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| Titel |
On the presence of equatorial waves in the lower stratosphere of a general circulation model |
| VerfasserIn |
P. Maury, F. Lott |
| 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. 4 ; Nr. 14, no. 4 (2014-02-18), S.1869-1880 |
| Datensatznummer |
250118410
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| Publikation (Nr.) |
 copernicus.org/acp-14-1869-2014.pdf |
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| Zusammenfassung |
To challenge the hypothesis that equatorial waves in the lower stratosphere
are essentially forced by convection, we use the LMDz atmospheric model
extended to the stratosphere and compare two versions having very different
convection schemes but no quasi-biennial oscillation (QBO). The two versions
have realistic time mean precipitation climatologies but very different
precipitation variabilities. Despite these differences, the equatorial
stratospheric Kelvin waves at 50 hPa are almost identical in the two
versions and quite realistic. The Rossby gravity waves are also very similar
but significantly weaker than in observations. We demonstrate that this bias
on the Rossby gravity waves is essentially due to a dynamical filtering
occurring because the model zonal wind is systematically westward. During a
westward phase of the QBO, the ERA-Interim Rossby gravity waves compare well
with those in the model.
These results suggest that (i) in the model the effect of the convection
scheme on the waves is in part hidden by the dynamical filtering, and (ii) the
waves are produced by other sources than equatorial convection. For the
Kelvin waves, this last point is illustrated by an Eliassen and Palm flux
analysis, showing that in the model they come more from the subtropics and
mid-latitude regions, whereas in the ERA-Interim reanalysis the sources are
more equatorial. We show that non-equatorial sources are also significant in
reanalysis data sets as they explain the presence of the Rossby gravity waves
in the stratosphere. To illustrate this point, we identify situations with
large Rossby gravity waves in the reanalysis middle stratosphere for dates
selected when the stratosphere is dynamically separated from the equatorial
troposphere. We refer to this process as a stratospheric reloading. |
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