14 Regional and Seasonal Variation (Ozone layer)
Description
This article is from the Ozone Depletion FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.
14 Regional and Seasonal Variation (Ozone layer)
Since solar radiation makes ozone, one expects to see the
thickness of the ozone layer vary during the year. This is so,
although the details do not depend simply upon the amount of solar
radiation received at a given latitude and season - one must also
take atmospheric motions into account. (Remember that
both production and destruction of ozone require solar radiation.)
The ozone layer is thinnest in the tropics, about 260 DU, almost
independent of season. Away from the tropics seasonal variations
become important. For example:
Location Column thickness, Dobson Units
Jan Apr Jul Oct
Huancayo, Peru (12 degrees S) : 255 255 260 260
Aspendale, Australia (38 deg. S): 300 280 335 360
Arosa, Switzerland (47 deg. N): 335 375 320 280
St. Petersburg, Russia (60 deg. N): 360 425 345 300
These are monthly averages. Interannual standard deviations amount
to ~5 DU for Huancayo, 25 DU for St. Petersburg. [Rowland 1991].
Day-to-day fluctuations can be quite large (as much as 60 DU at high
latitudes). Notice that the highest ozone levels are found in the
_spring_, not, as one might guess, in summer, and the lowest in the
fall, not winter. Indeed, at high latitudes in the Northern Hemisphere
there is more ozone in January than in July! Most of the ozone is
created over the tropics, and then is carried to higher latitudes
by prevailing winds (the general circulation of the stratosphere.)
[Dobson 1968a] [Garcia] [Salby and Garcia] [Brasseur and Solomon]
The antarctic ozone hole, discussed in detail in Part III, falls
far outside this range of natural variation. Mean October ozone
at Halley Bay on the Antarctic coast was 117 DU in 1993, down
from 321 DU in 1956.
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