Subject: SOHO/LASCO HALO CME 120123ab

UCMEO 93001 20123 1730/
20123 70412 90530 3291/ 328// 333// 32102
20123 60200 80442 42029 11402 1112/
99999

PLAIN

SOHO/LASCO observed a full asymmetric HALO CME on January 23, 2012. This appears as
2 halo events in close succession.  Event is first seen in C2 at 04:12 UT as a bright 
halo over the north hemisphere in progress with LE at 5.8 Rsun.  The first event with
slightly fainter LE is noticeable by the extending flanks.  The second event has overtaken  
in the first frame of lasco data coming out of a temporary data gap at this time.  The second
event is also an asymmetric HALO with deep cavity and bright core material.
The event continues into the C3 field beginning 04:18 to 05:30 UT at another data gap with
LE to 19 Rsun.  Proton emission is seen in the white light images.

Time/height measurements were marked in 2 separate positions due to data gaps.
On the flanks which are the first event, 5 points in C2 with speeds of 868.7 Km/sec
at position angle 231 degrees. The event is marked to 4 points in C3. Speeds average
through both fields to 860.5 Km/sec at PA 232 degrees.  Acceleration -90.13 m/sec^s.
The second measure was taken at the upper LE on the impulsive front.  Marked at only
1 pt in C2 and 7 pts in C3, the event averages through both fields 2102.2 Km/sec
at pa 329. Acceleration of 94.84 m/sec/^2.  These speeds can be updated with the
recovered data gaps. 


SDO/AIA shows a dimming/cme beginning 02:00-02:57 UT from AR 11402 in the NW quadrant
located at [N29, W20]. At 03:09 UT a second emission begins prior to a long duration
flare of AR 11402 03:39-04:42 UT producing a northward directional wave and post arcade. 

NOAA reports a long duration M8.7 Xray flare beginning 03:38-04:34 UT from AR 11402.
Proton flux at >50 MeV is reported above Storm Levels with increased 100 MeV flux.

STEREO: Beacon data
COR2 B,  03:55-05:40 UT.  In progress at 5.4 Rsun, full asymmetric halo over the west. 
Preliminary time/height measure gives 1466.3 km/sec velocity at LE.
EUVI B, 02:16-02:56 UT CME over NW limb, 03:46-04:42 UT CME with wave and bright post
loops.
COR2 A, 23:24-05:42 UT data gap. Event in progress at edge of field LE, full asymmetric
halo over east
EUVI A, 23:15-05:25 UT data gap. In progress on limb in NE with bright post loop arcade.

   
The observation of this event is considered 'FAIR'. 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/2012/120123ab/

Best regards,

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

BT