The sky is very dark. Suddenly, comes a flash of light! Then you hear a loud sound, ‘crack-boom-ba-boom-boom!’ Well, that’s a thunderstorm. A thunderstorm is a common occurrence all around the world and has been witnessed by man since time immemorial. It is defined as a momentary weather perturbation that is associated with thunder, lightning, rain clouds, heavy rain or hail, and violent winds. So, what causes a thunderstorm?

Formation of a Thunderstorm

Thunderstorms occur when warm and humid air rises upwards towards the cooler areas of the atmosphere with large volumes and increasing velocity, initiating an updraft. The moisture contained in the updraft condenses to form cumulonimbus clouds, leading to precipitation. A stream of cool air then moves towards the earth and hits the ground with strong downdrafts and horizontal winds. Simultaneously, electrical charges get collected on cloud particles. Upon heavy accumulation of electric charge, lightning discharges occur, which heats the air it passes through, creating shock waves. These shock waves are eventually heard as rambles and cracks of thunder.

Recent Finding

According to a recent study, it was found that thunderstorms may store up much higher electric voltages. By using muons, heavier relatives of electrons that continuously pour down on the surface of the earth, researchers explored the interior of a storm in the southern part of India in December 2014. They found that the electric potential of the cloud, which is defined as the work required to move an electron from one part of the cloud to another, reached 1.3 billion volts, which amounts to 10 times the largest voltage discovered earlier by using balloons to make similar measurements. The study was reported in the peer-reviewed scientific journal, ‘Physical Review Letters.’

It can be difficult to monitor a cloud using a balloon and aircraft to get an accurate measurement of the whole thing, as they can monitor only a part of a cloud. However, with muons, the monitoring becomes a smooth ride as they zip right through the cloud. According to Sunil Gupta, a physicist from the Tata Institute of Fundamental Research in Mumbai, India, muons entering the thundercloud are a perfect mode to measure the electric potential. His team studied the nature of muons with the GRAPES-3 experiment located at Ooty in India. The experiment aims to probe cosmic rays with an array of air shower detectors and a large area muon detector. It observes nearly 2.5 million muons every minute. When thunderstorms take place, that number comes down as muons are electrically charged and gets slowed by a thunderstorm’s electric fields.

By applying computer simulations of a thunderstorm, the scientists figured out the electric potential needed to explain the drop in muons witnessed during the 2014 event. The team also found that the storm’s electric power matched with the output of a large nuclear reactor, at around 2 billion watts.

Upon confirmation, such high voltages inside a thunderstorm could explain that storms send bursts of high-energy upward. However, scientists are unable to understand the processes that could generate such a powerful light.