tokens: is no longer achieved and no solutions are found. (For more details on the Grad–Shafranov solver, refer to Paper I .) 3 RESULTS We next present results from various runs for the magnetosphere, as it adapts to the internal evolution. In the leftmost panel of Fig. 1 , we show the 2D projection of the magnetic field lines (on the r θ plane) at several snapshots throughout the evolution of the sample field defined as model A in Section 2.2 . In this case, the initial field is dipolar, with a toroidal component of relative strength , confined within the critical field line defined by P c = 0.5 P o . Crucially, a value of P c P o allows for a toroidal field to be present in the magnetosphere at the start of our simulation. Figure 1. Left-hand panel: snapshots of the projection of field lines in the meridional plane for model A at three different times: the initial field configuration at t = 0 is shown with dotted lines; the field at t = 1500 yr is shown with dot–dashed lines; and the field at t = 1579 yr (the last time-step before the magnetosphere saturates) is shown in solid lines. The star is shown in grey, and the distances are rescaled by the stellar radius. The critical field line at t = 1579 yr (confining the magnetospheric currents) is shown thicker. Note the accelerating expansion of the field lines over the last two snapshots. Middle and right-hand panels: 3D field lines for the initial magnetic field (at t = 0) and for the last snapshot before reaching the critical point (at t = 1579 yr), respectively. We find that, starting with an initial toroidal field occupying part of the magnetosphere, it gradually increases in amplitude over the course of the evolution. Consequently, the strength of magnetospheric currents, total energy, helicity and twist in the magnetosphere steadily increase over time, and the field lines stretch outwards as the simulation progresses. This continues until the toroidal field reaches a maximal amplitude, beyond which simple field configurations with lines connected to the interior are no longer feasible solutions of the Grad–Shafranov equation (see Paper I ), and thus the magnetosphere reaches what we refer to as a critical point . For the particular model presented here, this happens at approximately t max ≈ 1579 yr. It is important to notice that t max is not very sensitive to the exact twist at which the reconnection event occurs because, once the twist is significant (∼1 rad), the evolution proceeds very rapidly. At this moment, we expect the magnetosphere to undergo a violent rearrangement on the Alfvén time-scale, resulting in the expulsion of some or all of the excess energy stored in the toroidal component. After this rearrangement, the evolution will continue, starting from the new initial state, and the process is repeated. Thus, one would expect recurrent outbursts or flares throughout the evolution, each resulting in the expulsion of a fraction of the available energy. The amount of energy
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