Historical research guide · 0487 · 2018
Assessment of ball lightning cases by correlated LLS data
Alexander G. Keul · Gerhard Diendorfer
In one minute
Ball lightning has almost no instrument record. It arrives without warning, lasts seconds, and is gone before anything can be pointed at it. Alexander Keul and Gerhard Diendorfer found a way to put an instrument behind the eyewitness after the fact. Europe is blanketed by EUCLID, a lightning-detection network that logs every stroke’s position, time, polarity and peak current. Take a ball lightning report with a known place and time, open the network’s records for that spot and that minute, and see what ordinary lightning was doing. They did it for thirty-four cases from Germany, Austria, the Czech Republic and Switzerland between 1994 and 2016. Nineteen of the matched strokes were positive and fifteen negative; the positive ones ran from four to three hundred and seventy kiloamperes. The pattern is the interesting part — the larger the peak current, the closer the ball appeared to the stroke. That is what a real trigger should look like, and it is the first statistical handle on the moment these objects are born.
Connection
Chapter 9 needs ball lightning treated as an instrumented phenomenon rather than a story, and this is the paper that first attaches an existing continental measurement network to the case record. Chapter 1 gets a clean rung on its ladder from it: the authors state exactly what the network can and cannot deliver, and end with the replication that would confirm the pattern — which they then ran.
From the source
Thirty-four ball lightning case reports from the period 1994 to 2016 were matched against EUCLID lightning-location records — nineteen from Germany, ten from Austria, three from the Czech Republic and two from Switzerland. Twenty-eight occurred in the summer months and six in winter, and their time-of-day pattern follows the diurnal thunderstorm frequency of Central Europe. The seasonal and daily pattern of the reports is the pattern of thunderstorms themselves.Abstract, ICLP 2018, sentences on case distribution
Of the correlated EUCLID strokes, nineteen were positive and fifteen negative. The positive strokes ranged from four to three hundred and seventy kiloamperes, the negative from minus three to minus thirty-seven kiloamperes. Twenty-eight were classified by the network as cloud-to-ground and six as intra-cloud. Positive polarity in a majority of matches is notable in itself, because positive strokes are the minority of ordinary lightning.Abstract, ICLP 2018, sentences on polarity and peak current
For the close events — those with the ball reported less than one kilometre from the located stroke — the mean stroke-to-ball distance was 0.42 kilometres with a range of zero to 0.8 kilometres. For the distant events, one to ten kilometres, the mean was 5.7 kilometres with a range of 1.4 to ten. The network’s own positional uncertainty is stated alongside: the mean semi-major axis of the EUCLID location confidence ellipse was 0.45 kilometres, which is the same size as the close-event distances themselves.Abstract, ICLP 2018, sentences on distance statistics and the confidence ellipse
The load-bearing result is a correlation: across this sample, higher peak currents go with smaller ball-to-stroke distances, for both negative and positive cloud-to-ground events. The authors read that as a physical link between the stroke of maximum peak current and the ball lightning process that follows it, and as a reason to treat the distant matches as unlikely triggers, since a stroke’s physical effects at several kilometres are marginal.Abstract, ICLP 2018, closing three sentences
The method is stated with its own limits attached. The working idea is the initial flash hypothesis — that the electromagnetic pulse of a detected stroke near the reported position could be the triggering event. A lightning location system supplies stroke position, time, polarity and peak current, and no more: the authors state plainly that no electromagnetic field values for individual strokes can be computed from a peak current in kiloamperes, and that intra-cloud strokes have no defined striking point, so the distance derived for those six cases is a different quantity from the twenty-eight cloud-to-ground ones.Abstract, ICLP 2018, method sentences
What to watch: the paper ends by saying that replications with more cases will show whether the pattern holds — and the same authors ran it. Keul, Pichler and Diendorfer reported a follow-up at the 2024 conference with fifty-eight European cases from 1993 to 2023, searching the records sixty minutes either side of each report within a ten-kilometre radius. Fifty-three per cent of determinable distances came in under one kilometre, eighty-three per cent of the negative trigger strokes were under minus thirty kiloamperes, and seventy-one per cent of the positive ones were over fifty kiloamperes, with forty-three per cent over one hundred. Thirty-five per cent of the triggers were isolated strokes.Abstract, ICLP 2018, final sentence; ALDIS entry for Keul, Pichler and Diendorfer, ICLP 2024
The way in
https://doi.org/10.1109/iclp.2018.8503422How to cite it
Alexander G. Keul, Gerhard Diendorfer (2018) Assessment of ball lightning cases by correlated LLS data doi:10.1109/iclp.2018.8503422