It is for the first time that the researchers have measured electric fields within thunderclouds. They used cosmic rays as suitable probes and the LOFAR radio telescope located in the Netherlands.

Researchers, who led the study at Radboud University in Nijmegen, have thrown some more light on how lightning is initiated in thunderclouds. How do you measure electric fields inside large, dangerously charged clouds, are the two questions that are very difficult to answer.

They said it was discovered, more or less by coincidence, that cosmic rays provide appropriate probes for measuring electric fields within thunderclouds.
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Schellart said, “We modeled how the electric field in thunderstorms can explain the different measurements. This worked very well. How the radio emission changes gives us a lot of information about the electric fields in thunderstorms”. He mentioned that they could even determine the strength of the electric field at a certain height in the cloud.

He said this field could be as strong as 50 kV/m. This gets translated into a voltage of hundreds of millions of volts over a distance of multiple kilometers. A thundercloud has enormous amounts of energy.

Astronomer Pim Schellart said they used to discard LOFAR measurements taken during thunderstorms, which were too messy. They never used to analyze them.

Schellart was interested in cosmic rays. These high-energy particles originate from exploding stars and other astrophysical sources. They continuously bombard Earth from space. High in the atmosphere, these particles strike atmospheric molecules and cause ‘showers’ of elementary particles.

The radio emission can also be used in measuring these showers. The emission is generated when their constituent particles are deflected by the magnetic field of the Earth. The radio emission also provides information about the original particles.

ASTRON in Dwingeloo conducts such measurements routinely with LOFAR, but not during thunderstorm.