Halo CME Mail Date: Wed, 28 Mar 2001 18:02 From: Gareth Lawrence Subject: Full halo CME on 2001/03/28 ------------------------------------------------------------------------ UCMEO 93001 10328 2330/ 10328 61250 92018 0001/ 360// 113// 4501 10328 61048 91124 22507 09397 1212/ 99999 PLAIN BT LASCO and EIT observed a full halo CME on 2001/03/28. The event was first observed in C2 at 12:50 UT as a bright loop front over the S pole. The C2 occulting disk was surrounded by 13:27 although emission in the most northerly regions was faint. The bright southerly front first appeared in C3 at14:18 with the C3 occultor surrounded by 14:42. The plane of sky speed of the southerly front was measured at 501 km/s at PA 181 (S Pole) with very little deceleration. The probable source of the CME is hard to pinpoint since a great deal of activity was observed by EIT and in X-rays during the preceeding hours. AR's 9393, 9397 and 9402 are all very active during the morning, and there is certainly plenty of activity to give reason to believe that the CME was frontsided. The most likely single event seems to be a system of loops just S of AR 9393 that brighten and move shortly after 11:00 UT, possibly due in some connection to a flare in AR 9397 that peaks in EIT around 10:48. These loops would appear to be the only large dynamical feature on the disk whose motion could be consistent with the first appearance of the CME over the S Pole. Note that the M4 flare in AR 9393, which peaks in X-rays at 12:40 and in EIT at 12:48, does not appear to be the primary source of the CME as the timing is rather late. There is a smaller C9.9 flare in AR 9397 which peaks at 10:47 (10:48 in EIT). Most of the activity seems directed somewhat to the N and W of this region, towards the loops that brighten after. We tentatively identify the loops as the source of the CME and the flare as the source of the loops' instability. Images and movies of this event are available at: ftp://ares.nrl.navy.mil/pub/lasco/halo/20010328 Also, the notification of an earlier backsided halo CME was slightly in error: the easterly front first appeared in C2 at 01:27 rather than 02:27 as previously advised. However this CME is still considered backsided in its origin. There was a degree of activity in AR 9397 between 20 and 23 UT on the previous day, 2001/03/27, but nothing that was considered a probably source for a bright full halo CME. Furthermore, AR 9403 was located some 55 degrees E at the time and the shape of the front around the C2 occulting disk is not consistent with an origin that far fron the central meridian (although this is by no means offered as conclusive proof that the CME was not frontsided). Additionally, if the earlier CME does prove to be frontsided the later CME is likely to catch/overtake/cannibalise it due to its higher speed, rendering the matter more academic. Apologies for a long winded and rather sketchy email! Best wishes, Gareth Lawrence. ++ | Gareth Lawrence, E-mail:grl@ajcannon.nascom.nasa.gov | | SOHO-LASCO Operations Scientist, | | CUA, Mail Code 682.3, | | NASA Goddard Space Flight Center, Phone: +1-301-286-2941 | | Building 26, Room G-1, +1-301-286-3447 | | Greenbelt, MD 20771. Fax: +1-301-286-0264 | ++