Unusually high ozone found over Bay of Bengal: Scientists unravel the mystery

Scientists have detected an unusually thick layer of ozone high above the North Bay of Bengal, the Ministry of Science & Technology said on Monday. The layer formed about 21 to 23 km above the Earth's surface and remained there for more than a day.

The discovery has helped researchers understand how ozone-rich air is transported through the atmosphere.

The findings, published in Earth and Space Science by the American Geophysical Union, provide experimental evidence of how stratospheric ozone is redistributed over India's subtropical region during winter.

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WHAT DID SCIENTISTS FIND?

The ozone layer normally reaches its highest concentration at an altitude of around 25 to 30 km.

But during the Phase-I NetRAD-ASMA campaign, scientists found an unusually thick ozone layer at a lower altitude of 21 to 23 km over the North Bay of Bengal.

The amount of ozone was much higher than normally observed over eastern India. The layer also persisted for more than a day.

That raised a key question: How did so much ozone accumulate at that altitude?

HOW DID THEY SOLVE THE MYSTERY?

Scientists brought together data from several sources.

These included atmospheric radars, weather balloons, satellites and advanced atmospheric models. The study involved researchers from institutions across India, including the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology.

During the campaign, the indigenously developed 206.5 MHz Stratosphere-Troposphere Radar at ARIES, Nainital, collected data along with similar radars at Haringhata, Gadanki and Kochi.

Researchers also launched weather balloons equipped to measure atmospheric conditions and ozone levels.

Satellite observations from Aura MLS and INSAT-3DR provided additional evidence of the unusual ozone structure.

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WHY DID THE OZONE BUILD UP?

The researchers initially examined whether sunlight-driven chemical reactions could have caused the increase.

But the enhanced ozone layer was observed during both daytime and nighttime. This suggested that photochemical processes were unlikely to be the main cause.

Scientists then looked at convection, wind shear, horizontal transport and vertical air movement.

Their observations showed persistent downward movement of air in the lower stratosphere.

By combining the different sets of evidence, researchers concluded that the unusual ozone enhancement was mainly caused by ozone-rich air being transported into the region, followed by downward movement and compression of the air mass.

WHY DOES THIS MATTER?

Ozone in the stratosphere is important because it absorbs harmful ultraviolet radiation from the Sun and helps protect life on Earth.

The study also shows why coordinated atmospheric observations are important for understanding how ozone moves over the Indian region.

The research was conducted under the Phase-I NetRAD-ASMA campaign, a nationwide programme involving several Indian research institutions. Among the researchers were ARIES scientists Dr Manish Naja and Dr Samaresh Bhattacharjee.