两冕流间的对称径向膨胀日冕物质抛射事件

本文讨论了发生在冕流对之间的１９８０年５月６日日冕物质抛射事件，提出了一种描述事件外环运动的经验模型，把环的观测外形表达为在运动坐标系中的Ｃａｓｓｉｎｉ函数，环的发展过程分为两个阶段：在前一阶段，外环外于冕流对盔状结构之间，事件的发展以角宽度膨胀为主，其对称轴从赤道向北纬方向移动；径向膨胀和上升速度较低，加速效应明显，在后一阶段，外环越过冕流盔状结构所在高度，角膨胀趋于停止；运动接近于等角宽度和纯

RADIAL EXPANSION OF A SYMMETRICAL CME BETWEEN TWO CORONAL STREAMERS

The CME event on May 6,1980,occurring between a pair of coronal streamers,is discussed in this paper.An empirical kinematical model is proposed for describing the motion of outer loop of the event,n which the observed profile of loop is fitted in terms of the Cassini function in a moving coordinate system.The development of the loop can be distinguished into two different phases.During the first phase,when the loop lay between the helmet structures of streamer pair,the development of event is dominated by expansion of angular width with the asymmetrical axis shifting to northern latitudes;the speed of radial expansion and outward motion were rather low with remarkable acceleration.During the second phase,when the outer loop moved beyond the height of helmet structure of coronal streamer,the angular expansion ceased;the motion approached to an expansion and lift mainly in the radial direction with uniform speed and invariable angular width.As the loop moved outward,both the top and center heights increased with time, however,the bottom remained nearly fixed.Based on the above observational characteristics,a possible mechanism is put forward for the formation of the event.