Lightning discharges can radiate electromagnetic waves over a wide frequency range from a few Hz to many tens of MHz, but most of the electromagnetic energy is radiated in the ELF and VLF bands.A new approximate method for lightning-radiated extremely low-frequency (ELF) and very low-frequency (VLF) ground wave propagation over intermediate ranges (within 1500 km) was presented in this paper.In our approximate method the field attenuation function was divided into two factors in frequency domain representing the propagation effect of the earth conductivity and curvature, respectively, and these two attenuation factors have more clear and simple expressions in frequency domain, which can be easily calculated by multiplying them rather than solving complex differential equation related to Airy functions.The method was validated by using Newton-Raphson root-finding method for propagation path with different earth conductivities, we found our approximate method could predict the field peak and waveform rise time with a satisfactory accuracy.The comparison results show that our new approximate method can predict the lightning-radiated field peak value over the intermediate range with a satisfactory accuracy within maximum errors of 0.2%, 3.3% and 8.7% for the earth conductivity of 4 S·m-1, 0.01 S·m-1 and 0.001 S·m-1, respectively.So, the research result has solved it in a more efficient way.We also found that the earth curvature has much more effect on the field propagation at the intermediate ranges than the earth finite conductivity.For example, the lightning-produced field peak of ELF/VLF frequency propagating over a spherical-earth is just about 30%~40% of that propagating over a planar-earth at a distance of 1500 km, and 75%~80% for a distance of 500 km.we should pay more attenuation to the effect of earth curvature, for example, the current moment peak value predicted from the measured far field peak will be underestimated when using a far-field-current relationship at the assumed planar earth.
FENG Jianwei
,
HOU Wenhao
,
FAN Xue
,
WANG Lei
,
ZHOU Lei
,
XIAO Dong
. Simulation Analysis of Lightning-Return Stroke ELF/VLF Ground Wave Propagation over Intermediate Ranges[J]. Plateau Meteorology, 2018
, 37(4)
: 1102
-1109
.
DOI: 10.7522/j.issn.1000-0534.2018.00047
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