Polar Atmosphere Phenomena
: Focusing on the Polar Vortex
Destruction of the Ozone layer
1. Relationship between the Polar Vortex, PSC Volume, and Ozone Concentration
(a) In 2021, 2020, and 2006, lower stratospheric temperatures in the Southern Hemisphere remained consistently below average throughout the winter–spring period. This represents the typical state of a strong polar vortex.
(b) PSC Volume: In September, PSC volume increased above average. Extremely low temperatures promoted PSC formation, and heterogeneous reactions on PSC surfaces activated chlorine (ClO).
(c) ClO: ClO concentrations stayed near average until mid-September, but surged above average in early October as sunlight returned, triggering catalytic ozone destruction.
(d) O₃: In 2021, ozone loss between July and October was about 2.22 ppmv, comparable to the losses in the unusually cold years of 2020 and 2006. This confirms that strong vortex conditions and low temperatures directly translated into substantial ozone depletion.
(e) Ozone Hole Area: On 7 October 2021, the hole reached a maximum of 24.8 × 10⁶ km². The enlarged hole persisted until late December, making it one of the longest-lasting ozone holes on record.
(f) South Pole 12–20 km Column: From October through December, values remained consistently below average. Even after PSCs and ClO declined to near zero by mid-October, the strong vortex continued to block the influx of ozone-rich midlatitude air, delaying recovery.
The graph above illustrates the sequence of processes through which the ozone layer is destroyed.
First, it is winter in the Southern Hemisphere in July, so temperatures are low and gradually increase toward December. When the temperature is low, the formation of Polar Stratospheric Clouds (PSC) is promoted. On the surface of PSC, reactions occur that convert HCl and ClONO₂ into ClO.
As spring arrives and the temperature rises, sunlight activates ClO, which then acts as a catalyst to destroy O₃. This leads to a reduction in the absorption of ultraviolet radiation. Consequently, the temperature of the polar stratosphere decreases, enhancing the temperature difference between the polar regions and the mid-latitudes. This accelerates the jet stream, resulting in a strong and stable polar vortex.
2. Period of Strong Polar Vortex: Daily Polar Vortex Area in 2006
In 2006, the polar vortex area remained within its maximum range.
The large PSC area further indicates that the necessary chemical conditions for chlorine activation were present.
3. Comparison of October–November Average Ozone Hole Area
by Year Since 1979 and Vertical Ozone Distribution
In 2006, the average ozone hole size reached 18.0 million km², the largest on record. Also, observations of the vertical ozone distribution over the South Pole revealed near-complete depletion of ozone in the 13–21 km altitude range.
4. Relationship Between Polar Vortex Persistence and Ozone Hole Persistence
In 2006, the polar vortex persisted longer than in any other year. Linking this to Data 2&3, which show that the vortex was also at its strongest in 2006, it can be inferred that a strong polar vortex contributed significantly to the enlargement of the ozone hole.