Scientists Find Unusual Ozone Layer Over North Bay of Bengal

esearchers found that the enhanced layer persisted during both daytime and nighttime, making sunlight-driven photochemical processes an unlikely primary explanation for the event.

Scientists have detected an unusually high concentration of ozone in the stratosphere over the North Bay of Bengal, giving researchers fresh evidence of how winds and vertical air movements can redistribute ozone high above the Indian region. The unexpected layer appeared at an altitude of around 21 to 23 kilometres, remained present for more than a day and contained considerably more ozone than researchers normally observe over eastern India.

The discovery emerged from a nationwide atmospheric research campaign involving institutions across India, including the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology. Researchers combined observations from atmospheric radars, weather balloons, satellites and advanced models to trace where the ozone-rich air came from and understand why it became concentrated at that particular altitude.

Ozone Concentration Found Below Its Usual Peak Altitude

Earth's ozone layer plays a crucial role in protecting life by absorbing harmful ultraviolet radiation from the Sun, with its highest concentrations generally found around 25 to 30 kilometres above the surface. The unusually thick layer detected over the North Bay of Bengal was located lower in the stratosphere, at roughly 21 to 23 kilometres, making its persistence and high ozone concentration particularly interesting to atmospheric scientists.

The observations were collected during the Phase-I NetRAD-ASMA campaign, a national scientific programme created to study complex atmospheric processes through coordinated measurements at multiple locations. Scientists including Dr Manish Naja and Dr Samaresh Bhattacharjee from ARIES participated in the research, whose findings have been published in the American Geophysical Union journal Earth and Space Science.

Indian Radars and Weather Balloons Track Unusual Ozone Event

A major part of the experiment involved the indigenously developed 206.5 MHz Stratosphere–Troposphere Radar at ARIES in Nainital, which gathered observations alongside similar radar facilities at Haringhata, Gadanki and Kochi. Weather balloons equipped with instruments for measuring atmospheric conditions and ozone levels were launched during the campaign, allowing researchers to study conditions at different heights rather than relying only on measurements from the ground.

Simultaneous observations from different regions gave the research team a wider view of wind patterns and vertical movements across India. Scientists combined these measurements with information from the Aura Microwave Limb Sounder and INSAT-3DR satellites, giving them independent observations of the unusual ozone structure and helping confirm what the balloon instruments had detected.

Downward Air Movement Linked to Ozone Build-Up

The biggest question was whether chemical production driven by sunlight had caused the elevated ozone levels. Researchers found that the enhanced layer persisted during both daytime and nighttime, making sunlight-driven photochemical processes an unlikely primary explanation for the event.

Attention then shifted towards atmospheric dynamics, including convection, wind shear, horizontal transport and vertical movement. Measurements showed persistent downward motion in the lower stratosphere, providing an important clue to how ozone-rich air could have reached the observed altitude and become concentrated there.

Evidence collected across the different instruments indicated that ozone-rich air had been transported into the region, followed by downward atmospheric movement and compression of the air mass. This combination emerged as the main explanation for the unusually high ozone concentration rather than ozone being produced locally through photochemical activity.

Nationwide Observations Offer New Insight Into Indian Stratosphere

The findings provide quantitative experimental evidence showing how atmospheric circulation can redistribute stratospheric ozone over India's subtropical region during winter. Understanding these movements is important because ozone concentrations at a particular location are shaped not only by atmospheric chemistry but also by winds that can move ozone-rich air horizontally and vertically over considerable distances.

The study also demonstrates how India's network of atmospheric research facilities can work together to capture events that would be difficult to understand using observations from a single location. Data from the indigenous ARIES Stratosphere–Troposphere Radar, balloon measurements, satellite observations and atmospheric models created a more complete picture of what happened above the North Bay of Bengal and why the unusual layer persisted.

Researchers expect coordinated atmospheric observations of this kind to improve scientific understanding of ozone distribution, stratospheric circulation and the processes shaping the atmosphere over India.