Speaker
Description
The Sun is a star full of charged particles (ions and electrons) everywhere and, as such, behaves as a plasma. The interior and the outer part of its atmosphere (the corona, largely extending into the interplanetary medium) is fully ionized, void of neutral particles. Contrarily, the deeper layers of the solar atmosphere (photosphere and chromosphere) are partly ionized, in which the abundance of neutral particles exceed by a large factor that of charged particles. Despite the large number of neutral particles, the plasma still behaves as a highly-conducting fluid in these layers.
In this talk, the relevant equations governing the evolution of a plasma as a single fluid (interpreted as if a single type of particles were present) will be presented. The main terms in these equations will be interpreted in physical terms and extreme cases with completely different evolutions and properties will be presented, both under a pure academic ideal point of view, as well as with parallel examples in the solar atmosphere. The equations include hydrodynamical terms, as in a neutral fluid, and magnetic terms, derived from the magnetic fields created by the currents generated by the charges and the Lorentz force acting, in turn, on the same particles by those fields. In some situations, the hydrodynamical terms dominate over the magnetic ones, and the plasma evolves and moves as a neutral fluid. In this case, magnetic fields react passively to the motion and evolution of the plasma. This is what happens mostly in the solar interior and in the deep photosphere. From mid-photosphere upwards, the situation changes and the magnetic forces dominate over the hydrodynamical ones. The magnetic field evolves by itself (with the boundary conditions imposed by the field in the underlying layers, because of the continuity of the field lines) and dictates how the plasma particles should behave. In both opposite circumstances, the plasma and magnetic field properties and evolution are completely different.
