Measuring lightning for a better knowledge of thunderstorms

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Did you know?
In June 2020, two world records for the length and duration of a single flash ("mega-flashes") were officially approved by the World Meteorological Organization. Established thanks to new lightning satellite imaging techniques, these two records are more than twice as important as those previously recorded in the USA and France.

What are the longest flashes?

These extremes, also known as “mega-flashes”, can reach several hundred kilometres and last several seconds.1.
  • On 31 October 2018, a single lightning flash of 709 ± 8 km (440,6 ± 5 miles) was recorded in southern Brazil. This is the longest length ever recorded in the world for a single flash of lightning. This is equivalent to the distance between Boston and Washington in the United States, or between London and the Swiss border near Basel;
  • On 4 March 2019, a flash of 16.73 seconds was detected in the north of Argentina. This is the longest duration ever observed for a single flash.

These two records replace those already approved in 2016. :
  • 321 kms in Oklahoma, USA, observed in 2007
  • 7.74 seconds in the South of France in 2012

Who makes these observations and on which detection technology are they based?

While recent records have been established thanks to satellite remote sensing, the measurement of the 2012 record in France had already been the subject of a unique observation.

Then led by Hymex, a multidisciplinary scientific project on an international scale led by Météo France and the CNRS, its study aimed to analyse the hydrological cycle of the Mediterranean basin on a long-term plan. In order to carry out these observations, a specific campaign was conducted (SOP1) thanks to the deployment of several lightning observation and measurement systems.

Parmi eux, le HyLMA, based on technology using a ground-based Lightning Mapping Array networks of atmospheric electricity and precisely measuring the details of lightning propagation in 3D. This network is made up of 12 sensors some 30 km apart and covering a 250 km zone around Alès (France)
It has made it possible to detect and locate as closely as possible, continuously and in real time, the "ionised channels" (also called leaders) in the clouds and the surrounding atmosphere that make the air conductive and lead to the creation of the electrical discharges that cause lightning.

These records are officially validated by the World Meteorological Organization (WMO) Committee on Extremes of Weather and Climate,in charge of the official record of extremes at the global, hemispheric and regional scales.
This committee is composed of many international experts, recognised worldwide for their experience and scientific contribution on the subject.
Within this committee, France is represented by Stéphane Pedeboy, Technical Director of Météorage and member of the "ST Lightning" scientific team of the Hymex project.
Record 2012 - Hymex
Figure 1 - Hymex project: The record lightning flash registered in the night of 30 August 2012 (7.74 sec) covered a distance of about 160 km and an area bounded by a pentagon with peaks in Mirabel, Uzès, Pourrières, Mézel and Lesches-en-Diois.

In general, how many seconds does a flash last?

The duration of most lightning flashes generally does not exceed a few hundred milliseconds. However, in order for such an exceptional phenomenon, such as one of these records, to be observed, certain extreme conditions must occur and come together.

What can we learn from these measures?

Firstly, the studies carried out by the Hymex project highlighted the unusual character of the electrical structure of the cloud when the lightning flash occurred.
Secondly, the observations made possible to establish the observation that the processes and mechanisms at the origin of the electrification of the storm cloud are not yet fully understood.2

The detailed study of lightning contributes to the research work carried out for decades by the scientific community to better understand thunderstorms and to evolve the definitions and standards established by the WMO on lightning.
However, the measurement of these different records does not necessarily reflect more extreme phenomena, but rather the continuous progress made in the field of remote sensing of thunderstorms on a global scale.

To identify these “mega-flashes”, specialists have continued their research since the observations validated in 2016: thanks to space-based lightning mapping, it has been possible to continuously measure the length and duration of lightning flashes over larger geospatial areas using instruments installed on board observation satellites.
Even more extreme values are probably yet to be discovered and it will certainly be possible to observe them when lightning detection techniques become even more advanced.

These new records illustrate that the dangerous nature of thunderstorms can occur over a particularly long distance. These results are important for “safety, engineering and scientific issues” and highlight public safety concerns, which are reconsidered when such phenomena occur.

1 Read ici the official press release of the records validation.
2 Consultez ici l’intégralité des résultats du projet Hymex

Marie Candau
File written by Marie C. She is our expert in interviews and testimonials
As an interlocutor of the press in Europe, her experience of almost 10 years encourages her to ask the right questions but also to answer those that her interlocutors naturally ask themselves…

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