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Ann. Geophys., 21, 2303-2314, 2003
www.ann-geophys.net/21/2303/2003/
© European Geosciences Union 2003
Pre-noon high-latitude auroral arcs as a manifestation of the interchange instability
A. E. Kozlovsky1,2, V. V. Safargaleev3, J. R. T. Jussila2, and A. V. Koustov4
1Sodankylä Geophysical Observatory, Sodankylä, FIN-99600, Finland
2Department of Physical Sciences, University of Oulu, Oulu, FIN-90014, Finland
3Polar Geophysical Institute, Apatity, 184200, Russia
4Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
Abstract. On 7 December 2000, TV ASC camera in Barentsburg (Svalbard)
observed pre-noon (at 09:00–10:00 MLT) rayed auroral arcs, which occurred at
the pole-ward edge of the auroral oval after an IMF transition from By
-dominated (By = + 8.8, Bz = + 4.3) to strongly
northward dominated (By = +
2.7, Bz = + 8.6). The arcs appeared from the area of enhanced luminosity seen
in the western (nightside) horizon, and developed to the east, progressing at a
velocity of about 1.5 km/s. Simultaneously, the arcs were drifting poleward at
a velocity of 300–500 m/s, whose value was equal to the F-region ionospheric
plasma drift velocity observed by the Incoherent Scatter Radar (ESR). The arc
appearance and motion corresponded well to the poleward expansion of the
auroral oval following the IMF shift, which was observed by the UVI on board
the Polar satellite. The observed auroras were associated with closed LLBL
indicated by the particle precipitation data from DMSP satellites showing also
several-keV electrons of PS origin. The observations allow us to suggest that
the arcs arise due to the interchange instability that starts to develop at the
boundary between the magnetospheric plasma and the magnetosheath flux tubes
entering the closed magnetosphere due to the reconnection beyond the cusp after
the IMF changes. The interchange instability can be suggested as a possible
mechanism for the formation of the LLBL.
Key words. Magnetospheric physics (auroral phenomena;
magnetopause, cusp and boundary layers; magnetospheric configuration and
dynamics)
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