Halo CME Mail

Date: Wed, 28 Mar 2001 18:02

From: Gareth Lawrence

Subject: Full halo CME on 2001/03/28


Status: O

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       |
++