Geomagnetic storm sudden commencements and their possible sources at the sun

Abstract

We analyze six specific cases of geomagnetic storm sudden commencements (3C's) between 1978 and 1979 with the purpose of determining the events at the Sun which produced them. We use the locations of the solar sources of the shock fronts producing these events as obtained by Hewish and Bravo (1986) by means of the IPS technique. Three of the events had been studied by other authors who attributed them to flares or eruptions of filaments based on their times of occurrence. Information on locations of the sources at the Sun enables us to discard some of these associations and to establish the presence of a coronal hole as the only consistent relation with the source. In three other cases of SC's for which no flare or eruptive filament occur at the disk of the Sun up to five days before the beginning of the geomagnetic storm, we show that a coronal hole was located in the source region of the interplanetary shock that produced the SC. Finally. we discuss the We analyze six specific cases of geomagnetic storm sudden commencements (3C's) between 1978 and 1979 with the purpose of determining the events at the Sun which produced them. We use the locations of the solar sources of the shock fronts producing these events as obtained by Hewish and Bravo (1986) by means of the IPS technique. Three of the events had been studied by other authors who attributed them to flares or eruptions of filaments based on their times of occurrence. Information on locations of the sources at the Sun enables us to discard some of these associations and to establish the presence of a coronal hole as the only consistent relation with the source. In three other cases of SC's for which no flare or eruptive filament occur at the disk of the Sun up to five days before the beginning of the geomagnetic storm, we show that a oronal hole was located in the source region of the interplanetary shock that produced the SC. Finally. we discuss the capability of some kind of coronal hole transients to produce shock fronts travelling in the solar wind and the actual possibility of occurrence of such transients. capability of some kind of coronal hole transients to produce shock fronts travelling in the solar wind and the actual possibility of occurrence of such transients.