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| Titel |
The contribution of Kelvin waves in the forcing of the QBO and SAO derived from SABER and ECMWF temperatures |
| VerfasserIn |
M. Ern, P. Preusse |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023949
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| Zusammenfassung |
| The quasi-biennial oscillation (QBO) of the zonal mean zonal wind is one of the most
important processes in the dynamics of the middle atmosphere in the tropics. The phase
descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of
both global scale (equatorial wave modes like Kelvin or Rossby-gravity waves), as well as
mesoscale gravity waves. However, the relative distribution of the different types of waves to
the forcing of the QBO winds is highly uncertain. This is the case because until recently there
were no high resolution long-term global measurements in the stratosphere. With the new
satellite instruments SABER and HIRDLS, as well as the COSMIC GPS receivers, this
situation now has changed. At higher altitudes, in the upper stratosphere and in the
mesosphere, one of the most prominent processes in the dynamics of the tropics
is the semi-annual oscillation (SAO) of the zonal mean zonal wind. We estimate
momentum fluxes and the contribution of zonal wind forcing by Kelvin waves based on
space-time spectra determined from both SABER temperature measurements as well as
ECMWF temperatures. Peak values of total Kelvin wave zonal wind forcing are about
0.2 m/s/day. Global distributions are shown and the results are compared to the total wave
forcing required to balance the background atmosphere. It is found that there is good
agreement between SABER and ECMWF results. During some periods Kelvin
wave forcing is sufficient to explain almost the whole total wave forcing required
for the momentum balance of the QBO, while in other periods the contribution
of Kelvin waves is comparably low. Also the contribution of Kelvin wave wind
forcing to the forcing of the SAO in the upper stratosphere and in the mesosphere is
low. |
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