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| Titel |
Quasi-biennial oscillation of the tropical stratospheric aerosol layer |
| VerfasserIn |
R. Hommel, C. Timmreck, M. A. Giorgetta, H. F. Graf |
| 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 ; 15, no. 10 ; Nr. 15, no. 10 (2015-05-21), S.5557-5584 |
| Datensatznummer |
250119742
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| Publikation (Nr.) |
 copernicus.org/acp-15-5557-2015.pdf |
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| Zusammenfassung |
This study describes how aerosol in an aerosol-coupled climate model of the
middle atmosphere is influenced by the quasi-biennial oscillation (QBO)
during times when the stratosphere is largely unperturbed by volcanic
material. In accordance with satellite observations, the vertical extent of
the stratospheric aerosol layer in the tropics is modulated by the QBO by up
to 6 km, or ~ 35% of its mean vertical extent between
100–7 hPa (about 16–33 km). Its largest vertical extent
lags behind the occurrence of strongest QBO westerlies. The largest reduction
lags behind maximum QBO easterlies. Strongest QBO signals in the aerosol
surface area (30 %) and number densities (up to 100% e.g. in the Aitken
mode) are found in regions where aerosol evaporates, that is above the
10 hPa pressure level (~ 31 km). Positive modulations
are found in the QBO easterly shear, negative modulations in the westerly
shear. Below 10 hPa, in regions where the aerosol mixing ratio is
largest (50–20 hPa, or ~ 20–26 km), in most of the
analysed parameters only moderate statistically significant QBO signatures
(< 10%) have been found.
QBO signatures in the model prognostic aerosol mixing ratio are significant
at the 95% confidence level throughout the tropical stratosphere where
modelled mixing ratios exceed 0.1 ppbm. In some regions of the
tropical lower stratosphere the QBO signatures in other analysed parameters are partly not
statistically significant. Peak-to-peak amplitudes of the QBO signature in
the prognostic mixing ratios are up to twice as large as seasonal variations
in the region where aerosols evaporate and between 70–30 hPa.
Between the tropical tropopause and 70 hPa the QBO signature is
relatively weak and seasonal variations dominate the variability of the
simulated Junge layer. QBO effects on the upper lid of the tropical aerosol
layer turn the quasi-static balance between processes maintaining the layer's
vertical extent into a cyclic balance when considering this dominant mode of
atmospheric variability. Global aerosol-interactive models without a QBO are
only able to simulate the quasi-static balance state. To assess the global
impact of stratospheric aerosols on climate processes, those partly
nonlinear relationships between the QBO and stratospheric aerosols have to
be taken into account. |
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