Expansion of Coronal Mass Ejections within LASCO Field of View: Some Regularities

V.G. Fainshtein

Institute of Solar-Terrestrial Physics (ISTP), Russian Academy of Sciences, Siberian Branch, Irkutsk 33, P.O. Box 291, Russia

As coronal mass ejections (CME) move off the solar surface, they expand; i.e., their linear sizes increase. At present there are only fragmentary data on peculiarities of such CME expansion including those in the field of LASCO coronagraphs. In this paper, CME expansion regularities in the LASCO C2 and C3 field of view are investigated. Forty eight limb CMEs related with near-to-limb eruptive prominences and/or post-eruptive arcades have been tested. It is shown that CMEs can be divided into two groups. The first group includes coronal mass ejections which '2α' latitude angular sizes apparent in the plane of the sky remain unchanged within measurement accuracy of approximately 2-3 degrees. The second one is formed by CMEs that expand 'non-radially', namely, their angular sizes increase by the relative value (10-30)% up to the position of the ejection front RF = Rαm and run to the maximal value 2αm at this distance. It has been found that CMEs of the second type are, on the average, wider, faster and have an outer shell brighter and with higher plasma density for long distances. It is shown that on average Rαm increases as 2αm rises. A weak positive correlation has been found between Rαm and V Flin, where the latter is the CME front velocity derived in the linear approximation of the time dependence of the CME front position. As this takes place, the correlation between Rαm and V Flin becomes higher for CMEs with lower front velocities V F and less values of 2αm.