12-09-2017, 12:00 PM
The three-dimensional image in EUV by the STEREO spacecraft will help to solve projection ambiguities, and observations could be used to configure MHD 3D models of active region loops to study dynamics and stability. Here I present the results of MHD 3D models of active region loops, and progress towards more realistic MHD 3D models of active regions. In particular, the effects of the impulsive events on the excitation of the oscillations of the loops of the active regions and the generation, propagation and reflection of the EIT waves are shown. It shows how 3D MHD models along with 3D EUV observations can be used as a diagnostic tool for active region loop physical parameters, and to advance the science of sources of solar coronal activity.
The lower limit of this simulation is taken from a model of an emergent active region. As a consequence of the emerging magnetic flux and the horizontal motions on the surface, a coronal loop is formed in a self-consistent fashion. We investigate the current density along the magnetic field inside (and outside) of this loop and study the magnetic and plasma properties in and around it. We find that the total current along the loop changes its antiparallel sign parallel to the magnetic field. This is caused by the slope of the loop together with the movement of the reference point. Around the loop, the currents form a complex helical structure free of forces. This is directly related to a bipolar current structure at the loop-through points at the base of the crown and a local reduction of the background magnetic field (ie, outside the loop) caused by the plasma flow along the loop. The locally reduced magnetic pressure in the loop allows the loop to maintain a higher density, which is crucial for extreme UV emission. The performance of the flux in the magnetic field housing the loop is also responsible for the observed collapse of the loop. The complex magnetic field and the surrounding current system can be modeled only in 3D MHD models where the magnetic field has to balance the plasma pressure. A 1D coronal loop model or force-free extrapolation can not capture the current system and the complex interaction of the plasma and magnetic field in the coronal loop, even though the loop is under low conditions.
The lower limit of this simulation is taken from a model of an emergent active region. As a consequence of the emerging magnetic flux and the horizontal motions on the surface, a coronal loop is formed in a self-consistent fashion. We investigate the current density along the magnetic field inside (and outside) of this loop and study the magnetic and plasma properties in and around it. We find that the total current along the loop changes its antiparallel sign parallel to the magnetic field. This is caused by the slope of the loop together with the movement of the reference point. Around the loop, the currents form a complex helical structure free of forces. This is directly related to a bipolar current structure at the loop-through points at the base of the crown and a local reduction of the background magnetic field (ie, outside the loop) caused by the plasma flow along the loop. The locally reduced magnetic pressure in the loop allows the loop to maintain a higher density, which is crucial for extreme UV emission. The performance of the flux in the magnetic field housing the loop is also responsible for the observed collapse of the loop. The complex magnetic field and the surrounding current system can be modeled only in 3D MHD models where the magnetic field has to balance the plasma pressure. A 1D coronal loop model or force-free extrapolation can not capture the current system and the complex interaction of the plasma and magnetic field in the coronal loop, even though the loop is under low conditions.