In this section, we take a closer look at the evolution of the plasma sheet during the course of the simulation. Figures 8 a-d show line cuts? spatial profiles along z of the x-component of the magnetic field, the plasma density, the perpendicular and parallel pressures, and , and the x-component of the plasma flow velocity.

Figure 8a shows the initial state, while Figure 8b shows the ‘growth phase’ state at t = 14.4 and x = -9 R_E, -12 R_E, -15 R_E, and -18 R_E. At x = -9 R_E, the buildup of the particle density, pressure, particularly the parallel pressure and increased earthward flow indicate that plasma injection is occurring. The cross-tail gradient in gradient B_x also seems to have broadened considerably. The same situation appears true at x = -12 R_E. However, at x = -15 and -18 R_E, there is some sharpening of the gradient in B and peaking in , while the width of the remains broad and fairly well matches the shape of the velocity profile, except at the center.

Figure 8c shows the profiles at the beginning of the ‘expansion’ phase at t = 28.8. The profiles at x = -9 and 12 R_E appear to be engulfed in the expansion region. It is worth mentioning that the profiles of V_y and B_y (not shown) show large amplitude fluctuations. However, at x = -15 and -18 R_E, the gradient in B_x shows considerable steepening accompanied by a sharp peak in . on the other hand remains double-humped with skirts that fairly well match V_x the profile.

Finally, by t = 36.0, shown in Figure 8d the expansion of the dipolarization can be seen to have reached as far as x = -15R_E. This is also accompanied by large fluctuations in V_y and B_y. However x = -18R_E is clearly beyond the expansion region. Here we see a continued sharpening of the gradient in B_x and peaking of the profile, while the profile is double humped with the wings matching the V_x profile. Through all of this there is no particularly large change in the density profile tailward of the dipolarization region.

Contents

References

Section 4

Section 5