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| Titel |
High time resolution PFISR and optical observations of naturally enhanced ion acoustic lines |
| VerfasserIn |
R. G. Michell, K. A. Lynch, C. J. Heinselman, H. C. Stenbaek-Nielsen |
| 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. 4 ; Nr. 27, no. 4 (2009-04-01), S.1457-1467 |
| Datensatznummer |
250016472
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1457-2009.pdf |
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| Zusammenfassung |
| Observations of naturally enhanced ion acoustic lines (NEIALs) taken with the
Poker Flat Incoherent Scatter Radar (PFISR) using a mode with very high time
resolution are presented. The auroral event took place over Poker Flat,
Alaska on 8 February 2007 at 09:35 UT (~22:00 MLT), and the radar data
are complemented by common-volume high-resolution auroral imaging. The NEIALs
occurred during only one of the standard 15-s integration periods. The
raw data of this time show very intermittent NEIALs which occur only during a
few very short time intervals (≤1 s) within the 15-s period.
The time sampling of the raw data, ~19 ms on average, allows
study of the time development of the NEIALs, though there are indications
that even finer time resolution would be of interest. The analysis is based
on the assumption that the NEIAL returns are the result of Bragg scattering
from ion-acoustic waves that have been enhanced significantly above thermal
levels. The spectra of the raw data indicate that although the up- and
down-shifted shoulders can both become enhanced at the same time, (within 19 ms),
they are most often enhanced individually. The overall power in
the up-and down-shifted shoulders is approximately equal throughout the
event, with the exception of one time, when very large up-shifted power was
observed with no corresponding down-shifted power. This indicates that during
the 480 μs pulse, the strongly enhanced ion-acoustic waves were
only traveling downward and not upward. The exact time that the NEIALs
occurred was when the radar beam was on the boundary of a fast-moving (~10 km/s),
bright auroral structure, as seen in the high resolution
auroral imaging of the magnetic zenith. When viewed with high time
resolution, the occurrence of NEIALs is associated with rapid changes in
auroral luminosity within the radar field of view due to fast-moving auroral
fine structures. |
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