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| Titel |
Analysing time-varying trends in stratospheric ozone time series using the state space approach |
| VerfasserIn |
M. Laine, N. Latva-Pukkila, E. Kyrölä |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-16), S.9707-9725 |
| Datensatznummer |
250119037
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| Publikation (Nr.) |
 copernicus.org/acp-14-9707-2014.pdf |
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| Zusammenfassung |
We describe a hierarchical statistical state space model for ozone profile
time series. The time series are from satellite measurements by the
Stratospheric Aerosol and Gas Experiment (SAGE) II and the Global Ozone
Monitoring by Occultation of Stars (GOMOS) instruments spanning the years
1984–2011. Vertical ozone profiles were linearly interpolated on an altitude
grid with 1 km resolution covering 20–60 km. Monthly averages were
calculated for each altitude level and 10° wide latitude bins
between 60° S and 60° N. In the analysis, mean densities
are studied separately for the 25–35, 35–45, and 45–55 km layers. Model
variables include the ozone mean level, local trend, seasonal oscillations,
and proxy variables for solar activity, the Quasi-Biennial Oscillation (QBO),
and the El Niño–Southern Oscillation (ENSO).
This is a companion paper to Kyrölä et al. (2013), where a piecewise linear
model was used together with the same proxies as in this work (excluding
ENSO). The piecewise linear trend was allowed to change at the beginning of
1997 in all latitudes and altitudes. In the modelling of the present paper
such an assumption is not needed as the linear trend is allowed to change
continuously at each time step. This freedom is also allowed for the seasonal
oscillations whereas other regression coefficients are taken independent of
time. According to our analyses, the slowly varying ozone background shows
roughly three general development patterns. A continuous decay for the whole
period 1984–2011 is evident in the southernmost latitude belt
50–60° S in all altitude regions and in 50–60° N in the
lowest altitude region 25–35 km. A second pattern, where a recovery after
an initial decay is followed by a further decay, is found at northern
latitudes from the equator to 50° N in the lowest altitude region
(25–35 km) and between 40° N and 60° N in the
35–45 km altitude region. Further ozone loss occurred after 2007 in these
regions. Everywhere else a decay is followed by a recovery. This pattern is
shown at all altitudes and latitudes in the Southern Hemisphere
(10–50° S) and in the 45–55 km layer in the Northern Hemisphere
(from the equator to 40° N). In the 45–55 km range the trend,
measured as an average change in 10 years, has mostly turned from negative
to positive before the year 2000. In those regions where the "V" type of
change of the trend is appropriate, the turning point is around the years
1997–2001. To compare results for the trend changes with the companion
paper, we studied the difference in trends between the years from 1984 to
1997 and from 1997 to 2011. Overall, the two methods produce very similar
ozone recovery patterns with the maximum trend change of 10% in
35–45 km. The state space method (used in this paper) shows a somewhat
faster recovery than the piecewise linear model. For the percent change of
the ozone density per decade the difference between the results is below three
percentage units. |
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