On the cosmic ray trail in Tirunelveli

Equatorial Geophysical Research Laboratory has been monitoring the Earth’s near-space environment for over 25 years

When experimental activities at the centre first commenced in 1991, the geomagnetic equator passed right through the city.

“They installed these huge towers and we stopped getting rains,” says K. Vijayalakshmi, a resident of Krishnapuram village pointing at the MF Radar antennas (30 m tall towers) at the Equatorial Geophysical Research Laboratory (EGRL), Tirunelveli.

The four antenna towers that Vijayalakshmi pointed to, though creating a panic among the locals have nothing to do with rains. They are part of atmospheric radar that helps study the winds at heights between 70 km and 100 km above the Earth.

Located at a distance of 11 km from Tirunelveli, EGRL, spread over an area of more than 35 acres, is a regional centre of the Indian Institute of Geomagnetism (IIG), Mumbai. A multi-disciplinary centre with instruments to measure the Earth’s magnetic field variations and various atmospheric parameters, the facility has been continuously monitoring the Earth’s near-space environment for over 25 years now.

“Like the surface winds that we are familiar with, winds in the upper atmosphere too are highly variable. Understanding what causes those variable winds has been a primary focus of study at EGRL,” explains Dr. Sathishkumar, associate professor at the laboratory. “Lower atmospheric disturbances like severe weather events can have their signatures in the upper atmosphere, too. We are trying to establish the teleconnection between distant regions of the atmosphere and their impact on regions up to 100 km height and beyond.”

Why Tirunelveli?

Tirunelveli is in close proximity to both the geomagnetic and geographic equator. When experimental activities at the centre first commenced in 1991, the geomagnetic equator passed right through the city.

When winds blow, electric currents are expected to be produced in the electrically charged upper layers of the atmosphere across the geomagnetic field. Over Tirunelveli and the adjoining regions, where the geomagnetic field is horizontal the current flowing primarily in the east–west direction would be enhanced. Scientists call this current ‘Equatorial Electrojet’ and probing this helps scientists understand the Sun–Earth connection.

Secondary cosmic ray study

Another major experimental facility recently set up at EGRL is meant to monitor secondary cosmic rays. When the cosmic rays — from supernovae, colliding galaxies and spinning black holes — enter the Earth’s atmosphere, they lose their energies through collisions with our atmospheric molecules and produce a cascade of subatomic particles known as secondary cosmic rays.

“There is a significant anti-correlation between solar activity and the intensity of the cosmic rays. There is also a debate about whether secondary cosmic rays can trigger earthquakes and volcanic activity”, explains Dr. C.P. Anil Kumar, Head at EGRL.

Answers from Antarctica

Besides the magnetometer network in Indian landmass, IIG routinely operates magnetometers in the Indian stations in Antarctica, namely, Maitri and Bharati.

“The importance of monitoring the geomagnetic field over Antarctica is that it is the polar region where the magnetic fluxes are dense and where the Sun’s particle effects are first felt on Earth,” explains Mr. K. Jeeva, Technical Officer at EGRL.

Whenever the Sun’s activity becomes violent — for example, during a solar flare or during episodes of coronal mass ejections — the Earth’s magnetic field would readily encounter energetic particles.

“A chain of events takes place in the Earth’s electromagnetic environment following a solar event resulting in electrical currents at high altitudes and heating of the upper layers of the atmosphere over Antarctica. Such intense overhead currents are responsible for ground-induced currents that can create havoc for the underground telecommunication lines and electrical power grids,” explains Dr. Jeeva.

IIG also operates a suite of instruments at Antarctic stations to understand the impact of the disturbances on the Sun on the Earth’s environment.

Besides the traditional magnetometers, IIG also operates induction coil magnetometers to sense the extreme low-frequency signals produced by global thunderstorm/lightning activity. “Antarctic continent is free from local or regional lightning activity. The Indian Antarctic stations are thus ideal sites to monitor global fluctuations in lightning activity,” Dr. Jeeva adds.

Monitoring the electromagnetic signatures simultaneously from Indian continental landmass and the Antarctic enables the scientists to understand the hidden teleconnections between the polar and equatorial regions. Moreover, such studies throw light on space weather, a scientific and technological domain affecting the very many man-made satellites orbiting the Earth and the instruments on board used for a variety of purposes.