Subject: SOHO/LASCO HALO CME 120423

UCMEO 93001 20424 2030/
20423 61848 90454 0951/ 265// 223// 30406
20423 61736 81815 42012 11461 1112/
99999

PLAIN

SOHO/LASCO observed a HALO CME on April 23, 2012.  Event is first
seen in C2 at 18:48 UT as faint loop(s) expanding over the South and East
hemispheres.  Halo appears as a multi-loop event. The event continues into
the C3 field beginning 19:06 to 04:54 UT where it dissipates at 21 Rsun in
the South.  We are focusing on the leading loop system over the South.

Time/height measurements were marked to 5 points in C2 with speeds
measuring 588.1 km/sec at position angle 195 degrees. 
The event is marked to 13 points in C3. Speeds average through both fields
to 405.5 Km/sec at PA 189 degrees.  Acceleration -17.90 m/sec^2.


SDO/AIA 193 shows a large loop CME over the limb in the west at 16:42 UT.
Beginning 17:36-18:15 UT a flare of AR 11461 located [N12,W20] erupts producing
a wave southward.  

STEREO: Beacon data
COR2 A, First seen at 18:24 UT, a bright burst expanding SE.
Preliminary time/height measure gives 1016.6 km/sec velocity at LE. 
EUVI A, A flare with cme 16:36-17:15 UT from AR on disk near disk center.
Beginning 17:35-18:15 a large cme on limb in the east.
COR2 B, an expanding burst over the SW beginning at 18:24 UT.
Preliminary time/height measure gives 999.4 km/sec velocity at LE.
EUVI B, a large wave seen from over the limb in the east at 16:45 UT.

NOAA reports a C2.0 Xray flare of AR 11461 17:38-18:05 UT.
   
The observation of this event is considered 'FAIR'. Two events produce a full halo
in C2.  The partial halo with width of 170 degrees over the south is determined
a FRONTSIDED event. 

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

http://umbra.nascom.nasa.gov/lasco/observations/halo/2012/120423/

Best regards,

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

BT