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| Titel |
Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages |
| VerfasserIn |
J. G. Yoe, P. Czechowsky, R. Rüster, G. Schmidt |
| 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 ; 12, no. 8 ; Nr. 12, no. 8, S.733-745 |
| Datensatznummer |
250011032
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| Publikation (Nr.) |
 copernicus.org/angeo-12-733-1994.pdf |
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| Zusammenfassung |
| The aspect sensitivity of SOUSY-VHF-radar
oblique-beam echoes from the troposphere and lower stratosphere has been
examined for a number of jet stream passages during the years 1990 - 1992. When
the core of the jet is overhead or nearly so, vertical profiles of the aspect
sensitivity display two notable features. First, the distinction between mainly
isotropic and strongly aspect-sensitive echoes in the troposphere and the lower
stratosphere, respectively, often reported for measurements made during calm
conditions, does not necessarily prevail in the vicinity of the jet stream.
Second, echoes obtained at altitudes near the height of the horizontal wind
maximum are found to be more aspect sensitive for beams directed parallel to the
horizontal flow or nearly so, than for other beam directions. It is demonstrated
that time-averaged horizontal wind speeds estimated from the radar data, taking
into account the reduced effective oblique-beam zenith angle resulting from
aspect sensitivity, may exceed uncorrected wind speeds by as much as 10 m s-1
in these circumstances. Implications for wind profiling and for describing the
backscattering process are discussed. Doppler spectral widths examined for one
jet stream passage are found to be narrower in a beam aligned with the
horizontal wind at heights near the wind speed maximum than corresponding widths
measured in a beam projected at right angles to the jet. The narrowest spectra
thus coincide with the most aspect-sensitive echoes, consistent with the
hypothesis that such returns result from specular backscattering processes. |
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