Subject: SOHO/LASCO HALO CME 110321 BACKSIDED

UCMEO 93001 10321 2000/
10321 60224 80742 2922/ 291// 323// 40958
///// ///// ///// ///// ///// /////
99999

PLAIN

SOHO/LASCO observed a HALO CME on March 21, 2011.  Event is first seen in 
C2 at 02:24 UT as a bright loop over the northeast. The impulsive event expands  
with extensions and develops to FULL HALO CME by 03:36 UT with associated material at all
positions. The event is seen in first frame of C3 at 03:06 UT, expanding over the 
northeast and tracked out to 07:42 UT at 29.8 Rsun where material leaves the C3 field.
 
Time/height measurements were marked in C2 to 4 points from 2.7 - 6.4 Rsun with speeds 
of 985.5 km/sec, the event decelerates in C3, marked at 20 points and calculated to
velocities averaging thru both fields to 958.0 Km/sec at position angle 305 degrees
with acceleration -18.5 m/sec^2.    

STEREO EUVI 195A Ahead beacon data has a gap until 04:05 UT then shows a large 
post arcade over an AR in it's NW quadrant which is most likely AR11174 which 
has rotated behind the disk.
STEREO COR2 B shows a large CME from 02:54 - 03:39 UT in it's East field as expected. 
SDO AIA sees a backsided CME in the northeast beginning at 02:14 - 02:49 UT.
There were no Earthward facing events or activity.
   
The observation of this event in LASCO is considered 'GOOD'. This CME is determined a BACKSIDE 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/2011/110321/

Best regards,

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

BT