日冕物质抛射中非对称高密度云和非线性波的形成和演化

THE FORMATION AND EVOLUTION OF ASYMMETRICAL HIGH DENSITY CLOUD AND NON-LINEAR WAVE IN A CORONAL MASS EJECTION EVENT

应用函数拟合及数字滤波等方法，对ＳＭＭ飞船观测的１９８０年８月１８日日冕物质抛射事件进行了定量分析．论证了不对称高密度云的形成与爆发日珥顶端偏离冕流对称轴有关，讨论了此不对称结构的演化及其对事件发展的影响，作出了暗腔是强磁场膨胀体的重要论断．从图象亮度的高度分布剖面中，分析出日冕非线性波在演化过程中前沿变陡的观测证据，推算了演化成激波的时间和高度，并论证了两者都是强磁场膨胀体所驱动的，而不是瞬时能量爆发所引起的．

The SMM observation of the 18 August 1980 coronal mass ejection is analyzed thoroughly and quantitatively,using the function fitting and digital filtering tech niques.It is shown that the formation of an asymmetrical high density cloud is something related to the deviation in the location of eruptive prominence with respect to the asymmetrical axis of the streamer.The evolution of the asymmetrical structure and its influence on the development of the event are discussed.The dark cavity is proved to be an expanding structure with strong magnetic field. From the radial brightness profiles,the first observational evidence for the front steepening of a non-linear coronal wave during its evolution is found with the time and height for shock formation estimated.The results of the present study are in favor of the event driven by an expanding strong magnetic field structure,rather than by a thermal impulse.