CORONAL HOLES AS SOURCES OF LARGE-SCALE SOLAR-WIND DISTURBANCES AND GEOMAGNETIC PERTURBATIONS

In this paper we present theoretical and observational evidence that low-latitude unstable coronal holes may be, in some circumstances, the source of widespread interplanetary shocks and of the consequent geomagnetic perturbations. We also reanalyze here the shock events tracked by interplanetary scintillation in the study of Hewish and Bravo (1986), which produced the sudden commencement of a geomagnetic storm, in terms of an alternative flare, disappearing filament, or coronal hole eruption origin. The main conclusion of this study is that there are good reasons to consider coronal holes as sources of shock type interplanetary disturbances and that more effort should be made to monitor coronal holes continuously in search of evidence of large short-time changes in their structure and physical conditions.