Time evolution of L_c for simulations G101Dn5In4n3 and G101Dn5In4n4m5 (see the text for the definition). The volume integral is taken over the twisted upper-half magnetosphere in the r–θ plane, with the toroidal integral omitted due to axisymmetry. Specifically, the volume element is ﹩dV={r}^{2}\sin (\theta )drd\theta ﹩. The panels share the same y-axis.