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| Titel |
E-region decameter-scale plasma waves observed by the dual TIGER HF radars |
| VerfasserIn |
B. A. Carter, R. A. Makarevich |
| 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 ; 27, no. 1 ; Nr. 27, no. 1 (2009-01-15), S.261-278 |
| Datensatznummer |
250016368
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| Publikation (Nr.) |
 copernicus.org/angeo-27-261-2009.pdf |
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| Zusammenfassung |
| The dual Tasman International Geospace Environment Radar (TIGER)
HF radars regularly observe E-region echoes at sub-auroral
magnetic latitudes 58°–60° S including during
geomagnetic storms. We present a statistical analysis of E-region
backscatter observed in a period of ~2 years (late
2004–2006) by the TIGER Bruny Island and Unwin HF radars, with
particular emphasis on storm-time backscatter. It is found that
the HF echoes normally form a 300-km-wide band at ranges
225–540 km. In the evening sector during geomagnetic storms,
however, the HF echoes form a curved band joining to the F-region
band at ~700 km. The curved band lies close to the locations
where the geometric aspect angle is zero, implying little to no
refraction during geomagnetic storms, which is an opposite result
to what has been reported in the past. The echo occurrence,
Doppler velocity, and spectral width of the HF echoes are examined
in order to determine whether new HF echo types are observed at
sub-auroral latitudes, particularly during geomagnetic storms. The
datasets of both TIGER radars are found to be dominated by
low-velocity echoes. A separate population of storm-time echoes is
also identified within the datasets of both radars with most of
these echoes showing similar characteristics to the low-velocity
echo population. The storm-time backscatter observed by the Bruny
Island radar, on the other hand, includes near-range echoes (r<405 km) that exhibit some characteristics of what has been
previously termed the High Aspect angle Irregularity Region (HAIR)
echoes. We show that these echoes appear to be a storm-time
phenomenon and further investigate this population by comparing
their Doppler velocity with the simultaneously measured F- and
E-region irregularity velocities. It is suggested that the
HAIR-like echoes are observed only by HF radars with relatively
poor geometric aspect angles when electron density is low and when
the electric field is particularly high. |
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