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| Titel |
Fresnel scatter revisited – comparison of 50 MHz radar and radiosondes in the Arctic, the Tropics and Antarctica |
| VerfasserIn |
S. Kirkwood  , E. Belova, K. Satheesan, T. Narayana Rao, T. Rajendra Prasad, S. Satheesh Kumar |
| 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 ; 28, no. 10 ; Nr. 28, no. 10 (2010-10-29), S.1993-2005 |
| Datensatznummer |
250016905
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1993-2010.pdf |
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| Zusammenfassung |
| High-resolution radiosondes and calibrated radars operating close to 50 MHz,
are used to examine the relationship between the strength of radar scatter
and refractive index gradient. Three radars are used, in Kiruna in Arctic
Sweden, at Gadanki in southern India and at the Swedish/Finnish base
Wasa/Aboa in Queen Maud Land, Antarctica. Calibration is accomplished using
the daily variation of galactic noise measured at each site. Proportionality
between radar scatter strength and the square of the mean gradient of
potential refractive index, M2, is found in the upper troposphere and
lower stratosphere at all three sites, confirming previously reported results
from many VHF radars. If the radar scatter is interpreted as Fresnel scatter,
the constant of proportionality between radar scatter and M2 is found to
be the same, within the calibration uncertainties, for all three radars. The
radiosondes show evidence of distinct layering with sharp gradients,
extending over 10s of kilometers horizontally, but the scatter is found to
be two orders of magnitude weaker than would be expected from true Fresnel
scatter from such layers. Using radar reflectivities resolved to a few 100 ms,
we show that this is due to strong temporal variability in the scattering
conditions, possibly due to undulations of the scattering layers. The
constancy of the radar scatter – M2 relationship between the different
sites suggests an unexpected uniformity in these perturbations between very
different regions of the globe. |
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