An analysis of the charge structure of lightning discharges to ground

Abstract

Sources of charge for the individual strokes of four multiple‐stroke flashes to ground have been determined, using measurements of the electrostatic field change obtained at eight locations on the ground beneath the storm. The resulting charge locations have been compared to 3‐cm radar measurements of precipitation structure in the storm. The field changes of individual strokes were found to be reasonably consistent with the lowering to ground of a localized or spherically symmetric charge in the cloud. The centers of charge for successive strokes of each flash developed over large horizontal distances within the cloud, up to 8 km, at more or less constant elevation between the −9° and −17°C environmental (clear air) temperature levels. Comparison with the radar measurements has shown that the discharges developed through the full horizontal extent of the precipitating region of the storm and appeared to be bounded within this extent. In one instance where cellular structure of the storm was apparent, the strokes selectively discharged regions where the precipitation echo was the strongest. Vertical extent of the stroke charge locations was small in comparison with the vertical extent of the storm. The field changes in the intervals between strokes have been found to exhibit many of the features which Malan and Schonland used to infer that ground flashes discharge a nearly vertical column of charge in the cloud. This and other evidence is used to show that their observations, which were made at a single station, could instead have been of horizontally developing discharges. The interstroke field changes have been analyzed using a point dipole model and found to correspond to predominantly horizontal charge motion that was closely associated with the ground stroke sources for the flashes. The interstroke activity served effectively to transport negative charge in the direction of earlier stroke volumes and often persisted in the vicinity of an earlier stroke volume, while subsequent strokes discharged more distant regions of the cloud. Long‐duration field changes that sometimes preceded the first stroke of a flash have been analyzed and found to correspond to a series of vertical and horizontal breakdown events within the cloud, prior to development of a leader to ground. These events were associated in part with the negative charge region that became the source of the first stroke and effectively transported negative charge away from the first stroke charge volume and from the charge volumes of subsequent strokes. Several continuing current discharges were found also to progress horizontally within the cloud and sustained currents in the range of 580 A to less than 50 A. The continuing current field changes were consistently better fitted by the monopole charge model than the field changes of discrete strokes within the same flash.

Measurement of charge transfer in sprite‐producing lightning using ELF radio atmospherics

“…Previous measurements of charge transfer in lightning return strokes have been made by directly measuring current when lightning strikes an instrument tower [Berger, 1967] or an electrically-grounded rocket [Hubert et al, 1984], and from multi-site electrostatic field measurements [Krehbiel et al, 1979]. The difficulty in these measurements is a matter of practical placement of the sensors: direct rocket or tower observations must be made at the location of the lightning, and electric field observations must be made at most a few tens of Copyright 1997 by the American Geophysical Union.…”

Determination of Charge Structure of Multiple Cloud-to-Ground Flashes Based on Electric Field Recordings Obtained From the Local Lightning Detection Network in Warsaw During Summer of 2009.

“…[3] przedstawili po raz pierwszy metodę wykorzystania jednoczesnych rejestracji zmian pola elektrycznego (∆E) w czasie wyładowań atmosferycznych, z naziemnej i wielopunktowej (8 stacji) sieci pomiarowej, do wyznaczenia lokalizacji 3D źródła ładunku elektrycznego oraz jego wartości Q rozładowywanej przez poszczególne udary piorunowe wyładowań doziemnych. O ile do znalezienia jednoznacznego rozwiązania układu czterech równań z poszukiwanymi czterema niewiadomymi {x, y, z, Q} jest wystarczający zestaw czterech stacji pomiarowych, to ich nadmiar daje moŜliwość uzyskania większej wiarygodności (poziomu ufności) dla poszczególnych (poszukiwanych) rozwią-zań.…”

“…Analiza "post-time" zarejestrowanych danych piorunowych, uzyskanych z sześciu niezaleŜnych stacji pomiarowych sieci LSDWA w postaci odpowiadają-cych zmian natęŜenia pola elektrycznego ∆E i , została oparta na załoŜonym modelu ładunku punktowego dla źródła składowej wielokrotnego wyładowania doziemnego [1,3].…”

“…Wyniki symulacji lokalizacji źródeł wyładowań doziemnych dla losowych parametrów (x, y, z, Q) wykazały często, Ŝe lokalizacja tą metodą była nietrafiona. Podobny rezultat osiągnięto przy minimalizacji metodą Newtona [3]. Świadczy to o tym, Ŝe lokalne minima funkcji (2) nie zawsze pozwalają prawidłowo lokalizować źródła wyładowania doziemnego oraz Ŝe bardziej skuteczna powinna być tu metoda globalnej minimalizacji funkcji (2).…”

A multipole expansion method for analyzing lightning field changes

“…Ground4msed measmements of changes in the cloud electric field (AE) have been used for many years to estimate the location, magnitude, and polarity of lightning-caused changes in thundercloud charge dismbutions [e.g., •lson, 1920; Workman and Holzer, 1939; Jacobson and Krider, 1976; Krehbiel et al, 1979;Krehbiel, 1981Krehbiel, , 1986Maier and Krider, 1986;Krider, 1989, 1994;Murphy et al, 1996]. Recent analyses use least squares optimization proc•ures to describe the source.…”