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| Titel |
A statistical study of underestimates of wind speeds by VHF radar |
| VerfasserIn |
L. Thomas, I. Astin, R. M. Worthington |
| 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. 6 ; Nr. 15, no. 6, S.805-812 |
| Datensatznummer |
250012843
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| Publikation (Nr.) |
 copernicus.org/angeo-15-805-1997.pdf |
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| Zusammenfassung |
| Comparisons are made between horizontal wind
measurements carried out using a VHF-radar system at Aberystwyth (52.4°N, 4.1°W)
and radiosondes launched from Aberporth, some 50 km to the south-west. The radar
wind results are derived from Doppler wind measurements at zenith angles of 6°
in two orthogonal planes and in the vertical direction. Measurements on a total
of 398 days over a 2-year period are considered, but the major part of the study
involves a statistical analysis of data collected during 75 radiosonde flights
selected to minimise the spatial separation of the two sets of measurements.
Whereas good agreement is found between the two sets of wind direction,
radar-derived wind speeds show underestimates of 4–6% compared with radiosonde
values over the height range 4–14 km. Studies of the characteristics of this
discrepancy in wind speeds have concentrated on its directional dependence, the
effects of the spatial separation of the two sets of measurements, and the
influence of any uncertainty in the radar measurements of vertical velocities.
The aspect sensitivity of radar echoes has previously been suggested as a cause
of underestimates of wind speeds by VHF radar. The present statistical treatment
and case-studies show that an appropriate correction can be applied using
estimates of the effective radar beam angle derived from a comparison of echo
powers at zenith angles of 4.2° and 8.5°. |
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