Assessing currents of upward lightning measured in tropical regions

Guimarães, Miguel; Araujo, Listz; Pereira, Cláubia; Mesquita, Claudia R.; Visacro, Silvério

doi:10.1016/j.atmosres.2014.01.005

Cited by 21 publications

(8 citation statements)

References 12 publications

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“…Figure a refers to a negative CG lightning over a time interval that includes the positive UCL initiation and the attachment. Figures b and c refer to a negative upward lightning triggered by a nearby event, as all other upward lightning measured at MCS (Guimaraes et al, ). Note that both events include similar electric‐field profiles that indicate the effect of approaching negative leaders.…”

Section: Experimental Datamentioning

confidence: 96%

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

2017

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Original simultaneous records of currents, close electric field, and high‐speed videos of natural negative cloud‐to‐ground lightning striking the tower of Morro do Cachimbo Station are used to reveal typical features of upward positive leaders before the attachment, including their initiation and mode of propagation. According to the results, upward positive leaders initiate some hundreds of microseconds prior to the return stroke, while a continuous uprising current of about 4 A and superimposed pulses of a few tens amperes flow along the tower. Upon leader initiation, the electric field measured 50 m away from the tower at ground level is about 60 kV/m. The corresponding average field roughly estimated 0.5 m above the tower top is higher than 0.55 MV/m. As in laboratory experiments, the common propagation mode of upward positive leaders is developing continuously, without steps, from their initiation. Unlike downward negative leaders, upward positive leaders typically do not branch off, though they can bifurcate under the effect of a downward negative leader's secondary branch approaching their lateral surface. The upward positive leader's estimated average two‐dimensional propagation speed, in the range of 0.06 × 106 to 0.16 × 106 m/s, has the same order of magnitude as that of downward negative leaders. Apparently, the speed tends to increase just before attachment.

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Section: Experimental Datamentioning

confidence: 96%

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

2017

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“…It has been clear that upward flashes can occur with or without preceding lightning discharges, called “other‐triggered” and “self‐initiated” upward flashes, respectively (e.g., Wang et al, 2008). Numerous studies have been contributed to the triggering mechanism of upward negative flashes (Guimarães et al, 2014; Jiang et al, 2014; Pineda et al, 2019; Qi et al, 2018; Saba et al, 2016; Sunjerga et al, 2020; Takagi et al, 2006; Wang et al, 2008; Wang & Takagi, 2012a; Warner, 2012; Warner et al, 2012; Warner et al, 2014; Wu, Lyu, et al, 2019; Yuan et al, 2017; Zhou et al, 2012b; Zhu et al, 2019). One interesting phenomenon is that the ratio between other‐triggered and self‐initiated upward negative flashes varies significantly in different studies (e.g., Saba et al, 2016; Warner et al, 2012; Warner et al, 2014; Zhou et al, 2012b).…”

Section: Introductionmentioning

confidence: 99%

Upward Negative Leaders in Positive Upward Lightning in Winter: Propagation Velocities, Electric Field Change Waveforms, and Triggering Mechanism

Wang

Takagi

2020

JGR Atmospheres

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Upward negative leaders (UNLs) in positive upward lightning are rarely observed. In this study, 24 UNLs observed by the Fast Antenna Lightning Mapping Array during winter thunderstorms in Japan are analyzed. Three‐dimensional velocities of UNLs are calculated, and it is found that velocities during the upward propagation stage range from 1.8 to 27.9 × 105 m/s with a mean value of 10.4 × 105 m/s, and they are always larger than velocities during the following horizontal propagation stage. UNLs produce distinctive electric field change waveforms with V‐shaped overall change trend, with small pulses at the beginning when UNLs start, large pulses during upward propagations, and small pulses again when UNLs turn into horizontal directions. Pulses produced by UNLs are mainly unipolar but sometimes also bipolar. Pulse interval, pulse width, rise time, and fall time are calculated for waveforms produced by five UNLs. Pulse intervals range from 13.7 to 18.9 μs. Pulse width, rise time, and fall time are on average 5.8, 3.3, and 2.4 μs, respectively. All UNLs are preceded by other discharges. Strong negative strokes including some special types of strokes usually precede initiations of UNLs by tens of milliseconds. These negative strokes are usually found only a few kilometers away from UNLs. It is speculated that these negative strokes along with following in‐cloud positive leaders contribute to the depletion of negative charges in thunderclouds, which result in positive electric field changes (atmospheric electricity sign convention) large enough for initiations of UNLs.

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“…By replacing the triggering wire with a grounded tall structure, the phenomenology of rocket‐triggered lightning is similar to the natural upward lightning (Miki et al, ; Rakov et al, ). Upward flashes can be divided into two types ( self‐initiated and nearby‐lightning‐triggered type, Wang et al, ), but the initial current pulses and its associated E field changes are only observed in the upward flash of nearby lightning‐triggered type (Guimaraes et al, ; Visacro et al, ), which suggests that these current pulses are attributed to the approach of horizontally propagating negative part of bipolar leaders in the cloud. In contrast, the initial current pulses are commonly observed in rocket‐triggered lightning, but there is no observation of very high frequency (VHF) radiation related to downward negative leaders by lightning mapping array or broadband VHF interferometer, even though the negative leaders emitted strongly at VHF (Hill et al, ; Sun et al, ; Zhang et al, ).…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Electromagnetic Signals During the Initial Stage of Negative Rocket‐Triggered Lightning

Fan

Jiang

et al. 2018

JGR Atmospheres

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With the measurements in SHandong Triggering Lightning Experiment and GuangdongComprehensive Observation Experiment on Lightning Discharge in China, we examine the electromagnetic signals associated with the upward positive leaders during the initial stage of negative triggered lightning. The magnetic field (B field) signals measured at close range (<100 m) for both sites can be divided into two categories (i.e., impulsive and ripple pulses) according to the discernibility of separation between individual pulses. The impulsive pulses are well simulated by using the transmission line model, which suggests that these pulses are generated by leader current pulses propagating downward along the steel wire. Because the length of extended leader channel ahead of the wire is not negligible during the stage of ripple pulses, the waveform of impulsive current pulses is changed after traveling through the high impedance leader channel. Taking the filtered current pulse as the input variable, the waveform of ripple pulse can be simulated properly, which indicates that ripple pulses are caused by the attenuation of impulsive current along prolonging leader channel. In addition, the paper analyzes the fast electric field (E field) changes measured at 60-m range from the launching site during the initial stage by using the transmission line model and shows that the polarity of E field change at a given range is determined by the inception height of upward leader, namely the surface E field change caused by the individual charge transfer of initial upward leader also involves the problem of reverse distance as present for a vertical dipole. Plain Language SummaryLightning can occur at a predictable time and place by using the technique of rocket-triggered lightning, which launches a small rocket trailing a grounded steel wire toward the charged thundercloud overhead. Therefore, the technique facilitates the research of lightning discharges and their electromagnetic effects. At the beginning of triggered lightning, a sustained train of current pulses can be measured at the base of discharge path, and the synchronous electromagnetic field signals can also be recorded by the electric and magnetic sensors deployed around the rocket launching site. The paper focuses on the characteristics of electromagnetic signals measured at close range (<100 m) during the SHandong Triggering Lightning Experiment and Guangdong Comprehensive Observation Experiment on Lightning Discharge (two experimental sites of triggered lightning in China) campaign. The main contributions of this article include two aspects: first, we clarify the relationship between the electromagnetic signals and current pulses during the initial stage of triggered lightning; second, we demonstrate the influences of the triggering height on the polarity of electric field waveform.

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Assessing currents of upward lightning measured in tropical regions

Cited by 21 publications

References 12 publications

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

Upward Negative Leaders in Positive Upward Lightning in Winter: Propagation Velocities, Electric Field Change Waveforms, and Triggering Mechanism

Characteristics of Electromagnetic Signals During the Initial Stage of Negative Rocket‐Triggered Lightning

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