Forward Modeling Method of CME and Discussion About the Projection Modified Method

In this paper, the three-dimension velocity of 21 well-structured Corona Mass Ejections (CMEs) were obtained by Forward Modeling based on STEREO-SECCHI observations during 2007---2008. By measuring the height of the projected front in STEREO-A and STEREO-B sky plane and using the projection modified method, modified velocities of these CME, which were treated as 3D velocity before, were also obtained. Comparing the 3D velocity obtained from the Forward Modeling method and the modified velocity, it is found that the 3D velocity and the modified velocity are almost the same when angular distance, which is defined as the angle between the line connecting CME source region and Sun center and the line connecting observer and Sun center, is greater than 50º; that when the angular distance is less than 50º, the difference is obvious. The latter result shows that the modified method can not be used for the CMEs with angular distance less than 50º. It is found that the projected velocity is almost the same as the 3D velocity when the angular distance is greater than 65º. This result implies that the CME event with angular distance larger than 65º could be treated as a limb event.