1.3 billion volts inside thunderstorms: A secret revealed by cosmic particles
Amman3 min read
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A recent scientific study has revealed that thunderstorms are not more frequent to the east of the Indian "GRAPES-3" telescope compared to the west, as previous measurements had shown; rather, the reason lies in the effect of the Earth's magnetic field on the cosmic particles that scientists use to monitor electrical activity inside clouds.
The study was published in the "Journal of Cosmology and Astroparticle Physics," and provided an explanation for the bias that has puzzled researchers for years, after the telescope recorded a much larger number of storms in the eastern part of its field of view.
Particles reveal electricity inside clouds
The "GRAPES-3" telescope is located in the city of Ooty in southern India, and its muon detector covers an area of about 560 square meters, monitoring nearly four billion muons daily. These particles are produced when cosmic rays coming from space collide with the Earth's atmosphere.
Muons are characterized by their ability to penetrate the atmosphere and reach the Earth's surface, making them an important tool for studying phenomena that occur inside thunderstorms.
Hariharan Balakrishnan, a researcher at the Tata Institute of Fundamental Research and the lead author of the study, explained that positive and negative muons are affected in opposite ways by the strong electric field inside clouds. Since the number of positive muons is greater than negative ones, their effects do not perfectly cancel out, leading to a change in the number of particles reaching the telescope.
By analyzing this change, scientists can estimate the electric potential difference inside storms without the need to send measuring devices directly into the clouds.
The team had previously used this method to estimate the potential difference in a thunderstorm at about 1.3 billion volts, a figure far exceeding the levels reached by direct measurements, which were estimated at about 130 million volts.
Why did storms appear more to the east?
The telescope monitored 487 thunderstorms during the period from April 2011 to December 2020. The data showed that 81.5% of the events were recorded in the east, compared to only 13.7% in the west.
However, comparing these results with independent measurements of the electric field in the atmosphere did not reveal a similar increase in thunderstorm activity in the east, which prompted researchers to look for a cause related to the observation mechanism itself.
Computer simulations showed that the Earth's magnetic field affects the paths of charged cosmic rays and changes the probabilities of their arrival in the atmosphere depending on their direction of movement. This is reflected in the numbers of positive and negative muons detected by the telescope.
The researchers found that the ratio of positive to negative muons is about 1.37 in the east, compared to 1.14 in the west, a difference that makes the telescope more sensitive to the electrical effect of storms located in the east.
When the team entered these ratios into the simulation, results similar to the actually recorded bias appeared, while the difference disappeared when the same ratio was used in both directions.
A new step for understanding storms
The results clarify that thunderstorms in the east do not necessarily possess a higher electric potential than those in the west, but rather their effect is easier to detect due to the difference in the numbers of muons reaching the telescope.
The researchers believe that solving this puzzle enhances the reliability of using muons to study electricity inside thunderclouds and opens the way for developing indirect means to measure the massive potential differences inside storms, relying on cosmic particles that constantly pass through the atmosphere.
