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| Titel |
Bistatic observations of large and small scale ULF waves in SPEAR-induced HF coherent backscatter |
| VerfasserIn |
T. K. Yeoman, L. J. Baddeley, R. S. Dhillon, T. R. Robinson, D. M. Wright |
| 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 ; 26, no. 8 ; Nr. 26, no. 8 (2008-08-05), S.2253-2263 |
| Datensatznummer |
250016184
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2253-2008.pdf |
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| Zusammenfassung |
| HF radar backscatter which has been artificially-induced by a high power RF
facility has been demonstrated to provide ionospheric electric field data of
unprecedented temporal resolution and accuracy. Here such data, induced by
the SPEAR high power radar on Svalbard, are used to investigate ULF wave
processes observed by the CUTLASS HF radars. Observations are presented of
both waves with a large-scale nature, driven externally to the magnetosphere
and those with small azimuthal scale lengths, driven by wave-particle
interactions. For ULF wave events with large azimuthal scale lengths an
excellent agreement in the observed wave polarisation ellipse is found
between the radar observations and ground-based magnetometer data. In
contrast, for the small scale events, no ground-based magnetic counterpart is
observed. Indeed the data from the two CUTLASS radars seem inconsistent, and
each radar must be interpreted separately, as the spatial resolution of the
radars is sufficient to resolve the wave characteristics along the radar
beams, but insufficient to resolve the wave characteristics across the beams.
A high azimuthal wave number (m) wave with a period of 300 s and
m~−60 is observed to occur over Svalbard at ~14:00
magnetic local time. This confirms the existence of waves driven by
wave-particle interactions with trapped particle populations in the outer
magnetosphere. A comparison of the observed wave characteristics with
previous, lower latitude, observations suggests that these high latitude
waves have a similar azimuthal scale size to those generated in the inner
magnetosphere; the azimuthal wave number of −60 observed in the present study
is comparable to previous values of −20– −50, but suggests an increase of
m with latitude. A similar energy source in drifting proton
populations is also suggested, but with lower characteristic proton energies
of 10 keV implicated at high latitude, compared to the 20–60 keV energies
invoked for previous lower latitude observations. |
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