Differentiate between photochemical and dynamical processes responsible for ozone distribution in the stratosphere, with reference to recent Indian findings over the Bay of Bengal.

Stratospheric ozone, concentrated normally at 25–30 km, is governed by two distinct controls: photochemical processes that create and destroy ozone molecules, and dynamical processes that merely transport and redistribute them. A recent ARIES-led Indian study over the North Bay of Bengal shows that the dynamical control can dominate observed ozone maxima [1].

Photochemical processes — production and loss

• Chapman mechanism: solar ultraviolet radiation splits oxygen molecules, whose atoms combine with O₂ to form ozone; destruction occurs through photolysis and catalytic cycles.
• Strictly sunlight-dependent, hence strongest over the tropics at high altitudes and active only in daytime.
• Chemically alters the total ozone amount; this is the pathway disturbed by ozone-depleting substances regulated under the Montreal Protocol.

Dynamical processes — transport and redistribution

• Ozone-rich air is advected by stratospheric circulation, then subjected to downward motion (subsidence) and compression, concentrating ozone at lower levels [1].
• Conserves total ozone but changes its vertical and spatial distribution; operates independent of sunlight, so it works equally by day and night.
• Dominant in the extra-tropics and subtropics, especially in winter, where ozone lifetimes are long.

Evidence from the Bay of Bengal finding

• Indian scientists recorded an unusually thick ozone layer at 21–23 km — below the normal peak — persisting over a day [1].
• Data from the indigenous 206.5 MHz Stratosphere–Troposphere Radar network (Haringhata, Gadanki, Kochi) under the Phase-I NetRAD-ASMA campaign, with balloon soundings and Aura MLS and INSAT-3DR satellite data, traced it to transport plus subsidence [1][2].
• Crucially, the enhancement appeared in both day and night, ruling out photochemical production [1].

Thus the two processes are complementary rather than competing: chemistry sets the ozone budget, dynamics decides where it resides. Strengthening indigenous radar networks and multi-platform observation campaigns will sharpen India's atmospheric models, aiding UV-risk assessment and climate research aligned with SDG-13.