HELMET STREAMERS GONE UNSTABLE: TWO-FLUID MAGNETOHYDRODYNAMIC MODELS OF THE SOLAR CORONA

摘要

The equations of magnetohydrodynamics (MHD) are used to study heating of electrons and protons in an axially symmetric model of the solar corona, extending from the coronal base to 15 solar radii. To study heating of electrons and protons separately, as well as the collisional coupling between the particle species, we use a two-fluid description of the electron-proton plasma. A steady coronal heat input, uniform base pressure, and dipole field boundary conditions produce a magnetic field configuration similar to that seen with white-light coronagraphs during quiet-Sun conditions: a helmet streamer is formed in the inner corona around the equator, surrounded by coronal holes at higher latitudes. The plasma inside the helmet streamer is in hydrostatic equilibrium, while in the coronal holes a transonic solar wind is accelerated along the field. The collisional coupling between electrons and protons becomes weak close to the coronal base. In the case of proton heating, the thermal structure along open and closed field lines is very different, and there is a large pressure jump across the streamer-coronal hole boundary. When the equations are integrated on a long timescale, the helmet streamer becomes unstable, and massive plasmoids are periodically released into the solar wind. These plasmoids contribute significantly to the total mass and energy flux in the solar wind. The mass of the plasmoids is reduced when electrons are heated.