Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study
We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF <i>B<sub>y</sub></i> sign change during northward...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2004-03-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/22/951/2004/angeo-22-951-2004.pdf |
| Summary: | We investigate with the help of a magnetohydrodynamic (MHD) model how the
large-scale
topology of the magnetosphere develops for a constant interplanetary
magnetic field (IMF) with different
IMF clock angles and for an IMF <i>B<sub>y</sub></i> sign change during northward IMF.
A detailed examination of the topological changes in the tail and the
ionosphere for different IMF conditions shows a good agreement with
observational results.
</p><p style="line-height: 20px;">
The MHD simulations for different constant IMF clock angle cases
show the expected field-line bending and tail twisting for nonzero
IMF <i>B<sub>y</sub></i>.
The tail becomes longer and at its tailward end stronger twisted for
IMF <i>B<sub>z</sub></i>>∣<i>B<sub>y</sub></i>∣ than for IMF <i>B<sub>z</sub></i><∣<i>B<sub>y</sub></i>∣. The field
lines originating in the high-latitude flank of the far-tail plasma
sheet map into the near-Earth tail lobes and to a strongly poleward
displaced polar cap boundary. A comparison with observations suggests
that an oval-aligned arc may occur on the high-latitude part of the
polar cap boundary.
</p><p style="line-height: 20px;">
An IMF <i>B<sub>y</sub></i> sign change causes large deformations of the tail.
After the IMF <i>B<sub>y</sub></i> flip the near-Earth and far-tail plasma sheet
regions are oppositely twisted which causes in the near-Earth tail a
bifurcation of the closed field line region that moves from one flank to
the other.
The bifurcated part of the closed field line region maps to a bridge
of closed field lines moving over the entire polar cap. This moving
bridge may be interpreted as the mapped region of a moving
transpolar arc. Based on earlier observations, such a type of polar
arcs is expected to occur after an IMF <i>B<sub>y</sub></i> sign change.<br><br>
<b>Key words. </b>Ionosphere (auroral ionosphere; ionospheremagnetosphere
interactions). Space plasma physics (numerical
simulation studies) |
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| ISSN: | 0992-7689 1432-0576 |