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| Titel |
Effects of along- and cross-radar-beam winds on Doppler radar spectrum |
| VerfasserIn |
Y.-H. Chu |
| 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 ; 23, no. 3 ; Nr. 23, no. 3 (2005-03-30), S.681-692 |
| Datensatznummer |
250015171
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| Publikation (Nr.) |
 copernicus.org/angeo-23-681-2005.pdf |
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| Zusammenfassung |
| Beam broadening effects on the Doppler radar spectrum induced by along- and
cross-radar-beam winds are theoretically investigated in this article.
Analytical expression of beam broadening spectrum for a vertical beam
subject to a constant vertical wind in the absence of horizontal wind is
derived first. We find that the resultant beam broadening spectral shape is
in an exponential form, rather than a Gaussian shape. The peak of the
exponential spectrum corresponds to the true vertical wind velocity, and the
spectral width σ is a function of vertical wind velocity w and the
half-power beam width θ1/2 of the radar beam, in accordance with the
expression σ=0.09wθ1/22. The beam broadening
spectrum for a vertical radar beam subject to both vertical and horizontal
winds is numerically studied, and the result shows that the spectral shape
is distorted from the Gaussian form. The estimated vertical wind velocity of
the distorted spectrum is very close to the true vertical wind velocity with
a difference of less than 0.6% for a typical case. However, its spectral
width is substantially greater than that of the conventional Gaussian
spectrum broadened by horizontal wind only. The difference of the spectral
widths Δσ (in unit of percentage) in the two, as a function
of the half-power beam width and the ratio of vertical to horizontal wind
velocities, can be well approximated by a parabolic equation. With this
equation and the conventional Gaussian beam broadening spectral width caused
by horizontal wind, the true width of the distorted beam broadening spectrum
induced by vertical and horizontal winds can be inferred without complicated
numerical computation. Through a transformation of wind velocity from
vertical and horizontal winds into along- and cross-radar-beam winds defined
on the cross section of an oblique radar beam, the results obtained from the
case of vertical radar beam can be directly applied to the case of the oblique
beam. We show that in some special cases the beam broadening spectral widths
of an oblique beam subject to both vertical and horizontal winds will be
exceedingly narrower than those estimated by the existing formula, irrespective
of the presence of strong horizontal wind velocity. |
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