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| Titel |
The diurnal and semidiurnal tides over Ascension Island (° S, 14° W) and their interaction with the stratospheric quasi-biennial oscillation: studies with meteor radar, eCMAM and WACCM |
| VerfasserIn |
R. N. Davis, J. Du, A. K. Smith, W. E. Ward, N. J. Mitchell |
| 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 ; 13, no. 18 ; Nr. 13, no. 18 (2013-09-27), S.9543-9564 |
| Datensatznummer |
250085716
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| Publikation (Nr.) |
 copernicus.org/acp-13-9543-2013.pdf |
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| Zusammenfassung |
| Horizontal winds in the mesosphere have been measured over Ascension Island
(8° S, 14° W) in the tropical mid-Atlantic region throughout
the years 2002–2011. The observations were made by a very high frequency (VHF) meteor radar. The
observations reveal the presence of atmospheric tides of large amplitude. The
observations are analysed to characterise the seasonal and interannual
variability of the diurnal and semidiurnal tides. Monthly-mean diurnal tidal
amplitudes are found to reach values as large as 48 m s−1 in the
meridional component and 41 m s−1 in the zonal. A semiannual seasonal
variation is found in diurnal tidal amplitudes with amplitude maxima at the
equinoxes and amplitude minima at the solstices. Diurnal tidal meridional
vertical wavelengths are generally in the range 24–30 km. The diurnal zonal
vertical wavelengths are similar to the meridional, except for the winter
months when the zonal vertical wavelengths are much longer, occasionally
exceeding 100 km. Semidiurnal amplitudes are observed to be significantly
smaller than diurnal amplitudes. Semidiurnal vertical wavelengths range from
20 to more than 100 km. Our observations of tidal amplitudes and phases are
compared with the predictions of the extended Canadian Middle Atmosphere
Model (eCMAM) and the Whole Atmosphere Community Climate Model (WACCM). Both
eCMAM and WACCM reproduce the trend for greater diurnal amplitudes in the
meridional component than the zonal. However, eCMAM tends to overestimate
meridional amplitudes, while WACCM underestimates both zonal and meridional
amplitudes. Vertical wavelength predictions are generally good for both
models; however, eCMAM predicts shorter diurnal zonal vertical wavelengths
than are observed in winter, while WACCM predicts longer zonal vertical
wavelengths than observed for the semidiurnal tide for most months.
Semidiurnal amplitude predictions are generally good for both models. It is
found that larger-than-average diurnal and semidiurnal tidal amplitudes occur
when the stratospheric quasi-biennial oscillation (QBO) at 10 hPa is eastwards, and smaller-than-average
amplitudes occur when it is westwards. Correlations between the amplitude
perturbations and the El Niño Southern Oscillation are also found. The
precise mechanism for these correlations remains unclear. |
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