科研之友
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摘要
We have computed lightning electromagnetic pulses (LEMPs), including the azimuthal magnetic field H-phi, 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 mu s), and ground conductivity (ranging from 0.1 S/m to infinity) on H-phi, 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-phi, 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-phi and E-z are only slightly influenced by it. The peaks of H-phi 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 S/m.
- 出版日期2015-8-27
