HR: 0830h
AN: AE21A-1102    [PDF]
TI: Attenuation Of Current Wave Propagating Along A Perfectly Conducting Wire: Application To Lightning
AU: * Baba, Y
EM: ybaba@mail.doshisha.ac.jp
AF: Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611 United States
AU: * Baba, Y
EM: ybaba@mail.doshisha.ac.jp
AF: Department of Electrical Engineering, Doshisha University, Kyotanabe, Kyoto, 610-0321 Japan
AU: Rakov, V A
EM: rakov@ece.ufl.edu
AF: Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611 United States
AB: In this study, using the finite-difference time-domain (FDTD) method for solving Maxwell_fs equations, we demonstrate that a vertical phased array of current sources above perfectly conducting ground, activated as prescribed by the transmission line (TL) model with return-stroke speed equal to the speed of light (v = c), produces a spherical TEM wave, identical to that analytically derived for the TL model with v = c by Thottappillil et al. [2001]. (This can be viewed as a proof of validity of the FDTD method used here.) Then, we apply the same approach to the case of a lumped current source at the bottom of a vertical perfectly conducting wire above perfectly conducting ground and show that the current wave launched by the current source propagates upward with attenuation and that the resultant field structure is non-TEM, as also follows from other lightning return stroke models based on solving Maxwell_fs equations. The attenuation is stronger for shorter current pulses and for current sources of smaller length. Thus, it appears that the basic assumption of the TL model (no current attenuation with height) is inconsistent with Maxwell_fs equations, unless the lightning channel is viewed as a phased array of current sources. It is inconsistent with the transmission line theory either, since a vertical wire above ground constitutes a non-uniform transmission line, whose characteristic impedance varies with height. We will try to explain the mechanism of current attenuation on a vertical perfectly conducting wire above perfectly conducting ground, usually attributed to radiation losses, on the basis of the electromagnetic field theory. In particular, we will discuss the interaction of the electromagnetic field produced by the source with the vertical conductor and ground and the direction of resultant Poynting vector. Thottappillil, R., J. Schoene, and M. A. Uman, Return stroke transmission line model for stroke speed near and equal that of light, Geophys. Res. Lett, 28(18), 3593-3596, 2001.
DE: 0619 Electromagnetic theory
DE: 0684 Transient and time domain
DE: 0689 Wave propagation (4275)
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting