SLOW SHOCKS IN AN OPEN MAGNETIC FIELD NEAR THE SUN

The observed speeds of the coronal mass ejections are often below the estimated Alfven speed but above the sound speed for the background solar corona. This phenomenon suggests that coronal mass ejections may form slow MHD shocks in the corona. This paper presents a numerical study on the formation of the slow shock in an open magnetic field due to the motion of a coronal mass ejection driven by a magnetic flux eruption from below the corona. The slow shock obtained in our numerical model is characterized by a limited latitudinal extent and a slightly flattened shape. It is found that a fast-mode wave always coexists and interacts with the medium ahead of the slow shock. The fast-mode wave deflects the background magnetic field so as to create a rarefaction ahead of the slow shock and a compression in the flank. These effects have a significant influence on the geometry and features of the slow shock.