Coronal mass ejections (CMEs) are important for space weather because they cause large geomagnetic storms. The onsets of CMEs have been associated with both flares and filament eruptions. CME-associated shocks have been studied by Berdichevsky et al. (1998). Much attention has been paid to the study of halo- CMEs (Thompson et al. 1998) because this type of CME is very geoeffective. Much is known about peculiarities of the CME image in different wavelengths (Plunkett et al. 1997) and CME plasmoids (Simnett et al. 1997). However many problems concerning CME origin, connection with large-scale and local solar activity and with other eruptive phenomena are unsolved.
CME onsets in very short time intervals at different position angles on the Sun are at the origin of the multiple CME concept (Lyons et al. 1999). This effect evidences the CMEs globality. It is necessary to continue the work in this direction. This paper devoted to the study of CMEs addresses the question of what part of the solar atmosphere is responsible for their appearance.
The beginning of May, 1998 was characterized by the appearance of proton flares 29.04.98, 02.05.98, 06.05.98, 09.05.98 in NOAA 8210 region. All were followed by CME and shock waves in the interplanetary space (radio bursts II type). The region was localized in the southern hemisphere (S 11-18), but the position angles of CME did not correspond to this hemisphere. The present paper is devoted to the investigation of the coordinates of the CME ejection into the interplanetary space and the activity corresponding to its appearance. The level of global solar activity, which was quite low in this period, was favorable for the identification of the sources. We studied movies obtained from the data of SOHO LASCO C2, C3 coronographs (in white light) and of EIT(195 A) (Delaboudiniere et al. 1995) for the period 24.04-21.05.1998 as well as the activity during this period: subflares, flares, disappearance of filaments, bursts of intensity in the region of 1-8 A (GOES-8). Hundhausen (1997) showed that the bursts of emission in 1-8 A are more closely connected (by their localization and the time of appearance) with CME than optical flares. As was shown by Dryer et al. (1998), the peaks of emission in 1-8 A correspond not only to the instants of flares but also to the instants of CME formation on the solar surface. From this point of view, it is interesting to note that the peaks of this emission are not associated with the appearance of a prominence (Srivastava et al. 1997). Probably GOES 8 did not detect this emission because the site of their origin was not visible (it was on the back side of the Sun). Therefore, we shall assume that if a CME was created but the peak of emission in 1-8 A was absent at the time of its formation (accounting for the fact that our first observations refer to the height above the solar surface), then the region of its formation is localized on the back side of the Sun. For each day of detected CME, we should consider active regions, as the most probable places for the respective perturbation, not only on the visible hemisphere but also the regions that can be localized on the back side of the Sun on this day. Such regions could be both the ones that were detectable 13.5 days later and the regions (although with a less probability) that were registered 13.5 days before the event. The last ones were taken into consideration only in the case of their high activity.
It should also be taken into account that white-light observations can be conducted only for the CMEs whose angles are within 35 degrees with respect to the sky plane (Hundhausen 1993), and their displacements along position angles as projected on the sky plane are insignificant up to 55 degrees latitude. If the initial trajectory of the CME is located in the plane perpendicular to the solar surface, then such a CME should be efficiently observed from the active regions localized not farther than 40 degrees from the limb. Let us introduce now such a position of the ejection plane as an assumption, and let the zone within 40 degrees from the limb be called the favorable one.
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