On the Validity of Approximate Formulas for the Evaluation of the Lightning Electromagnetic Fields in the Presence of a Lossy Ground

Khosravi-Farsani, Mojtaba; Moini, R.; Sadeghi, S.H.H.; Rachidi, Farhad

doi:10.1109/temc.2012.2211364

Cited by 23 publications

(5 citation statements)

References 36 publications

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“…The Finite-Difference Time Domain (FDTD) approach (Yee, 1966) has been widely used for calculating lightning electromagnetic fields generated at different distances from as close as tens/hundreds of meters (Baba & Rakov, 2007a;Mimouni et al, 2008) to as far as hundreds to thousands of kilometers (Berenger, 2005;Tran et al, 2017). The FDTD approach is often employed as a reference method to validate approximate expressions proposed for the computation of lightning electromagnetic fields (e.g., Khosravi-Farsani et al, 2013;Shoory et al, 2011). It has also been used to evaluate the influence of the struck object (e.g., Baba & Rakov, 2008), the building on which field sensors are located (e.g., Baba & Rakov, 2007b), and irregular terrain (e.g., Kobayashi et al, 2016;Li et al, 2014;Li, Azadifar, Rachidi, Rubinstein, Diendorfer, et al, 2016;Li, Azadifar, Rachidi, Rubinstein, Paolone, et al, 2016;Oikawa et al, 2013;Soto et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer

Rachidi

Azadifar

et al. 2019

JGR Atmospheres

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In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M‐component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC‐carrying channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M‐component charge transfer mode (including classical M‐component pulses and M‐component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐component and M‐component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M‐component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M‐component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of...

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Section: Introductionmentioning

confidence: 99%

Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer

Rachidi

Azadifar

et al. 2019

JGR Atmospheres

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“…Li et al [2013Li et al [ , 2014 have analyzed horizontal electric fields above a rough surface of lossy ground at distances of 50 and 100 m from a vertical lightning channel using the 3-D FDTD method. Khosravi-Farsani et al [2013] have computed, using the 3-D FDTD method, horizontal electric fields above and below the lossy ground surface at distances of 100 m to 2 km from a vertical lightning channel and compared the FDTD-computed waveforms with those computed using the Cooray-Rubinstein formula and the Norton approximation [Norton, 1937]. Mimouni et al [2014] have analyzed underground vertical and horizontal electric fields and azimuthal magnetic field within 100 m of the vertical lightning channel using the 2-D cylindrical FDTD method.…”

Section: Introductionmentioning

confidence: 99%

FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters

2015

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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.

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“…In this model, the 3-D finite-difference time-domain (FDTD) is used for performing a full wave analysis of the problem (Elsherbeni and Demir, 2009;Khosravi-Farsani et al, 2013). To circumvent the computational issue associated with the high-memory requirement in this technique, we adopt the parallel processing approach together with a non-uniform meshing scheme.…”

Section: Introductionmentioning

confidence: 99%

Current and radiated electromagnetic fields due to lightning return strokes when hitting elevated objects

Hajebi

Khosravi-Farsani

Sadeghi

et al. 2016

COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

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Purpose Tall towers have a high potential for being struck by lightning which is a major source of electromagnetic radiation with adverse effects on electric, electronic and telecommunication instruments. The paper aims to present an accurate method for predicting the radiated electromagnetic fields and current distribution along the lightning channel and the tower hit by the lightning. Design/methodology/approach The electromagnetic model is utilized to model the lightning channel and the tower is represented by lossy conducting wires. The finite difference time domain (FDTD) method is used to solve for the governing Maxwell’s equations. Due to the large computational space, the FDTD code is paralleled between several computer processors. To enhance the efficiency of the code, a non-uniform mesh is used, reducing the mesh length in the air-ground interface. For model evaluation, simulated current distribution along the lightning channel and tower, and the radiated electromagnetic fields are compared with the measurement data and those obtained using the engineering models. Findings The proposed modeling technique has proved to be more accurate than the conventional methods, particularly in the prediction of current distribution along the tall tower and the vertical component of the radiated electric field. Originality/value The main feature of the proposed technique is its ability to consider the impact of metallic structures in a large space around lightning channel on the predicted radiated electromagnetic fields, having no concern on computer memory requirements.

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On the Validity of Approximate Formulas for the Evaluation of the Lightning Electromagnetic Fields in the Presence of a Lossy Ground

Cited by 23 publications

References 36 publications

Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer

Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer

FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters

Current and radiated electromagnetic fields due to lightning return strokes when hitting elevated objects

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