Coronal heating and acceleration of the high/low-speed solar wind by fast/slow MHD shock trains

Abstract

We investigate coronal heating and acceleration of the high- and low-speed solar wind in the open field region by dissipation of fast and slow magnetohydrodynamical (MHD) waves through MHD shocks. Linearly polarized Alfvén (fast MHD) waves and acoustic (slow MHD) waves travelling upwardly along with a magnetic field line eventually form fast switch-on shock trains and hydrodynamical shock trains (N waves) respectively to heat and accelerate the plasma. We determine the one-dimensional structure of the corona from the bottom of the transition region (TR) out to 1 au under the steady-state condition by solving evolutionary equations for the shock amplitudes simultaneously with the momentum and proton/electron energy equations. Our model reproduces the overall trend of the high-speed wind from the polar holes and the low-speed wind from the mid- to low-latitude streamer except the observed hot corona in the streamer. The heating from the slow waves is effective in the low corona to increase the density there, and plays an important role in the formation of the dense low-speed wind. On the other hand, the fast waves can carry a sizable energy to the upper level to heat the outer corona and accelerate the high-speed wind effectively. We also study dependence on field strength, B0, at the bottom of the TR and non-radial expansion of a flow tube, fmax, to find that large B0/fmax ≳ 2 but small B0 ≃ 2 G are favourable for the high-speed wind and that small B0/fmax ≃ 1 is required for the low-speed wind.