Subject: SOHO/LASCO HALO CME 120920a BACKSIDED

UCMEO 93001 20920 1930/
20920 60548 81130 1022/ 101// 113// 40803
20920 60525 80555 ///// ///// 1122/
99999

PLAIN

SOHO/LASCO observed two (2) halo CMEs on September 20 2012. This alert
is describing the first event [A].  It is first seen in C2 at 05:48 UT
as a faint expanding symmetric halo.
The event continues into the C3 field beginning 06:06 to 11:30 UT
as the cme dissipates in C3 at approximately 21 Rsun.

Time/height measurements were marked to 4 points in C2 with speeds 
of 870.2 Km/sec at position angle 102 degrees. The event is marked to 7 points 
in C3. Speeds average through both fields to 802.7 Km/sec at PA 102 degrees.  
Acceleration -29.39 m/sec^2.

SDO/AIA:  No evidence in 193A.

STEREO: Beacon data
COR2 A, 05:39-06:54 UT as a loop expanding over the southwest hemisphere.
Preliminary time/height measure gives 1266.5 km/sec velocity at LE. 
EUVI A, 05:25-05:55 UT, flare of an AR on the limb in the SW.
COR2 B, 00:00-11:40 UT data gap.  n/a
EUVI B, 00:00-09:26 UT data gap.  n/a

   
The observation of this event is considered 'GOOD'. This CME is determined a BACKSIDED 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/2012/120920a

Best regards,

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

BT