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| Titel |
Sub-daily excitation of Earth rotation by atmospheric tides |
| VerfasserIn |
Michael Schindelegger, Johannes Böhm, David Salstein, Harald Schuh |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051374
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| Zusammenfassung |
| Sub-daily signals in atmospheric excitation of Earth rotation are usually investigated
with atmospheric angular momentum (AAM) functions that are estimated from the
operational analysis fields of Numerical Weather Models. The temporal resolution of
these data is typically six hours, limiting the spectral resolution of polar motion
and LOD variations in the semi-diurnal band. In this study, though, we use the
so-called delayed cut-off stream of the European Centre for Medium-Range Weather
Forecasts (ECMWF) to determine three-hourly AAM functions for the time span
July 2004 to July 2010 to aid in the analysis of sub-daily signals. The resulting
amplitudes and phases in the diurnal and semi-diurnal equatorial and axial excitation
spectra are generally below 2 μas and 4 μs, but they fit well to the estimates from
the corresponding six-hourly AAM record based on data from the U.S. National
Centers for Environmental Prediction (NCEP). The three-hourly data, however,
allow a more detailed insight into the atmospheric state and circulation, causing the
well-observed semi-diurnal (S2) signals in Earth rotation. Both for the AAM functions, and
for the original meteorological data, a phase-shift of ±Ï prevails between the S2
pressure signal and the resulting S2 wind tide, leading to a distinct counteraction of
pressure and wind terms in the excitation spectra. This finding is in agreement with the
theoretical work on atmospheric tides by Chapman and Lindzen (1970) and others. |
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