Subject: SOHO/LASCO HALO CME 120920b BACKSIDED

UCMEO 93001 20920 1930/
20920 61512 82006 1022/ 101// 333// 41439
20920 71456 91556 ///// ///// 1112/
99999

PLAIN

SOHO/LASCO observed two (2) HALO CMEs on September 20, 2012.  This alert is
describing the second event [B].  It is first seen in C2 at 15:12 UT as a bright
loop over the Southeast. The loop expands to an asymmetric halo (east) by 15:36 UT.
The event continues into the C3 field beginning 15:30 to 20:06 UT where it leaves
the C3 field at 30 Rsun in the southeast.

Time/height measurements were marked to 3 points in C2 with speeds 
of 1919.2 Km/sec at position angle 134 degrees. The event is marked to 12 points 
in C3. Speeds average through both fields to 1438.9 Km/sec at PA 134 degrees.  
Acceleration -89.23 m/sec^2.

SDO/AIA: 193 shows expanding material behind limb over the east 14:57-15:24 UT.

STEREO: Beacon data
COR2 A, 15:24-15:54 UT in progress at first frame. The LE out to 6Rsun in the SW. The
15:54 UT frame is considered in progress as it is the last frame before a gap period.
Preliminary time/height measure at 2 points gives 2706.7 km/sec velocity at LE. 
EUVI A, 15:05-15:45 UT flare of an AR on the limb with dimming and wave.
COR2 B, 15:25-16:55 UT, asymmetric halo (east).
Preliminary time/height measure at 3 points gives 1932.7 km/sec velocity at LE. 
EUVI B, 14:56-15:56 UT, large flare of the AR in SE quadrant. Event produces a dimming
and a wave over the east.

   
The observation of this event is considered 'GOOD'. This CME is determined a BACKSIDED event.
Due to the size of the wave of material from this type of impulsive burst there may be a small
Earthward factor.

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

http://umbra.nascom.nasa.gov/lasco/observations/halo/2012/120920b

Best regards,

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

BT