- The Gamma Ray Astronomy PeV EnergieS phase-3 experiment is located at TIFR’s Cosmic Ray Laboratory in Ooty in Tamil Nadu.
- It is a collaboration of the Indian Tata Institute of Fundamental Research, the Japanese Osaka City University and the Japanese Nagoya Women’s University.
- GRAPES-3 (Gamma Ray Astronomy PeV EnergieS phase-3) is designed to study cosmic rays with an array of air shower detectors and a large area muon detector.
- It aims to probe acceleration of cosmic rays in the four astrophysical settings.
- The experiment had earlier detected the effect of a solar storm that hit the earth in June 2015.
- The muon telescope has been successfully used to study acceleration of muons during large thunderstorm events.
- GRAPES-3 also has an important role in understanding the propagation of storms from the L1 point (Lagrange point) to its impact on the Earth.
Note: Lagrange Points are positions in space where the gravitational forces of a two body system like the Sun and the Earth produce enhanced regions of attraction and repulsion.
How potential of thundercloud was measured using GRAPES-3?
- Clouds have negative charges along their lower side and positive charges on top and can be several kilometres thick. However, thunderstorms last only for about 15-20 minutes, which makes it difficult to calculate the potential of thundercloud.
- Muons and other particles are produced when cosmic rays bombard air particles surrounding the earth.
- The muons produced can have positive or negative charge.
- When a positively charged muon falls through a cloud, it loses energy. If its energy falls below 1 giga electron volt (GeV), which is the threshold of detection of the GRAPES-3 muon telescope, it goes undetected.
- When a negatively charged muon falls through a cloud, it gains energy and gets detected.
- Since there are more positive than negative muons produced in nature, the two effects don’t cancel out, and a net change in intensity is detected.
- The researchers monitored the profiles of the clouds using four ground-based electric field monitors.
- Only the cloud that crossed on December 1, 2014, had a profile that was simple enough to simulate.
- Using a computer simulation and the observed muon intensity variations, the researchers worked out the relationship with the electric potential of the cloud.
- They calculated that the potential of the cloud they were studying was approximately 1.3 GV, which no one has ever measured potential, size and height of a thundercloud simultaneously.
- This method in future can be used to understand the terrestrial gamma ray bursts (huge flashes of light that accompany lightnings).
- Learning about the properties of thunderclouds can be useful in navigation of aircraft and preventing short circuits. This serendipitous discovery might provide the means to making headway in this direction.