| 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 By 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.
The MHD simulations for different constant IMF clock angle cases
show the expected field-line bending and tail twisting for nonzero
IMF By.
The tail becomes longer and at its tailward end stronger twisted for
IMF Bz>∣By∣ than for IMF Bz<∣By∣. 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.
An IMF By sign change causes large deformations of the tail.
After the IMF By 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 By sign change.
Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere
interactions). Space plasma physics (numerical
simulation studies) |