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| Titel |
Characteristics of episodes with extremely low ozone values in the northern middle latitudes 1957-2000 |
| VerfasserIn |
R. D. Bojkov, D. S. Balis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 19, no. 7 ; Nr. 19, no. 7, S.797-807 |
| Datensatznummer |
250014290
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| Publikation (Nr.) |
 copernicus.org/angeo-19-797-2001.pdf |
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| Zusammenfassung |
A number of episodes are
observed when the total ozone for 2 to 3 days has fallen below 220 matm-cm in
the northern mid- and polar latitudes in autumn. The occurrences of such
episodes represent ozone deviations of about one-third from the pre-1976
Oct-Nov-Dec monthly mean! By using primarily quality checked Dobson data, a
clear identification was made of more than three dozen short spells with
extremely low ozone in the 1957–1978 period. In the following twenty-two
years (1979–2000), using mainly TOMS data, one can identify ~ 46 cases with
ozone values falling below 220 matm-cm for longer than 1 day, with each time
over an area greater than 500,000 km2 . The Ozone Mass Deficiency (O3MD)
from the pre-1976 average ozone values over the affected area was ~2.8 Mt per
day, i.e. four to seven times greater than it would be, assuming only a
long-term trend in the Oct-Nov-Dec period. The Extremely Low Ozone (ELO3)
events on the day of their appearance over the N. Atlantic/European region
contribute to the O3MD by representing 16% of the deficiency due to
the Oct-Nov trend in the entire 40–65° N latitudinal belt. The O3MD
of the greater pool with low ozone (here taken as <260 matm-cm) surrounding
the area of the lowest events could contribute on the day of their appearance
in Oct-Nov up to 60% and in December, ~30% to the deficiency due to the trend
over the entire 40–65° N belt. Analysis of synoptic charts, supported by a
backward trajectory on the isentropic surfaces 350 and 380 K, shows that in
most of the events, subtropical air masses with low ozone content were
transported from the Atlantic toward the UK, Scandinavia, and in many cases,
further to the western sub-polar regions of Russia. This transport was
sometimes combined with upward motions above a tropospheric anticyclone which
lifted low ozone mixing ratios to higher altitudes. The ELO3 events
cause a significant deficiency above the tropopause where, in general, the
subtropical air is injected. In fact, the overall amount of ozone is not
depleted, but redistributed on the hemispheric scale. Review of low ozone
events, defined as days with negative deviations from the pre-1976 averages
greater than 25% show, in general, similar origin. The seasonally averaged area
with ELO3 and the associated O3MD, as well as for the
cases with deviations > –25%, has increased during the 1990s, which could
be an indication of stronger and/or more frequent subtropical air intrusions.
Their occurrences could contribute noticeably to the ozone deficiency of the
middle latitude ozone during the days of ELO3 appearances; however,
their contribution to the long-term trend of the ozone seasonal decline is of
the order of ~10%.
Key words. Atmospheric composition
and structure (middle atmosphere - composition and chemistry) Meteorology and
atmospheric dynamics (middle atmosphere dynamics) |
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