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| Titel |
The roles of vertical advection and eddy diffusion in the equatorial mesospheric semi-annual oscillation (MSAO) |
| VerfasserIn |
R. L. Gattinger, E. Kyrölä, C. D. Boone, W. F. J. Evans, K. A. Walker, I. C. McDade, P. F. Bernath, E. J. Llewellyn |
| 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. 15 ; Nr. 13, no. 15 (2013-08-14), S.7813-7824 |
| Datensatznummer |
250085625
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| Publikation (Nr.) |
 copernicus.org/acp-13-7813-2013.pdf |
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| Zusammenfassung |
| Observations of the mesospheric semi-annual oscillation (MSAO) in the
equatorial region have been reported dating back several decades. Seasonal
variations in both species densities and airglow emissions are well
documented. The extensive observations available offer an excellent case
study for comparison with model simulations. A broad range of MSAO
measurements is summarised with emphasis on the 80–100 km region. The
objective here is not to address directly the complicated driving forces of
the MSAO, but rather to employ a combination of observations and model
simulations to estimate the limits of some of the underlying dynamical
processes. Photochemical model simulations are included for near-equinox and
near-solstice conditions, the two times with notable differences in the
observed MSAO parameters. Diurnal tides are incorporated in the model to
facilitate comparisons of observations made at different local times. The
roles of water vapour as the "driver" species and ozone as the "response"
species are examined to test for consistency between the model results and
observations. The simulations suggest the interactions between vertical eddy
diffusion and background vertical advection play a significant role in the
MSAO phenomenon. Further, the simulations imply there are rigid limits on
vertical advection rates and eddy diffusion rates. For August at the Equator,
90 km altitude, the derived eddy diffusion rate is approximately
1 × 106 cm2 s−1 and the vertical advection is
upwards at 0.8 cm s−1. For April the corresponding values are
4 × 105 cm2 s−1 and 0.1 cm s−1. These results
from the current 1-D model simulations will need to be verified by a full 3-D
simulation. Exactly how vertical advection and eddy diffusion are related to
gravity wave momentum as discussed by Dunkerton (1982) three decades ago
remains to be addressed. |
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