029/2017JD027997
** Rakov, V. A., E. A. Mareev, M. D. Tran, Y. Zhu, N. A. Bogatov, A. Yu. Kostinskiy, V. S. Syssoev, W. Lyu. High-Speed Optical Imaging of Lightning and Sparks: Some Recent Results, IEEJ Transactions on Power and Energy. 2018, vol.138, no.5, pp.321-326, doi: 10.1541/ieejpes.138.321
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