Subject: SOHO/LASCO Partial HALO CME 110509

UCMEO 93001 10510 1730/
10509 62057 80130 3311/ 200// 333// 41252
10509 62025 82045 18917 ///// 1112/
99999

PLAIN

SOHO/LASCO observed a Partial HALO CME on May 09, 2011.  Event is first seen in
C2 at 20:57 UT as a bright loop centered at PA 66 degrees followed by a deep
cavity.  The impulsive front expands with extensions PA 331-200 degrees for a total
coverage of 229 degrees over the East and south hemispheres. The event continues
into the C3 field beginning 21:00 to 01:30 UT out to the edge of view at 30 Rsun.
There is a second event which develops in C2 beginning by 21:48 UT, a faint LE
and slower velocity which is a full halo CME by 23:05-01:25 UT. This second
event may be triggered by the impulsive burst but is fully backsided.

Time/height measurements were marked only 2 points in C2 with speeds of 1345.0 Km/sec
at position angle 69 degrees. The event is marked to 9 points in C3 where it
slightly decelerates.  Speeds average through both fields to 1224.6 Km/sec at
PA 76 degrees.  Acceleration -17.67 m/sec^s.


SDO/AIA shows a flare of AR over the NE limb (currently [N17, E89]) 
beginning 20:42-21:13 UT with a dimming over the East and a sizable wave.         
NOAA reports a long duration C5.4 Xray flare beginning at 20:42-21:19 UT.
STEREO COR2 A & B sees a full halo beginning 21:24 UT.
EUVI B 195 shows AR in the north near central meridian with a flare at
20:25-20:45 UT that produces large scale dimming and wave. 
This is most probably the cause of the Partial HALO event seen in LASCO.

EUVI A 195 shows a small AR eruption in the SW at 20:05 UT with a small dimming/wave.
This may be involved with the second event backsided halo seen in C2.  
   
The observation of this event is considered 'GOOD'. This CME 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/2011/110509/

Best regards,

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

BT