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722 results on '"Rakov, Vladimir A."'

9. Lightning, the Science

Author

Rakov, Vladimir A., Angrisani, Leopoldo, Series Editor, Arteaga, Marco, Series Editor, Panigrahi, Bijaya Ketan, Series Editor, Chakraborty, Samarjit, Series Editor, Chen, Jiming, Series Editor, Chen, Shanben, Series Editor, Chen, Tan Kay, Series Editor, Dillmann, Rüdiger, Series Editor, Duan, Haibin, Series Editor, Ferrari, Gianluigi, Series Editor, Ferre, Manuel, Series Editor, Hirche, Sandra, Series Editor, Jabbari, Faryar, Series Editor, Jia, Limin, Series Editor, Kacprzyk, Janusz, Series Editor, Khamis, Alaa, Series Editor, Kroeger, Torsten, Series Editor, Li, Yong, Series Editor, Liang, Qilian, Series Editor, Martín, Ferran, Series Editor, Ming, Tan Cher, Series Editor, Minker, Wolfgang, Series Editor, Misra, Pradeep, Series Editor, Möller, Sebastian, Series Editor, Mukhopadhyay, Subhas, Series Editor, Ning, Cun-Zheng, Series Editor, Nishida, Toyoaki, Series Editor, Pascucci, Federica, Series Editor, Qin, Yong, Series Editor, Seng, Gan Woon, Series Editor, Speidel, Joachim, Series Editor, Veiga, Germano, Series Editor, Wu, Haitao, Series Editor, Zamboni, Walter, Series Editor, Zhang, Junjie James, Series Editor, and Gomes, Chandima, editor

Published
2021
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12. Continuing Current Seen Above and Below the Cloud: Comparing Observations From GLM and High‐Speed Video Cameras.

Author

Ding, Ziqin, Zhu, Yanan, Lapierre, Jeff, DiGangi, Elizabeth, Ringhausen, Jacquelyn, Lauria, Paola B., Saba, Marcelo M. F., Rakov, Vladimir A., Abbasi, Rasha U., da Silva, Diego R. R., and da Silva, Tagianne P.

Subjects
OPTICAL instruments, CAMCORDERS, LOGISTIC regression analysis, LIGHTNING, REGRESSION analysis
Abstract

This study assesses the reliability and limitations of the Geostationary Lightning Mapper (GLM) in detecting continuing currents by comparing observations from ground‐based high‐speed cameras with GLM‐16 data. Our findings show that the GLM's one‐group detection efficiency (DE_1) is 53%, while the more stringent five‐consecutive‐group detection efficiency (DE_5) is 10%. Optical signals detected by the GLM predominantly occur during the early stages of continuing currents. Additionally, there is a notable disparity in detection efficiencies between positive and negative continuing currents, with positive continuing currents being detected more frequently. The application of the logistic regression model developed by Fairman and Bitzer (2022) further illustrates the limitations in continuing current identification. The study underscores the challenges of relying solely on satellite data to monitor and analyze continuing currents, emphasizing the need for advancements in detection technologies and methodologies to reliably detect continuing current at a large spatial scale. Plain Language Summary: This study investigates continuing current in cloud‐to‐ground lightning—a prolonged electrical discharge known for causing significant damage, such as igniting large‐scale wildfires. For the first time, we used recordings from ground‐based high‐speed cameras to assess how effectively the Geostationary Lightning Mapper (GLM), an optical instrument on the GOES satellite, detects these currents. Our findings reveal that the GLM often captures only the early stages of continuing currents and struggles to detect them consistently, particularly those in weaker, negative types of lightning. These results underscore the limitations of current satellite‐based optical instruments in fully monitoring continuing currents, emphasizing the need for improved methods to better detect and understand these electrical discharges and mitigate their impacts. Key Points: The Geostationary Lightning Mapper is limited in detecting continuing current, with a one‐group DE of 53% and a five‐group DE of just 10%Optical signals captured by the Geostationary Lightning Mapper are predominantly during the early stage of continuing currentsA significant disparity is observed in GLM detection efficiencies between positive and negative continuing currents [ABSTRACT FROM AUTHOR]

Published
2024
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18. Estimation of the Equivalent Impedance of Lightning Return-Stroke Channel From Current Waveforms Measured at Tall Towers

Author

Hasegawa, Masahiro, Kutsuna, Koki, Baba, Yoshihiro, Nagaoka, Naoto, Tsuboi, Toshihiro, and Rakov, Vladimir A.

Abstract

Two waveforms of current measured at a height of 497 m of the 634 m high Tokyo Skytree and three waveforms of current measured at a height of 533 m of the 540-m high Ostankino tower have been reproduced in simulations using the finite-difference time-domain method in the two-dimensional cylindrical coordinate system. The lightning return-stroke channel is represented by a dielectric-coated vertical conductor. The dielectric coating has high relative permeability, such as 20, 40, or 60, and serves to reduce the propagation speed of current wave along the channel-representing vertical conductor and to increase its equivalent impedance relative to that of the vertical conductor without dielectric coating. The channel-representing vertical conductor and the tall tower are excited by a voltage source inserted between them. A procedure to determine the output waveform of the voltage source from measured current waveforms has been developed. The magnitudes of measured initial current peaks ranged from 5 to 12 kA. The equivalent impedance of the lightning return-stroke channel has been inferred to be roughly 800 to 900 Ω.

Published
2024
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24. The Impacts of Lightning Beyond the Troposphere

Author

Cohen, Morris, primary, Kosar, Burcu, additional, Halford, Alexa, additional, Ringuette, Rebecca, additional, Silva, Caitano da, additional, Bortnik, Jacob, additional, Cohen, Morris, additional, Smith, David, additional, Dwyer, Joe, additional, Morales, Carlos, additional, McHarg, Matthew, additional, Derr, Jason, additional, Kolmasova, Ivana, additional, Mailyan, Bagrat, additional, Albrecht, Rachel, additional, Smith, Jeffrey, additional, Liu, Ningyu, additional, Lang, Timothy, additional, Trostel, John, additional, Boggs, Levi, additional, Marshall, Robert, additional, Molaverdikhani, Karan, additional, Losego, Jessica, additional, Rowland, Douglas, additional, Abbasi, Rasha, additional, Wang, Tao, additional, Goodman, Steven, additional, Mann, Ian, additional, Thomas, Jeremy, additional, Bhaskar, Ankush, additional, Riousset, Jeremy, additional, Wada, Yuuki, additional, Price, Colin, additional, Guerra-Garcia, Carmen, additional, Xu, Wei, additional, Janalizadeh, Reza, additional, Krehbiel, Paul, additional, Neubert, Torsten, additional, Celestin, Sebastien, additional, Ebert, Ute, additional, Farges, Thomas, additional, Ripoll, Jean-Francois, additional, Esman, Teresa, additional, Garay, Michael, additional, Fung, Shing F., additional, Rakov, Vladimir, additional, Kaeppler, Stephen, additional, McCollough, James, additional, Lay, Erin, additional, and Sharma, A. Surjaal, additional

Published
2023
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32. A Procedure to Infer Lightning Return-Stroke Current Waveform From Far-Field Waveform for the Case of Lossy Ground

Author

Koike, Shunsuke, Fukuyama, Masahiro, Baba, Yoshihiro, Tsuboi, Toshihiro, and Rakov, Vladimir A.

Abstract

We proposed expressions for reconstructing the waveform of channel-base current from the corresponding far electric field waveform (radiation field component only) on perfectly conducting ground for the modified transmission line models with linear and exponential current decay with height. Waveforms of vertical electric field on lossy ground at far distances (50–200 km) were computed using the finite-difference time-domain (FDTD) method for solving discretized Maxwell's equations in the 2-D cylindrical coordinate system. The FDTD-computed waveforms of vertical electric field on lossy ground were compensated for propagation effects and used in the proposed field-to-current conversion expressions for inferring the channel-base current waveform. The reconstructed currents are in excellent agreement with the current used in computing the fields on lossy ground.

Published
2024
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42. High‐speed video observations of needles in positive cloud-to-ground lightning flashes

Author

Wu, Bin, Weitao, Lyu, Qi, Qi, Ying, Ma, Lyuwen, Chen, and Rakov, Vladimir

Abstract

High‐speed video data were used to analyze the initiation and propagation of needles and their associated flickering events observed in positive cloud‐to‐ground (+CG) flashes. Needles occurred during the return‐stroke later stage and the continuing current. They initiated near the lateral surface of the positive leader channel and extended almost perpendicular to that channel. Flickering events are recoil type streamers (or leaders) that retrace the channels created by needles. Needles are caused by the radial motion of negative charge from the hot core of the positive‐leader channel into the positive corona sheath surrounding the core, when the core is rapidly recharged (its radial electric field reversed) by the return‐stroke process and during the following continuing current. Needles could evolve into self-propagating negative leaders. Self-propagating negative leaders evolving from needles exhibit stepped development via connection of space stems/leaders to the tips of negative leaders. The occurrence of space stems/leaders and their connection to the tips of needles resulting in the continuous extensions of needle channels play an important role in the evolution of needles into self-propagating negative leaders., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

49. Energetic Radiation from Subsequent-Stroke Leaders : The Role of Reduced Air Density in Decayed Lightning Channels

Author

Kereszy, Istvan, Rakov, Vladimir, Czumbil, Levente, Muresan, Alexandru, Ding, Ziqin, Micu, Dan, Cooray, Vernon, Kereszy, Istvan, Rakov, Vladimir, Czumbil, Levente, Muresan, Alexandru, Ding, Ziqin, Micu, Dan, and Cooray, Vernon

Abstract

Featured Application Electric fields produced by lightning subsequent stroke leaders are sufficiently high for acceleration of electrons to relativistic speeds, leading to generation of X-rays/gamma-rays as a result of Bremsstrahlung emissions. Leaders of subsequent strokes in negative cloud-to-ground lightning are known to produce X-ray/gamma-ray emissions detectable at distances of a few kilometers or less from the lightning channel. These leaders usually develop in decayed but still warm channels of preceding strokes. We computed electric field waveforms at different points along the path of subsequent leader as those points are traversed by the leader tip. For a typical subsequent leader, the electric field peak is a few MV/m, which is sufficient for production of energetic radiation in a warm (reduced air density) channel. We examined the dependence of electric field peak on the leader model input parameters, including the prospective return-stroke peak current (a proxy for the leader tip potential) and leader propagation speed, and compared model predictions with measurements.

Published
2022
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