November 18, 2010, 12:00 pm - 1:00 pm

November 18, 2010, 12:00 pm - 1:00 pm

High Accuracy Radiative Data from the Iron Pro ject for Solar Opacities

C. G. Fälthammar (Royal Institute of Technology, Sweden)

Although the motion of magnetic field lines in itself is a meaningless concept, it is possible, through an appropriate convention, to define a magnetic field line velocity in such a way that it can be useful. In vacuum electromagnetism, the apparent motion of magnetic field lines has proved to be a valuable tool in teaching electromagnetic theory. In plasma physics, and especially space plasma physics, it has come to be widely used, because it greatly simplifies physical reasoning about plasma physical problems. It is, however, a seductive concept, and already Hannes Alfv�n vigorously warned against its use. The conditions for it to be meaningful are not always satisfied in real plasmas. One requirement is that the Newcomb criterion Bx[B(B.E)/B2]=0 has to be satisfied. This gives a key role to magnetic-field aligned components of the electric field. Such electric field components were long believed to be non-existent in cosmic plasmas, but its is now well established that they play crucial roles in the magnetosphere, for example in the auroral acceleration process and in magnetic reconnection. They can be xpected to exist in many other cosmic plasmas, too. Therefore, if the concept of moving magnetic field lines is used, it has to be with great care.