Coronal mass ejection rate and the evolution of the large‐scale K‐coronal density distribution

Abstract

Recently reported occurrence rates of coronal mass ejections (CMEs) are compared with the time scale for the long‐term evolution of the global white light coronal density distribution. This time scale is estimated from the synoptic observations of the corona made from Mauna Loa, Hawaii, by a series of K‐coronameters. The data span a period of more than 20 years and show evolution rates which vary with time roughly in phase with the solar activity cycle. However, there are detailed differences between the sunspot number curve and the long‐term behavior of this quantity. When the occurrence rates of CMEs observed from orbiting coronagraphs, available mainly during the descending phase of the activity cycle, are compared with this evolution time, it is found that the two quantities are inversely proportional. From energy considerations, it is unlikely that there is a causal relationship between CMEs and this coronal evolution. Rather, the result indicates that the processes which lead to the global evolution are intimately related to those which give rise to CMEs, a hypothesis consistent with current theories that CMEs arise from preexisting magnetic structures which become stressed by the global magnetic field rearrangement to the point of instability.