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| Titel |
Equatorial annual oscillation with QBO-driven 5-year modulation in NCEP data |
| VerfasserIn |
H. G. Mayr, J. G. Mengel, F. T. Huang, E. R. Nash |
| 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 ; 25, no. 1 ; Nr. 25, no. 1 (2007-02-01), S.37-45 |
| Datensatznummer |
250015761
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| Publikation (Nr.) |
 copernicus.org/angeo-25-37-2007.pdf |
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| Zusammenfassung |
| An analysis is presented of the stratospheric zonal
wind and temperature variations supplied by the National Center for
Environmental Prediction (NCEP). The derived zonal-mean variations are
employed. Stimulated by modeling studies, the data are separated into the
hemispherically symmetric and anti-symmetric components, and spectral
analysis is applied to study the 12-month annual oscillation (AO) and the
quasi-biennial oscillation (QBO). For data samples that cover as much as 40
years, the zonal wind results reveal a pronounced 5-year modulation of the
symmetric AO in the lower stratosphere, which is confined to equatorial
latitudes. This modulation is also seen in the temperature variations but
extends to high latitudes, qualitatively consistent with published model
results. A comparison between different time intervals of the data indicates
that the signature of the 5-year oscillation is larger when the QBO of 30
months is more pronounced. Thus there is circumstantial evidence that this
particular QBO period is involved in generating the oscillation as was shown
in a modeling study (Mayr et al., 2000). In agreement with the model,
the spectral analysis also reveals a weak anti-symmetric 5-year oscillation
in the zonal wind data, which could interact with the strong anti-symmetric
AO to produce the modulation of the symmetric AO. The 30-month QBO is well
suited to be synchronized by, and phase-locked to, the equatorial
semi-annual oscillation (SAO), and this may explain why this QBO periodicity
and its 5-year spin-off are observed to persist for many cycles. |
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