16
THE “HOLE”: A RESULT OF SPECIAL WEATHER CONDITIONS OVER THE POLE
REPEATED EVERTHE “HOLE”: A RESULY SPRING T OF SPECIAL WEATHER CONDITIONS
OVER THE POLE REPEATED EVERY SPRING
Average areas between 1995 and 2004
Million square kilometres
“The Antarctic continent is circled by a strong wind in
the stratosphere which flows around Antarctica and
35 isolates air over Antarctica from air in the midlatitudes.
1 Vortex area
The region poleward of this jet stream is called the
Antarctic polar vortex ( 1 ). The air inside the Antarctic
30
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 ).
25
2 Polar stratospheric
Chemical reactions on the surfaces of ice crystals in
the clouds release active forms of CFCs. Ozone
cloud area depletion begins, and the ozone “hole”
appears ( 3 ).
20
In spring, temperatures begin to rise, the
ice evaporates, and the ozone layer
starts to recover.”
15 Citations from the NASA Ozone
Hole Watch website and Jeannie
Allen, of the NASA Earth
10
Observatory (February 2004).
5
3 Ozone hole area
0
August September October November December
Antarctic Spring
Source: US National Oceanic and Atmospheric Administration (NOAA), 2006.
THE COLDER ANT
THE COLDER ANT
ARCTIC WINTER DRIVES FORMA
ARCTIC WINTER DRIVES
TION OF THE HOLE IN THE SOUTH
FORMATION OF THE HOLE IN THE SOUTH
Arctic Winter
November December January February March April
Average temperature (1978 to 2006)
Degrees Celsius
-60
-65
-70
-75 Arctic (North Pole)
Temperature
-80
under which a
polar strato-
spheric cloud
-85
can form.
Antarctic (South Pole)
-90
Conditions for
accelerated ozone depletion
-95
May June July August September October
Antarctic Winter
Source: Twenty Questions and Answers about the Ozone Layer: 2006 Update, Lead Author: D.W. Fahey,
Panel Review Meeting for the 2006 ozone assessment.
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