This section briefly presents the results of three other runs with rather different conditions. The purpose of the contrasting runs is to indicate whether or not the results presented in the above subsections may be special to the particular conditions selected for the run.

The run described above was driven by a constant convection electric field imposed at the boundary. We thought it would be of interest to see what happens if there is no convection electric field applied at the boundary, E_y0 = 0. Accordingly, Figure 13 presents the results at t = 28.8 of a run with the same initial conditions shown in Figure 2. The format of the figure is the same as shown in Figures 3-7. Comparison between panel a of Figures 5 and 13 indicates an almost complete collapse of the distant plasma sheet and the onset of some minor reconnection. Keep in mind that this is an almost dissipationless code, so reconnection does not easily occur. However, closer to the Earth conditions are quite similar to the case with finite applied convection. In particular, we still see the expanding region of dipolarization. Panels b and c also indicate that we still get field-aligned current generation that propagates to the high-latitude ionosphere. Panels d and e show considerably diminished flow in the more distant tail, but flow in the nearer tail is nearly the same as for the finite convection case. However, we see a considerably enhanced flow away from the equatorial plane in the expansion region. The pressure plot in panel f shows nowhere near the plasma compression that occurred when the convection electric field was maintained at the boundary. The maximum magnitudes of the B_y and J_|| were about a third less than those shown in Figure 5 with finite E_y.

Another run was initialized with a very thick plasma sheet with a scale thickness of 3R_E, but with the same E_y boundary conditions as the run shown in figures 3-7. Figure 14 shows the initial field lines and the pressure for this run. In this run an attempt was made to balance the field line tension with the earthward pressure gradient. Figure 15 shows the configuration when the run was stopped at t = 36.0. The results should be compared to Figure 6. The field line trace in panel a again shows some thinning. We also see evidence of dipolarization. Panels b and c also show the appearance of field-aligned currents extending to the Earth. The magnitude of the parallel currents and the B_y fluctuations is not much different than the case shown in Figure 6. Panels d and e show the plasma flow. The maximum plasma flow velocity in this case is just somewhat more than a third of the flow maximum in the case shown in Figure 6.

This same configuration was also run with E_y = 0. The results indicated very little flow in the more distant tail. Some flow in the near-Earth region and significantly diminished field line currents connecting to the ionosphere.

Contents

References

Section 4

Section 5