Analysis of lightning-ionosphere interaction using simultaneous records of source current and 380 km distant electric field

We present simultaneous current and wideband electric field waveforms at 380 km associated with upward lightning flashes initiated from the Santis Tower, Switzerland. To the best of our knowledge, the dataset presented in this study includes the first simultaneous records of lightning currents and associated fields featuring ionospheric reflections for natural upward flashes, and the longest distance at which natural upward lightning fields have been measured simultaneously with their causative currents. The intervals between the groundwave and skywave arrival times are used to estimate ionospheric reflection heights during day and night times using the so-called zero-to-zero and peak-to-peak methods. During daytime, the mean ionospheric reflection heights, obtained using the two different delay estimation approaches, are about 78 and 76 km, corresponding to the D layer. The mean reflection height at nighttime is about 90 and 89 km, corresponding to the E layer. We present a full-wave, finite-difference time-domain (FDTD) analysis of the electric field propagation including the effect of the ionospheric reflections. The FDTD simulation results are compared with the measured fields associated with upward flashes initiated from the Santis Tower. It is found that the model reproduces reasonably well the measured waveforms and the times of arrival of the one-hop and two-hop skywaves relative to the groundwave.

On Lightning Electromagnetic Field Propagation Along an Irregular Terrain

Mohammad Azadifar, Dongshuai Li, Stefan Metz, Mario Paolone, Davide Pavanello, Marcos Rubinstein, Zhaoyang Wang, Qilin Zhang

In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Santis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Santis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Santis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located.

Institute of Electrical and Electronics Engineers2016

Modeling of Different Charge Transfer Modes in Upward Flashes Constrained by Simultaneously Measured Currents and Fields

Mohammad Azadifar, Lixia He, Qi Li, Mario Paolone, Davide Pavanello, Marcos Rubinstein

The purpose of the paper is to investigate charge transfer modes in upward lightning flashes by means of numerical simulation constrained by concurrent observations of electromagnetic fields and currents. In particular, we focus on different types of pulses occurring in upward negative flashes. The MTLE return stroke model is used to compute the electric fields associated with return strokes and mixed-mode pulses, while the M-component model of Rakov et al. (1995) is used to compute electric fields associated with M-components and M-component-type ICC pulses. The simulation results are constrained by experimental data consisting of simultaneous records of lightning currents and electric fields associated with upward flashes at the Santis tower. The inferred velocities for M-component and M-component-type ICC pulses range from 2.0x10(7) m/s to 9.0x10(7) m/s, and the corresponding junction point heights range from 1.0 km to 2.0 km. The inferred pulse velocities for return strokes and mixed-mode pulses range from 1.3x10(8) m/s to 1.65x10(8) m/s. The inferred current attenuation constants of the MTLE model obtained in this study range from 0.3 km to 0.8 km, lower than the value of 2.0 km suggested in previous studies. The obtained results confirm the similarity of mixed-mode charge transfer to ground with return strokes on the one hand, and of the M-component-type ICC with classical M-components mode of charge transfer on the other hand.

2018

An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Säntis Tower

Mohammad Azadifar, Lixia He, Davide Pavanello, Marcos Rubinstein

We present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Säntis Tower in Switzerland. The electric field was measured 15 km from the tower. Upward flashes always begin with the initial stage composed of the upward‐leader phase and the initial‐continuous‐current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return‐stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no‐current time intervals; (2) mixed‐mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively small junction heights; (3) “classical” M‐component pulses superimposed on the continuing current following some return strokes; and (4) M‐component‐type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively large junction heights. We consider a data set consisting of 9 return‐stroke pulses, 70 mixed‐mode ICC pulses, 11 classical M‐component pulses, and 19 M‐component‐type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed‐mode and M‐component‐type pulses, which is based on the current waveform features. The characteristics of M‐component‐type pulses during the initial stage are found to be similar to those of classical M‐component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed‐mode ICC pulses were preceded by microsecond‐scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond‐scale electric field pulses observed for M‐component‐type ICC pulses and which can be attributed to the junction of an in‐cloud leader channel to the current‐carrying channel to ground. Classical M‐component pulses and M‐component‐type ICC pulses tend to have larger risetimes ranging from 6.3 to 430 μs. On the other hand, return‐stroke pulses and mixed‐mode ICC pulses have current risetimes ranging from 0.5 to 28 μs. Finally, our data suggest that the 8‐μs criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M‐components. However, mixed‐mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28 μs, as observed in this study.

2018

An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Säntis Tower

Mohammad Azadifar, Lixia He, Davide Pavanello, Marcos Rubinstein

2018