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Scientists have detected an unusually thick layer of ozone about 21 to 23 kilometres above the North Bay of Bengal, with concentrations far higher than normally seen over eastern India and persisting for more than a day.
The study was carried out under the Phase-I NetRAD-ASMA campaign, a nationwide programme bringing together Indian research institutions; the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology, was an important participant.
The indigenously developed 206.5 MHz Stratosphere-Troposphere (ST) Radar at ARIES, Nainital collected data alongside similar radars at Haringhata, Gadanki and Kochi, supported by ozone- and weather-monitoring balloons, the Aura MLS and INSAT-3DR satellites and atmospheric models.
Because the enhanced layer appeared during both day and night, sunlight-driven photochemical processes were ruled out as the primary cause; observations showed persistent downward air motion in the lower stratosphere.
The researchers concluded the enhancement was mainly associated with transport of ozone-rich air, followed by downward atmospheric motion and compression of the air mass. The findings were published in Earth and Space Science of the American Geophysical Union.
The stratosphere extends from the tropopause up to roughly 50 km, and within it ozone is concentrated in a band usually peaking around 25-30 km — the ozone layer, which absorbs harmful ultraviolet radiation. Ozone is produced photochemically where sunlight is most intense, over the tropics, but the largest total column amounts are found over higher latitudes. The explanation is dynamical rather than chemical: the Brewer-Dobson circulation lifts tropical tropospheric air into the stratosphere, carries it poleward, and brings it back down at higher latitudes, redistributing ozone away from where it is made. That distinction between chemistry and dynamics is exactly what this study turns on. Because the enhanced layer over the Bay of Bengal was present at night as well as by day, photochemistry could not be the driver; the radars instead showed persistent downward air motion in the lower stratosphere. Sinking air is compressed, which concentrates the ozone already present in it — so an air mass that arrived rich in ozone from elsewhere became richer still on descending. Note also that the layer sat at 21-23 km, below the usual 25-30 km peak: the anomaly is as much about altitude as about amount.
Simple Analogy: Ozone is baked over the tropics but eaten at the poles, and the Brewer-Dobson circulation is the conveyor belt in between. Here the belt dipped, pressing a load of ozone-rich air downwards and squeezing it into a thinner, denser layer.
Autonomous research institute working in astronomy, astrophysics and atmospheric sciences; operates the indigenously developed 206.5 MHz Stratosphere-Troposphere Radar used in this study
The parent department under the Ministry of Science & Technology that funds and oversees ARIES and this class of coordinated national atmospheric campaigns
A ground-based radar that measures winds and vertical air motion through the troposphere and lower stratosphere — the instrument that revealed the persistent downward motion behind the ozone anomaly
The Microwave Limb Sounder aboard NASA's Aura satellite, which measures the vertical distribution of atmospheric constituents including ozone — used here to corroborate the balloon observations
India's meteorological satellite, used alongside Aura MLS to observe the unusual ozone structure
Downward transport of ozone-rich stratospheric air into the troposphere is a recognised natural contributor to surface ozone, which is why dynamical studies like this one matter for air quality modelling too
The 'ASMA' in the NetRAD-ASMA campaign name refers to the study of the atmospheric structure over the Asian monsoon region — a system that traps and transports pollutants and trace gases into the stratosphere and is a major focus of Indian atmospheric research
The 206.5 MHz ST Radar at ARIES and the Gadanki MST Radar are the backbone of Indian atmospheric dynamics research, and the release explicitly highlights their indigenous development
ARIES's other claim on the exam syllabus is the Devasthal observatory site in Uttarakhand, home to the 3.6-metre optical telescope — the same institute appears in both astronomy and atmospheric-science questions
GS Paper 1 > Geography > Atmosphere; GS Paper 3 > Science and Technology, Environment
General Awareness > Science and Environment
Ozone, the Montreal Protocol family of treaties and Indian research institutes recur regularly across Prelims
The stratospheric circulation in which tropical tropospheric air rises into the stratosphere, moves poleward and descends at higher latitudes, redistributing ozone away from where it is produced
The standard unit for measuring total column ozone in the atmosphere
Stratosphere-Troposphere Radar — a ground-based radar measuring winds and vertical air motion through the troposphere and lower stratosphere; ARIES operates an indigenously developed 206.5 MHz system at Nainital
A nationwide coordinated Indian atmospheric research campaign using a network of radars and balloon-borne instruments; its Phase-I produced this finding