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| Titel |
Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere |
| VerfasserIn |
H. Luce, G. Hassenpflug, M. Yamamoto, S. Fukao |
| 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 ; 25, no. 1 ; Nr. 25, no. 1 (2007-02-01), S.47-57 |
| Datensatznummer |
250015762
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| Publikation (Nr.) |
 copernicus.org/angeo-25-47-2007.pdf |
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| Zusammenfassung |
| Many experimental studies have demonstrated that VHF
Stratosphere-Troposphere (ST) radar echo power is proportional to the
generalized refractive index gradient squared M2 when using a vertically
oriented beam. Because humidity is generally negligible above the
tropopause, VHF ST radars can thus provide information on the static
stability (quantified by the squared Brunt-Väisälä frequency
N2) at stratospheric heights and this capability is useful for many
scientific applications. Most studies have been performed until now at a
vertical resolution of 150 m or more. In the present paper, results of
comparisons between radar- and (balloon borne) radiosonde-derived M2 and
N2 are shown at a better vertical resolution of 50 m with the MU
radar (34.85° N, 136.15° E; Japan) by benefiting from the range
resolution improvement provided by the multi-frequency range imaging
technique, using the Capon processing method. Owing to favorable winds in the
troposphere, the radiosondes did not drift horizontally more than about 30 km
from the MU radar site by the time they reached an altitude of 20 km.
The measurements were thus simultaneous and almost collocated. Very good
agreements have been obtained between both high resolution profiles of M2,
as well as profiles of N2. It is also shown that this agreement can
still be improved by taking into account a frozen-in advection of the air
parcels by a horizontally uniform wind. Therefore, it can be concluded that
1) the range imaging technique with the Capon method really provides
substantial range resolution improvement, despite the relatively weak Signal-to-Noise
Ratios (SNR) over the analyzed region of the lower stratosphere, 2)
the proportionality of the radar echo power to M2 at a vertical scale
down to 50 m in the lower stratosphere is experimentally demonstrated,
3) the MU radar can provide stability profiles with a vertical resolution of
50 m at heights where humidity is negligible, 4) stable stratospheric layers
as thin as 50 m or less have at least a horizontal extent of a few km
to several tens of kilometers and can be considered as frozenly advected
over scales of a few tens of minutes. |
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