标题： 不稳定的日冕环：具有预测观测特征的数值模拟 显示英文标题

标题： Unstable coronal loops : numerical simulations with predicted observational signatures

摘要： 我们对日冕环的非线性、电阻磁流体动力学（MHD）演化进行了数值研究。 对于这些模拟，我们假设环不携带净电流，这可能是由于环通过涡旋流演化而产生的预期结果。 此外，初始平衡被设定为具有线固定端的圆柱形通量管。 对于给定的磁场扭转变量，众所周知，一旦这样的环超过临界长度，就会变得对理想MHD不稳定性不稳定。 这些不稳定性早期演化会产生大的电流集中。 首先，我们表明这些电流集中与电流片的形成是一致的。 磁重联只能在这些电流集中的附近发生，因此我们将电阻率与局部电流密度耦合。 这样做的优点是避免了在应该可以忽略的区域出现电阻扩散。 我们通过与基于均匀电阻率的模拟比较，展示了这一过程的重要性。 从我们的数值实验中，我们可以估计不稳定日冕环的一些观测特征。 这些特征包括：环变亮的时间尺度；温度的增加；释放的能量以及预测的可观测流动速度。 最后，我们讨论这些观测特征在多大程度上与瞬时明亮环的特性一致。 显示英文摘要

摘要： We present numerical studies of the nonlinear, resistive magnetohydrodynamic (MHD) evolution of coronal loops. For these simulations we assume that the loops carry no net current, as might be expected if the loop had evolved due to vortex flows. Furthermore the initial equilibrium is taken to be a cylindrical flux tube with line-tied ends. For a given amount of twist in the magnetic field it is well known that once such a loop exceeds a critical length it becomes unstableto ideal MHD instabilities. The early evolution of these instabilities generates large current concentrations. Firstly we show that these current concentrations are consistent with the formation of a current sheet. Magnetic reconnection can only occur in the vicinity of these current concentrations and we therefore couple the resistivity to the local current density. This has the advantage of avoiding resistive diffusion in regions where it should be negligible. We demonstrate the importance of this procedure by comparison with simulations based on a uniform resistivity. From our numerical experiments we are able to estimate some observational signatures for unstable coronal loops. These signatures include: the timescale of the loop brightening; the temperature increase; the energy released and the predicted observable flow speeds. Finally we discuss to what extent these observational signatures are consistent with the properties of transient brightening loops.