Two-dimensional magnetohydrodynamic models of the solar corona: Mass loss from the streamer belt

The equations of magnetohydrodynamics (MHD) are used to study an axially symmetric model of the large-scale solar corona, extending from the coronal base to 15 solar radii. We use a uniform heating of the inner corona to investigate the energy output when the magnetic field is given as a dipole at the coronal base. The heat input produces a large-scale magnetic field structure similar to that found by Pneuman and Kopp, with coronal holes in the polar regions and a helmet streamer around the equator. We pay special attention to the energy balance in the system, and find that the role of heat conduction is important in determining the thermal structure in magnetically closed regions. Insufficient energy loss to the transition region leads to a high temperature inside the closed region. In the coronal holes a solar wind is accelerated into interplanetary space, and the temperature is lower. As the difference in pressure scale height along open and closed flux tubes is large, the helmet streamer does not relax to a steady state; it opens periodically to eject mass into interplanetary space. These mass ejections may contribute significantly to the mass and energy flux in the solar wind.