Geoscience Reference
In-Depth Information
35
Figure 5.8 (a) Chlorine
chemistry associated with
stratospheric ozone
depletion. (b) Loss of ozone
over Antarctica in early
spring compared to early
winter. (After Bridgman, H.,
1997
, Figures 22.3 and 22.4
with permission from
Routledge)
UV RADIATION
McMurdo 78
°
S
Photodissociation
1991
30
F
C
CFC-11
(CFCL
3
)
Cl
F
25
Cl
Cl
C
Cl
Cl
CHLORINE
ATOM
20
Cl
O
OZONE (O
3
)
10 Oct
O
O
OXYGEN (O
2
)
O
15
CHLORINE
MONOXIDE (ClO)
O
Cl
O
23 Aug
MULTIPLE
REACTIONS
OXYGEN (O)
ATOM
10
O
O
Cl
CHLORINE
ATOM
OXYGEN (O
2
)
O
++
NO
2
5
CH
4
H
RESERVOIR
STORAGE
Cl
Cl
OOO
N
0
CHLORINE
NITRATE
(CLONO
2
)
0
5 10
O3 PARTIAL PRESSURE (mPa)
15
HYDROGEN
CHLORIDE
(NCI)
(a)
(b)
Most ozone loss occurs at altitudes between 13 and 23 km, with almost 100%
loss at the altitudes around 18 km. Aircraft and satellite data from several studies
have confirmed that the CPV, with the PNJ at its leading edge, is a clear barrier
between ozone destruction and ozone survival (Figure
5.8
). Finally, some time
between about mid-October and early November, the sunlight becomes strong
enough, and the polar-equatorial temperature gradient has become weak
enough, to diminish the circumpolar barrier. Meridional transport of mid-
latitude air resumes, and ozone levels recover in the Antarctic stratosphere.
The size and location of the circumpolar vortex and the area of major ozone
loss varies from year to year and day to day. It is strongly linked to the AAO.
Coastal research stations such as Neumayer and Halley Bay are far enough south
to generally remain within the vortex each year (K¨nig-Langlo et al.
1998
), and
ozone depletion in spring is regularly measured. Stations like Dumont d'Urville,
however, are under the leading edge of the vortex. Ozone loss here depends on
the spatial fluctuations of the vortex.
5.8 ESSAY: Arctic Climate
Gerd Wendler, University of Alaska
5.8.1 General observations
The definition of the Arctic is not uniform in the literature. We use here the
astronomical definition,
the Arctic Circle. Other authors have used a
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