Physical and Morphological Properties of CMEs

Russell A. Howard

Abstract

Our understanding of the expulsion of coronal material has improved dramatically since the launch of SOHO.  LASCO has observed small scale outflow in streamers, larger scale ejecta which are the counterpart of the chromospheric surge as well as the large scale coronal mass ejection.  We would like to restrict the definition of a CME to this larger scale process, which appears to be arising from different mechanisms.  We will concentrate on the CME results here and give an overview of our current understanding of CMEs - their physical and morphologic properties.  The kinematic properties are quite similar to previous epochs.  There are some major differences however.  One is in the speed and acceleration profiles.  While the average speeds are about the same as previously, acceleration and even deceleration are observed in a significant number of events. The number of concave outward events is about 1/3 of all LASCO CMEs. These events had been thought to be evidence for disconnection but are now interpreted as "flux rope" events, and are the counterpart of the magnetic clouds seen in the solar wind.  We interpret these flux rope events as eruptions of large-scale streamers overlying a neutral line. Trailing the CME front can be complex small-scale features, which may contain cool material. Utilizing radio emission, we have been able to associate the location of a shock with the leading edge of the CME.

  Authors: R.A. Howard, O.C. St. Cyr, S.P. Plunkett, K.P. Dere, A. Vourlidas

  Organization: NRL
     Telephone: (202) 767-3137
           Fax: (202) 767-5636
        e-mail: howard@cronus.nrl.navy.mil
       Address: Code 7660
   Naval Research Laboratory
   Washington DC 20375