THE “HOLE”: A RESULT OF SPECIAL WEATHER CONDITIONS OVER THE POLE REPEATED EVERY SPRING THE “HOLE”: A RESULT OF SPECIAL WEATHER CONDITIONS OVER THE POLE REPEATED EVERY SPRING
Million square kilometres Average areas between 1995 and 2004
“The Antarctic continent is circled by a strong wind in the stratosphere which flows around Antarctica and isolates air over Antarctica from air in the midlatitudes. The region poleward of this jet stream is called the Antarctic polar vortex ( 1 ) . The air inside the Antarctic polar vortex is much colder than midlatitude air.” “When temperatures drop below -78°C, thin clouds form of ice, nitric acid, and sulphuric acid mixtures ( 2 ) . Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears ( 3 ) . In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.”
1 Vortex area
2 Polar stratospheric cloud area
Citations from the NASA Ozone Hole Watch website and Jeannie Allen, of the NASA Earth Observatory (February 2004).
3 Ozone hole area
Antarctic Spring Source: US National Oceanic and Atmospheric Administration (NOAA), 2006.
THE COLDER ANTARCTIC WINTER DRIVES FORMATION OF THE HOLE IN THE SOUTH THE COLDER ANTARCTIC WINTER DRIVES FORMATION OF THE HOLE IN THE SOUTH
Average temperature (1978 to 2006) Degrees Celsius
Arctic (North Pole)
Temperature under which a polar strato- spheric cloud can form.
Antarctic (South Pole)
Conditions for accelerated ozone depletion
Source: Twenty Questions and Answers about the Ozone Layer: 2006 Update , Lead Author: D.W. Fahey, Panel Review Meeting for the 2006 ozone assessment.