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| Titel |
Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images |
| VerfasserIn |
N. C. Maynard, J. Moen, W. J. Burke, Mark Lester, D. M. Ober, J. D. Scudder, K. D. Siebert, D. R. Weimer, C. T. Russell, A. Balogh |
| 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. 8 ; Nr. 22, no. 8 (2004-09-07), S.2917-2942 |
| Datensatznummer |
250014975
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| Publikation (Nr.) |
 copernicus.org/angeo-22-2917-2004.pdf |
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| Zusammenfassung |
| We demonstrate that high-resolution 557.7-nm all-sky images are useful tools
for investigating the spatial and temporal evolution of merging on the
dayside magnetopause. Analysis of ground and satellite measurements leads us
to conclude that high-latitude merging events can occur at multiple sites
simultaneously and vary asynchronously on time scales of 30s to 3min.
Variations of 557.7nm emissions were observed at a 10s cadence at
Ny-Ålesund on 19 December 2001, while significant changes in the IMF
clock angle were reaching the magnetopause. The optical patterns are
consistent with a scenario in which merging occurs around the rim of the
high-latitude cusp at positions dictated by the IMF clock angle. Electrons
energized at merging sites represent plausible sources for 557.7nm emissions
in the cusp. Polar observations at the magnetopause have directly linked
enhanced fluxes of ≥0.5keV electrons with merging. Spectra of
electrons responsible for some of the emissions, measured during a DMSP F15
overflight, exhibit "inverted-V" features, indicating further acceleration
above the ionosphere. SuperDARN spectral width boundaries, characteristic of
open-closed field line transitions, are located at the equatorward edge of
the 557.7nm emissions. Optical data suggest that with IMF BY>0, the
Northern Hemisphere cusp divides into three source regions. When the IMF
clock angle was ~150° structured 557.7-nm emissions came from
east of the 13:00 MLT meridian. At larger clock angles the emissions appeared
between 12:00 and 13:00 MLT. No significant 557.7-nm emissions were detected in
the prenoon MLT sector. MHD simulations corroborate our scenario, showing
that with the observed large dipole-tilt and IMF clock angles, merging sites
develop near the front and eastern portions of the high-altitude cusp rim in
the Northern Hemisphere and near the western part of the cusp rim in the
Southern Hemisphere. |
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