Coronal heating and the solar mass loss processes above the open field region

Takuma Matsumoto, Nagoya University, Japan

The mass loss rate from the sun is determined by the coronal temperature and density. To determine the coronal temperature and density is one of the main purposes in so-called coronal heating problem. According to the classical atmospheric model of the sun, only a small fraction of the kinetic energy of the surface convection motion is necessary to maintain the hot corona. The coupling between the convection and the magnetic field produces upward Poynting flux that deposits the magnetic energy to the ambient plasma through various kinds of mechanisms. To specify the transportation and the dissipation processes of the magnetic energy must give us intriguing clues to solve the coronal heating problem.

Since the solar atmosphere is significantly inhomogeneous due to the gravity and the magnetic field, the transport and the dissipation processes will inevitably include nonlinear processes. While a lot of elemental theories that treat only the portion of the global atmosphere have been developed, the number of comprehensive theories that can predict the coronal temperature, density, and the mass loss rate remains very small for now. In accordance with the above situation, we have performed 2.5D magneto-hydrodynamic numerical experiments of the solar atmosphere to determine the mass loss rate. We will treat a single magnetic flux tube extended from a strong magnetic field (kG patch), expanding super-radially near the surface. As an energy injection processes, we consider Alfven wave at the foot point of the flux tube. The main purpose of this talk is to specify the transport and the dissipation processes of Alfven wave in this simple 2.5D MHD systems.

Our numerical system acquires a quasi-steady state with hot corona and high-speed solar wind whose mass loss rate is comparable to the current sun. The dissipation of Alfven wave turned out to have different mechanisms in each height. Below the transition region, the heating associated with nonlinear mode conversion is dominant as is also found in 1.5D simulation. In addition to the mode conversion, strong refraction combined with the phase mixing contributes to the plasma heating just above the transition region. Above 0.2-0.3 Rs from the photosphere, MHD turbulence starts to develop and plays a dominant role in the plasma heating that balance to thermal conduction loss. Since the refraction and the turbulence do not occur in 1D model, our numerical experiments show that the deviation from the 1D model increases with height. In this talk, I will introduce the details of our model and what happens in our numerical experiments.