Subject: SOHO/LASCO HALO CME 110924ab

UCMEO 93001 10926 1930/
10924 61248 92118 0791/ 078// 333// 32079
10924 61212 81406 16012 11302 1112/
99999

PLAIN

SOHO/LASCO observed 2 (event A and B) asymmetric HALO CMEs on
September 24, 2011. The event was first seen in C2 at 09:48 UT
with a burst over the east equator which expands.  A second 
impulsive event follows with a bright loop front over the east
at 12:48 UT. The 2 edges are visible in the C3 fields;
event A 09:54-16:42, event B 13:30 (@9.6 Rsun) -21:18 UT.   

Time/height measurements were marked on event B.  Only 2 points
in C2 giving 1050.2 km/sec at PA 79 degrees.  Average through both
fields show 2079.6 km/sec at PA 76 degrees.  


SDO/AIA 193 shows a flare beginning 09:33 - 10:03 UT from AR 11302 in
the NE at [N12, E60]. The flare produced a CME with dimming and wave 
extending over the east and south hemisphere.  Beginning 12:12 UT, a CME
from AR 11302 lifts off before a multi flare triggers at 12:48-14:06 which
produces a wave across the disk, east to west. 
NOAA reports a X1.9 Xray flare of AR 11302 beginning 09:21-09:48 UT and a
M7.1 xray flare of AR 11302 12:33-14:10 UT.

STEREO COR2 B sees these 2 events as asymmetric halos in the field; 09:55
and 12:54 UT with the bulk over the west. 
Time/height measurements from COR2 B beacon data at 5 points with speed of
1441 km/sec at PA 281 degrees.

Time/height measurements from COR2 A beacon data at 5 pts with speed of
1283 km/sec at PA 74 degrees.
 
This is most probably the cause of the HALO events seen in LASCO.
   
The observation of this event is considered 'GOOD'. These are determined a FRONTSIDED events.

Images and movies and time/height information for this event is available on the web at:

http://umbra.nascom.nasa.gov/lasco/observations/halo/2011/110924ab/

Best regards,

Kevin Schenk
Solar Heliospheric Observatory
EIT and LASCO Operations
NASA-Goddard Space Flight Center, USA

BT