Indian scientists observed an abnormally thick ozone layer at 21–23 km altitude over the North Bay of Bengal, with concentrations far above normal for eastern India and persisting for over 24 hours. Researchers from ARIES (Aryabhatta Research Institute of Observational Sciences), Nainital, and other institutions studied it under Phase-I of the NetRAD-ASMA campaign, using 206.5 MHz Stratosphere–Troposphere (ST) radars, weather balloons, satellites and atmospheric models. They found sustained downward air movement in the lower stratosphere and concluded that horizontal transport of ozone-rich air, sinking motion and air compression mainly caused the enhancement.