V. Heating and Dynamics of Chromosphere and Corona

Abstract

The crucial role of magnetic fields in any mechanism to heat the outer solar atmosphere has been generally accepted by all authors. However, there is still no agreement about the detailed function of the magnetic field. Heating mechanisms can be divided up into 4 classes: (I) The magnetic field plays a passive role as a suitable medium for the propagation of Alfvén waves from the convection zone into the corona (Ionson, 1984). (II) In closed magnetic structures the slow random shuffling of field lines by convective motions below the surface induces electric currents in the corona which heat it by Joule dissipation (Heyvaerts and Priest, 1984). (Ill) Emerging flux which is generated in the convection zone reacts with ionized material while magnetic field lines move through the chromosphere, transition zone and corona. Rapid field line annihilation, reconnection and drift currents result in heating and material ejection (Brueckner, 1987; Brueckner et al., 1987; Cook et al., 1987). (IV) Acoustic waves which could heat the corona can be guided by magnetic fields. Temperature distribution, wave motions and shock formation are highly dependent on the geometry of the flux tubes (Ulmschneider and Muchmore, 1986; Ulmschneider, Muchmore and Kalkofen, 1987).