HR: 11:50h
AN: AE51B-05    [PDF]
TI: Possible Interpretations of VLF-LF Radiation Waveshapes Produced at the Initial Stage of Lightning Discharges
AU: * Shao, X
EM: xshao@lanl.gov
AF: Los Alamos National Laboratory, NIS-1, MS D466, Los Alamos, NM 87545 United States
AU: Heavner, M
EM: matt.heavner@uas.alaska.edu
AF: University of Alaska Southeast, 11120 Glacier Highway, Juneau, AK 99801 United States
AB: Observations of lightning discharges from many 10s to a very few 100s of kilometers show that impulsive electric field changes (VLF-LF) can be symmetrically bipolar or asymmetrically "unipolar" at the initial stages of the discharges. The waveshape tends to be more bipolar at the very beginning of the discharges and tends to become increasingly "unipolar" as discharges develop. We suspect that the possible physical reason behind these phenomena is the length of the conducting lightning channel. Each observed radiation pulse is apparently associated with an impulsive breakdown process, which would launch a current pulse propagating backward into the existent conducting channel. As the current propagates, its amplitude is expected to decrease continuously along the channel. At the very beginning of a discharge, the existent channel is short and less conductive, and the breakdown current pulse is attenuated quickly and is effectively constrained into a local range. A current oscillating at a local point will produce a symmetric bipolar radiation pulse. As the discharge develops, the channel becomes longer and more conductive, and a propagating, less attenuated current pulse will produce a radiation pulse similar to the shape of the current pulse itself, or a "unipolar" pulse [Uman et al., 1975]. In this presentation, we will show some field change observations and will compare them with modeled pulse shapes. Reference: Uman, M.A., D.K. McLain, and E.P. Krider, The electromagnetic radiation from a finite antenna, Am. J. Phys., 43, 33-38, 1975.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3360 Remote sensing
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting