Monitoring magnetosheath-magnetosphere interconnection topology from the aurora
A strong southward rotation of the IMF (B<sub>Z</sub> from 5 to -6 nT in ~ 20 s) on 4 January 1995 caused an abrupt reconfiguration of midday aurorae and plasma convection consisting of the following: (1) the red-line aurora associated with magnetosheath plasma transfer at the lo...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2002-05-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/20/629/2002/angeo-20-629-2002.pdf |
| Summary: | A strong southward
rotation of the IMF (B<sub>Z</sub> from 5 to -6 nT in ~ 20 s) on 4 January 1995
caused an abrupt reconfiguration of midday aurorae and plasma convection
consisting of the following: (1) the red-line aurora associated with
magnetosheath plasma transfer at the low-latitude magnetopause appeared at the
same time that (2) the green-line aurora from precipitating energetic plasma
sheet particles equatorward of the cusp (near the open-closed field line
boundary) weakened visibly and shifted equatorward, (3) the high-latitude
aurora during the previous northward IMF, which is associated with lobe
reconnection, persisted briefly (3 min) and brightened, before it disappeared
from the field-of-view, (4) the activation of a strong convection bay (DPY
current) at cusp and sub-cusp latitudes when the field turned strongly south,
(5) a distinct wave motion of the plasma sheet outer boundary, as inferred from
the aurora, which correlates closely with Pc 5 magnetic pulsations. Our
interpretation of the dramatic reconfiguration is that reconnection poleward of
the cusp coexisted briefly with reconnection at sub-cusp latitudes. The latter
provided a magnetic field connection which enabled, on the one hand,
magnetosheath particles to enter and cause the red-line cusp aurora, and on the
other hand, allowed for magnetospheric energetic particles to escape and weaken
the outer plasma sheet source of the green-line emission. The coexistence of
the two cusp auroras reflects the time required for one field line topology to
replace another, which, under the prevailing high speed wind ( ~ 650 km/s),
lasts ~ 3–4 min. The motion of open flux tubes propagating from equator to
pole during this transition is traced in the aurora by a poleward moving form.
The waves on the outer boundary of the plasma sheet are most likely due to the
Kelvin-Helmholtz instability. The study illustrates the ability of local
auroral observations to monitor even a global change in magnetospheric magnetic
topology.<br><br><b>Key words. </b>Magnetospheric Physics (auroral
phenomena; magnetopause, cusp, and boundary layers; solar wind-magnethoshere
interactions) |
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| ISSN: | 0992-7689 1432-0576 |