The Search for CME Onsets

The four image sets of this movie show a 4x12 arcminute field of the northeast solar limb from 13:23 to 22:19 UT on February 4, 2001, in He I 584 Angstrom, O V 629 Angstrom, Mg IX 368 Angstrom and Fe XVI 360 Angstrom, characteristic of 20,000 K, 250,000 K, 1 million K and 2 million K. The images are taken at the same time and place. Such sequences are used to look for the onset signatures of CMEs. The sequence shows much activity and structure. An active region in the middle of the image field shows enhanced high temperature emission and shows an extremely active and variable loop which is particularly clear in the O V line. The same region is the northern extreme of a system of loops which appear to extend below the equator to another active region on the southern extreme of the field. Despite the activity, no clear eruption is observed in the EUV. However, for the same period, the LASCO coronagraph data displayed three events, observed from 15:30, 16:06 and 17:54 UT all over the east and northeast limb. The drama of the CME events in the high corona is not reflected in the subtle effects of the low corona. To identify evidence for an eruption in the EUV, especially when there is no prominence material involved in the eruption, requires a careful analysis of the EUV emission lines to identify, for example, dimming as material is extracted.