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| Titel |
Climatology and trends in the forcing of the stratospheric zonal-mean flow |
| VerfasserIn |
E. Monier, B. C. Weare |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-16), S.12751-12771 |
| Datensatznummer |
250010276
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| Publikation (Nr.) |
 copernicus.org/acp-11-12751-2011.pdf |
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| Zusammenfassung |
| The momentum budget of the Transformed Eulerian-Mean (TEM) equation is
calculated using the European Centre for Medium-Range Weather Forecasts
(ECMWF) reanalysis (ERA-40) and the National Centers for Environmental
Prediction (NCEP) Reanalysis 2 (R-2). This study outlines the considerable
contribution of unresolved waves, deduced to be gravity waves, to the forcing
of the zonal-mean flow. A trend analysis, from 1980 to 2001, shows that the
onset and break down of the Northern Hemisphere (NH) stratospheric polar
night jet has a tendency to occur later in the season in the more recent
years. This temporal shift follows long-term changes in planetary wave
activity that are mainly due to synoptic waves, with a lag of one month. In
the Southern Hemisphere (SH), the polar vortex shows a tendency to persist
further into the SH summertime. This also follows a statistically significant
decrease in the intensity of the stationary EP flux divergence over the
1980–2001 period. Ozone depletion is well known for strengthening the polar
vortex through the thermal wind balance. However, the results of this work
show that the SH polar vortex does not experience any significant long-term
changes until the month of December, even though the intensification of the
ozone hole occurs mainly between September and November. This study suggests
that the decrease in planetary wave activity in November provides an
important feedback to the zonal wind as it delays the breakdown of the polar
vortex. In addition, the absence of strong eddy feedback before November
explains the lack of significant trends in the polar vortex in the SH early
spring. A long-term weakening in the Brewer-Dobson (B-D) circulation in the
polar region is identified in the NH winter and early spring and during the
SH late spring and is likely driven by the decrease in planetary wave
activity previously mentioned. During the rest of the year, there are large
discrepancies in the representation of the B-D circulation and the unresolved
waves between the two reanalyses, making trend analyses unreliable. |
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