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The IMF Bz used in this simulation. The first hour has Bz=0, the second hour has Bz=-5 nT (southward). The rest of the simulation has Bz=+5 nT (northward). The transitions occur linearly in 2 and 4 minutes, respectively.
Solar wind plasma streamlines (blue), open magnetic field lines (green), closed magnetic field lines (yellow), thermal pressure (rainbow color chart), at t=3900 seconds from the beginning. The simulation began from a dipole in homogeneous cold plasma, with incoming solar wind at x=-32. During t=0..3600 the IMF B was zero but at t=3600 a -5 nT IMF Bz (southward) was switched on. The green box on the nightside magnetosphere is the simulation box of our previous semiglobal simulations. It extends from -20 to -6 in X and 0 to 5 in Z. The radius of the innermost red circle (the inner boundary of MHD) is 3.7 Earth radius. A typical magnetopause shape has been sketched by dark blue line (this line is not taken from the simulation).
An enlargement of the previous slide.
Northern hemisphere ionospheric plane. Noon is up, midnight is down and dusk is left. The color coded quantity is the field-aligned current (FAC), measured positive parallel to background B (which is towards the ionosphere in this case). Thus, red color indicates Region-1 type current (inner ring) on the morningside (right) but Region-2 type current (outer ring) on the eveningside (left). Respectively, blue color indicates Region-2 type current on the morningside but Region-1 type current on the eveningside. The equipotential contours (=plasma streamlines) with 2 kV spacing are displayed as yellow lines. Horizontal current is shown with small arrows. The density is the arrows has been reduced from the actual ionospheric grid point density to make the figure easier to view. The thick turquoise line is the boundary between open and closed magnetic field lines (the separatrix). At this moment (t=3900) in the simulation, the open/closed boundary is expanding because the IMF Bz is southward.
Enlargement of the previous slide.