CME速度的投影效应改正方法

目前观测得到的日冕物质抛射(coronal mass ejection,CME)只是其在天空平面的投影,其观测参量与真实参量之间存在一定的差异.而CME的速度是对其地磁效应有决定性影响的参量,因此对CME测量速度作投影效应改正是一个重要的研究课题.综述了近年来对CME测量速度进行投影效应改正的方法,并指出了这些投影效应改正方法中存在的一些问题和进一步的研究方向.

The Methods of Correcting the Projection Effects on the CME Velocity

Coronal mass ejections(CMEs),known as the most energetic form of solar magnetic activity,are now believed to be the main sources of the strong interplanetary disturbances that cause moderate to intense geomagnetic storms.Since CMEs were first discovered on Dec 14 1971 by using the seventh Orbiting Solar Observatory(OSO-7)coronagraph,they have drawn more and more attention. Several space-borne coronagraphs and ground-based instruments have found a number of CMEs, which give a good chance to study them in details. However, coronagraph observations of CMEs are subject to the projection effects, which result in statistical errors in the eruption velocity and acceleration measurements. The sky-plane projected velocity of CMEs perceived as a quantitatively accurate measurement may compromise the value of scientific studies, thus the study on the methods for correction projections of CMEs velocities on the sky-plane is an important topic.In this paper, the recent methods for correction the sky-plane projected velocity are re-viewed and further the uncertainties of these methods are pointed out. The major methods are summarized as follows: (1) CMEs' evolution models dependent, e.g. different CME cone mod-els; (2) CMEs' propagation properties dependent, in which CMEs are assumed to move radially,sometimes to maintain a constant angular width, and so on; (3) CMEs' source region dependent.Concerning this item, CME source region is sometimes determined to be the point that has the shortest distance or spherical distance to the associated surface event. Sometimes the central po-sition angle (CPA) of a CME was converted to its latitude, and its longitude is obtained from the associated surface event. The uncertainties in these methods are mainly from simplified assump-tions on CME structures; propagation properties and source regions on direct 3-D observations.It is expected that 3-D observations by the STEREO should solve this problem.