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.

磁通量喷发的大气响应Ⅱ.太阳附近的慢激波

日冕物质喷射的观测速度常低于阿尔芬波速的估计值而高于背景日冕声速,这说明日冕物质喷射可能在日冕中形成慢激波。本文取带赤道电流片的冕流结构作为背景,用冕流底部的磁通量喷发作为驱动机制,对日冕物质喷射触发的慢激波进行数值模拟。结果表明,电流片对激波结构有着重要影响。慢激波只出现在电流片的外部,在电流片中逐渐过渡为快激波,慢激波前方的背景磁场在快磁声波的作用下显著偏转,背景密度下降超过10％。慢激波的纬度范围有限,从电流片的外沿大约延伸到±20°,且具有凹向上方的外形。