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| Titel |
Zonal mean and tidal dynamics from space: an empirical examination of aliasing and sampling |
| VerfasserIn |
J. M. Forbes, M. Kilpatrick, D. Fritts, A. H. Manson, R. A. Vincent |
| 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 ; 15, no. 9 ; Nr. 15, no. 9, S.1158-1164 |
| Datensatznummer |
250012945
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| Publikation (Nr.) |
 copernicus.org/angeo-15-1158-1997.pdf |
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| Zusammenfassung |
| Interpretations of space-based measurements
of atmospheric parameters in the mesosphere and thermosphere are complicated by
large local-time variations at these altitudes. For this reason, satellite
orbits are often preferred which precess through all local times one or more
times per season. However, the local-time structure of the atmosphere is
inherently non-stationary, which can lead to sampling and aliasing difficulties
when attempting to deconvolve the measurements into zonal mean and tidal
components. In the present study, hourly radar measurements of mesopause-region
winds are used to form a mock data base which can be used to gain insight into
implications of the aforementioned problems; the use of actual measurements
introduces a realistic element of geophysical temporal variability. Assuming
zonal symmetry (i.e., migrating tides superimposed on a zonal mean circulation),
the radar measurements are sampled from the satellite perspective for orbital
inclinations of 57° and 70°, and compared to the ground or true
perspective. These comparisons provide realistic estimates of the errors to be
expected when attempting to derive mean and tidal components from space-based
measurements. For both diurnal and semidiurnal components, and the quoted
satellite inclinations, acceptable errors (3–4m/srms) are obtained for data
covering 24h local time (i.e., ascending plus descending nodes); the
corresponding errors for single-node data (12h local-time coverage) are of order
8–11m/s, and therefore may not represent reliable estimates of the actual tidal
components. There exist certain caveats in connection with the latter conclusion
which are discussed. |
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