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| Titel |
Temperature sheets and aspect sensitive radar echoes |
| VerfasserIn |
H. Luce, M. Crochet, F. Dalaudier |
| 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 ; 19, no. 8 ; Nr. 19, no. 8, S.899-920 |
| Datensatznummer |
250014301
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| Publikation (Nr.) |
 copernicus.org/angeo-19-899-2001.pdf |
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| Zusammenfassung |
here have been years of
discussion and controversy about the existence of very thin and stable
temperature sheets and their relationship to the VHF radar aspect sensitivity.
It is only recently that very high-resolution in situ temperature observations
have brought credence to the reality and ubiquity of these structures in the
free atmosphere and to their contribution to radar echo enhancements along the
vertical. Indeed, measurements with very high-resolution sensors are still
extremely rare and rather difficult to obtain outside of the planetary boundary
layer. They have only been carried out up to the lower stratosphere by Service
d’A´ eronomie (CNRS, France) for about 10 years. The controversy also
persisted due to the volume resolution of the
(Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect
to sheet thickness, although widely sufficient for meteorological or mesoscale
investigations. The contribution within the range gate of many of these
structures, which are advected by the wind, and decay and grow at different
instants and could be distorted either by internal gravity waves or turbulence
fields, could lead to radar echoes with statistical properties similar to those
produced by anisotropic turbulence. Some questions thus remain regarding the
manner in which temperature sheets contribute to VHF radar echoes. In
particular, the zenithal and azimuthal angular dependence of the echo power may
not only be produced by diffuse reflection on stable distorted or corrugated
sheets, but also by extra contributions from anisotropic turbulence occurring
in the stratified atmosphere. Thus, for several years, efforts have been put
forth to improve the radar height resolution in order to better describe thin
structures. Frequency interferometric techniques are widely used and have been
recently further developed with the implementation of high-resolution data
processings. We begin by reviewing briefly some characteristics of the ST radar
echoes with a particular emphasis on recent works. Their possible coupling with
stable sheets is then presented and their known characteristics are described
with some hypotheses concerning their generation mechanisms. Finally,
measurement campaigns that took recently place or will be carried out in the
near future for improving our knowledge of these small-scale structures are
presented briefly.
Key words. Meteorology and
atmospheric dynamics (turbulence; instruments and techniques) – Radio Science
(remote sensing) |
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