M‐component currents of first return strokes in natural negative cloud‐to‐ground lightning

Abstract

[1] Records of M-component currents of first return strokes in natural negative cloud-to-ground lightning measured in a short instrumented tower are shown along with correlated video records, electric field changes, and relative luminosity. The synchronized fast-camera records clearly match the increase of luminosity of the faint lightning channel. The parameters of these M components are all consistent with those of triggered lightning. According to records of electric field change of lightning events near Morro do Cachimbo Station and of currents measured at the instrumented tower, the frequency of first return strokes exhibiting M components is within the range of tens of percent and not of a few percent, as usually accepted. This expectation of a few percent is based on a very low number of first return strokes expected to be followed by continuing currents. It was found that most of the analyzed first-return-stroke M components of natural lightning occur at the final phase of the return-stroke process and not during the flow of continuing currents. Apparently, this also holds true for most of the first M components of subsequent return strokes.

An Advanced Model of Lightning M‐Component

“…In addition to M-components, Malan and Collens (1937) reported on "later components of branched strokes," which followed the return stroke and produced luminosity enhancements in the section of the grounded channel below the observable branching point. Since first stroke channels usually exhibit branches created by the stepped leader, some of the early M-components observed by Visacro et al (2013) are probably of the same nature as the branch components reported by Malan and Collens (1937).…”

“…For “early” M‐components, which immediately followed the first‐return stroke current peak, they reported a factor of 3 larger charge transfer to ground than that observed for M‐components in rocket‐triggered lightning by Thottappillil et al (). It is possible that M‐components reported by Visacro et al () were superimposed on the tail of return stroke current (as opposed to being superimposed on CC), which is expected to last up to 3 ms or so. In addition to M‐components, Malan and Collens () reported on “later components of branched strokes,” which followed the return stroke and produced luminosity enhancements in the section of the grounded channel below the observable branching point.…”

“…An example of electric field signature of in-cloud leader making connection with the continuing-current-carrying channel and producing a hook-shaped signature characteristic Since the occurrence of M-components requires the presence of CC, which is more likely to accompany subsequent return strokes (e.g., Rakov & Uman, 1990;Shindo & Uman, 1989), most of the information on M-components found in the literature corresponds to subsequent strokes. Visacro et al (2013) were the first who obtained current records of M-components in negative first strokes initiated by downward leaders terminated on the instrumented tower at the Morro do Cachimbo Station, Brazil. For "early" M-components, which immediately followed the first-return stroke current peak, they reported a factor of 3 larger charge transfer to ground than that observed for M-components in rocket-triggered lightning by Thottappillil et al (1995).…”

A New Engineering Model of Lightning M Component That Reproduces Its Electric Field Waveforms at Both Close and Far Distances

“…When measured at the channel base, the current pulses associated with the M component mode of charge transfer exhibit a more or less symmetrical waveshape (Fisher et al, 1993;Paul & Heidler, 2018;Thottappillil et al, 1995;Visacro et al, 2013) and they are responsible for the above mentioned transient enhancement in the channel luminosity (Campos et al, 2007;Flache et al, 2008;Jordan et al, 1995;Malan & Schonland, 1947;Qie et al, 2011;Stolzenburg et al, 2015;Winn et al, 2012;Zhou et al, 2014).…”

Correlation between the spectral features and electric field changes for natural lightning return stroke followed by continuing current with M‐components

“…And based on this conclusion, Campos et al [, ] investigated waveshapes of light signal during continuing current (CC) for negative and positive CG lightning from high‐speed video observation. Visacro et al [] showed that the profiles of current and relative light intensity were similar for M‐component of first return strokes. Recently, taking advantage of rocket‐triggered lightning, further works have been carried out on the current/light correlation.…”