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Focus: Muons show record breaking thunderstorm tension

& bullet; Physics 12, 29

A thunderstorm studied with atmospheric muons had an electrical potential of more than one billion volts, well above the previously measured values.

A shock. Using a muon detector, the researchers measured a record-breaking electrical potential of more than 1 billion volts.

Researchers have documented a thunderstorm that generates an electrical potential of about 1.3 billion volts (GV), ten times greater than the largest value ever reported. The new method of monitoring the storm thunderstorms uses the muons that rain down on Earth with cosmic rays that strike the atmosphere. The potential of a storm cloud can reduce the charged particle energy and reduce the likelihood that it will be discovered under the storm. The new measurement shows that thunderstorms with potentials of several billion volts are possible, voltages high enough to account for the mysterious flashes of high-energy gamma rays sometimes seen in thunderstorms.

Since Benjamin Franklin flew a kite on a stormy afternoon in 1752. We have known that thunderstorms involve electrical phenomena – lightning and thunder are the manifestations of sudden discharges between charged areas of the atmosphere. To study the electrical structure of storm clouds, researchers send planes or balloons to the storm centers. In these tests, electrical potentials of several tens of millions of volts were found, with the greatest value in a mountain storm in New Mexico in the nineties was at 130 megavolt [1]. However, airplanes and balloons can only survey the small region of the storm through which they fly and can not measure the potential across the entire cloud.

The method developed by Sunil Gupta of the Tata Institute of Fundamental Research in Mumbai, India. and colleagues is based on studying the effect of thunderstorms on the detection of particles by G3MT, a muon telescope in southern India (part of the GRAPES-3 Cosmic Radiation Detector). The telescope detects muons produced by cosmic radiation in the atmosphere – charged particles that mainly come from outside the solar system. Researchers at several other muon telescopes have previously observed thunderstorms that correlated with changes in the measured number of muons (of the river). Now, the Gupta team has taken the next step and developed a quantitative method. "We recognize that GRAPES-3 is an ideal tool for measuring thunderstorm potential, especially during the biggest storms," ​​says Gupta.

The majority of muons detected by G3MT are positively charged antimonic agents that normally lose energy when responding to the complicated arrangement of thunderstorm cloud charges. At reduced energies, the muons are less likely to be picked up by the detector, which measures only particles with energies above a certain threshold. The storm is therefore registered as a reduction in the detected muon flux, which can be up to a few percent. With over one million muons reaching G3MT per minute, the system can measure the muon flux changes to an accuracy of 0.1%. The telescope can also distinguish between 169 discrete directions.

Flow measurements enable Gupta and his colleagues to estimate the storm potential using computer simulations based on a simplified description of the thunderstorm. They treat it as a huge condenser consisting of two parallel plates spaced 2 km apart, producing an upward electric field.

Between 2011 and 2014, researchers collected data on 184 thunderstorms, citing the seven biggest events. However, six of them had a complex time profile, making it difficult to calculate the potential. The researchers focused on the seventh storm, which took place on December 1, 2014, and identified an electrical potential with record highs of 1.3 GV.

"This muon-based technique provides a unique, albeit indirect way to investigate the electrical fields in the Earth's largest natural particle accelerators – lightning and thunderstorms," ​​says Michael Cherry, of Louisiana State University at Baton Rouge The analysis relies on Monte Carlo simulations and simplifying assumptions that may not apply to all storms, he says, but the derived value shows much greater potential than previously measured with balloons suggests that launching a balloon or a drone during a thunderstorm while observing muons could provide a test for one of the most important model parameters: the distance of 2 km between the plates of the condenser, which orients itself to the thunder cloud.

The new finding may also be helpful to researchers An atmospheric puzzle, says Gupta. Since 1994, satellite measurements have produced gamma-ray flashes several tens of kilometers in height. The researchers suspect that these flashes could be produced by thunder-accelerated electrons, but early measurements did not find enough storm-light potential. However, the newly observed potentials in the gigavolt range are much closer to the values ​​required to produce the observed gamma rays. Gupta's team is now setting up gamma ray detectors near GRAPES-3, hoping to provide conclusive evidence by capturing gamma-ray bursts along with a Gigavolt-level thunderstorm.

This study was published in Physical Review Letters . .

– Matteo Rini

Matteo Rini is the Deputy Editor of Physics.


  1. T. Marshall and M. Stolzenburg, "Tensions Within and Just Above Thunderstorms", J. Geophys Res.: Atmos 106 4757 (2001).


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