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FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters
Author(s) -
Aoki Masanori,
Baba Yoshihiro,
Rakov Vladimir A.
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd023245
Subject(s) - physics , finite difference time domain method , wavefront , electric field , ranging , lightning (connector) , dimensionless quantity , computational physics , optics , mechanics , geodesy , geology , power (physics) , quantum mechanics
We have computed lightning electromagnetic pulses (LEMPs), including the azimuthal magnetic field H φ , vertical electric field E z , and horizontal (radial) electric field E h that propagated over 5 to 200 km of flat lossy ground, using the finite difference time domain (FDTD) method in the 2‐D cylindrical coordinate system. This is the first systematic full‐wave study of LEMP propagation effects based on a realistic return‐stroke model and including the complete return‐stroke frequency range. Influences of the return‐stroke wavefront speed (ranging from c /2 to c , where c is the speed of light), current risetime (ranging from 0.5 to 5 µs), and ground conductivity (ranging from 0.1 mS/m to ∞) on H φ , E z , and E h have been investigated. Also, the FDTD‐computed waveforms of E h have been compared with the corresponding ones computed using the Cooray‐Rubinstein formula. Peaks of H φ , E z , and E h are nearly proportional to the return‐stroke wavefront speed. The peak of E h decreases with increasing current risetime, while those of H φ and E z are only slightly influenced by it. The peaks of H φ and E z are essentially independent of the ground conductivity at a distance of 5 km. Beyond this distance, they appreciably decrease relative to the perfectly conducting ground case, and the decrease is stronger for lower ground conductivity values. The peak of E h increases with decreasing ground conductivity. The computed E h /E z is consistent with measurements of Thomson et al. (1988). The observed decrease of E z peak and increase of E z risetime due to propagation over 200 km of Florida soil are reasonably well reproduced by the FDTD simulation with ground conductivity of 1 mS/m.