Scientists have detected an unusually high concentration of ozone in the upper atmosphere over the North Bay of Bengal, providing new insights into how air currents transport and redistribute ozone in the stratosphere over the Indian region.
The unusual ozone layer was found at an altitude of around 21 to 23 kilometres above the North Bay of Bengal and remained in place for more than a day. Researchers said the concentration was significantly higher than normally observed over eastern India.
The findings, published in Earth and Space Science by the American Geophysical Union, provide quantitative experimental evidence of the redistribution of stratospheric ozone over the Indian subtropical region during winter.
The study was conducted as part of the Phase-I NetRAD-ASMA campaign, a nationwide scientific programme that brought together research institutions to investigate atmospheric processes and improve understanding of the Earth’s atmosphere.
Scientists from several Indian institutions participated in the campaign, including researchers from the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology. ARIES scientists Dr Manish Naja and Dr Samaresh Bhattacharjee were among those involved in the study.
Researchers used observations from a nationwide network of atmospheric radars, weather balloons and satellites, along with advanced atmospheric models, to investigate the unusual ozone enhancement.
The indigenously developed 206.5 MHz Stratosphere-Troposphere Radar at ARIES in Nainital collected data alongside similar radars located at Haringhata, Gadanki and Kochi. Weather balloons equipped with instruments to measure atmospheric conditions and ozone concentrations were also launched during the campaign.
The simultaneous observations from different parts of India enabled scientists to compare wind patterns and vertical air movements and examine the atmospheric conditions associated with the unusual ozone event.
The ozone layer normally reaches its maximum concentration at an altitude of about 25 to 30 kilometres and plays a crucial role in protecting life on Earth by absorbing harmful ultraviolet radiation from the Sun.
Scientists initially faced the question of why such a large amount of ozone had accumulated at a relatively lower altitude over the North Bay of Bengal.
To investigate the phenomenon, the researchers combined ozone and meteorological measurements from balloons with data from the national radar network, the Aura Microwave Limb Sounder (MLS) satellite and INSAT-3DR, along with atmospheric modelling.
The enhanced ozone layer was detected during both daytime and nighttime. This indicated that sunlight-driven photochemical processes were unlikely to have been the main reason for the unusual increase.
Satellite observations independently confirmed the unusual ozone structure recorded by the balloon measurements.
The researchers examined several atmospheric processes, including convection, wind shear, horizontal transport and vertical air movement. The observations revealed persistent downward air motion in the lower stratosphere over the region.
By combining evidence from the different observational systems, scientists concluded that the unusual ozone enhancement was primarily caused by the transport of ozone-rich air, followed by downward movement and compression of the air mass.
The study offers a clearer picture of how atmospheric circulation can redistribute ozone over the Indian subtropical region during winter and provides valuable data for understanding stratospheric dynamics.
Scientists said the findings also demonstrate the importance of coordinated atmospheric observations across the country. The study highlights the role of indigenous scientific infrastructure, particularly the ARIES Stratosphere-Troposphere Radar and balloon-based measurements, in advancing research on atmospheric processes.
