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| Titel |
Imaging riometer observations of drifting absorption patches in the morning sector |
| VerfasserIn |
R. A. Makarevitch, F. Honary, I. W. McCrea, V. S. C. Howells |
| 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 ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3461-3478 |
| Datensatznummer |
250015024
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3461-2004.pdf |
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| Zusammenfassung |
| Observations by a 7x7-beam imaging riometer in
Kilpisjärvi, Finland (~66° MLAT) of the drifting
cosmic noise absorption (CNA) structures in the morning sector
near the zonal drift reversals are presented. The examination of
the absorption intensity images revealed several regions with
enhanced CNA (absorption patches) slowly drifting through the
riometer field of view (FoV). The absorption patches were found to
vary in shape, orientation (for elongated arc-like patches), and
drift direction. The latter was calculated from the regression
lines to positions of the absorption maxima in the FoV images and
compared with the direction of electrojet plasma flow from
horizontal magnetic perturbations and (for one event) tristatic
ion drift velocities in the F-region. A reasonable agreement was
found between these directions both in point-by-point comparisons
and in terms of direction reversal timings. The absorption patches
of lower intensity appear to have smaller drift velocities and to
be associated with weaker magnetic perturbations. These results
are consistent with the notion that relatively slow motions of the
auroral absorption near the zonal drift reversals are associated
with the drift of the entire magnetic flux tube as opposed to
the gradient-curvature drift of energetic electrons injected into
the ionosphere at the substorm onset. The absorption drift
velocity magnitude, on the other hand, was found to be
substantially lower than that of the plasma flow based on the
results of limited comparison with tristatic ion drift
measurements. A comparison of the drift directions with those of
the patch elongation showed that a considerable number of patches
had these directions close to each other. Using this observation,
we demonstrate a satisfactory agreement between the patch drift
velocities (both in direction and magnitude) as determined from
the absorption images and keograms under the assumption that some
patches were propagating in a direction that was significantly
different from the perpendicularity to elongation. |
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