Date: Mon, 17 Jan 2005 14:29
From: Guillermo Stenborg Subject: Asymmetric and Complex 'Full' Halo Event, frontsided
UCMEO 93001 50117 1930/
50117 60930 91519 0001/ 360// 123// 32350
50117 60659 81007 42515 10720 1122/
99999
PLAIN
BT
LASCO/EIT observed a 'complex' Full Halo Event on 2005/01/17. The
event was first seen in C2 at 09:30 UT as a very bright loop
front on the NW quadrant surrounded by a very tenuous and diffuse
excess intensity, which in fact, can be guessed (though barely)
in previous frame at 09:06 UT. By 09:54 UT, the LE on NW already
exited the C2 FOV, the occulting disk being completely covered.
Please note that at that time, a new bright and ragged front
appears above the NW Limb. The snowstorm associated with the
proton event reported to start on previous day is still present on
the C2/C3 images, becoming progressively more important (by around
12:30 UT) until making the C2 images completely degraded by 14:07 UT
(14:19 UT for C3).
The event is first seen in C3 at 09:42 UT above the NW Limb. It
is shown as a bright loop front surrounded by a fainter and diffuse
envelope (shock?). The next frame at 10:20 UT shows i) the diffuse
envelope, ii) the loop front, and iii) a much brighter ragged front,
most likely the C3 counterpart of the front appearing in C2 at 09:54 UT.
The C3 occulting disk is completely covered by that time, i.e., at
10:20 UT. The outermost LE of the 'complex' event reaches the end of
the C3 FOV by 11:42 UT.
The mean plane-of-sky speed of the LE of the outermost front of the
diffuse envelope [i.e., feature described as i)] at PA 326 was about
2185 km/sec (as measured on C3 in only 4 frames). On the other hand,
the mean plane-of-sky speed of the apparently fastest outermost feature
belonging to the bright loop [i.e., feature described as iii)] at
PA 263 was 2350 km/sec (based on C3 data, only 4 frames). Given the
superposition of structures during the development of the complex
event, it is difficult to give a reliable value for the speed of
the feature described as ii).
GOES reported a long X-ray duration event on NOAA AR 10720: an X3.8
X-ray flare (N15W25) between 06:59 - 10:07 UT with peak emission
at 09:52 UT, associated to the signatures observed on C2/C3; just
after a compact C3.9 X-ray flare (N15W21) between 06:06 - 06:15 UT
with peak emission at 06:10 UT. EIT 195 images show a steady increase
in intensity on the AR 10720 since around 07:48 UT, peaking at
09:48 UT. Inspection of running differences show an 'intensity peak'
at 08:00 UT followed by expanding loop-like structures toward NW. By
09:36 UT the loops on NW of the AR open and then disappear followed
by a wave to NNE, N, and NW of the AR. Another CME signature can be
seen after 09:48 UT (time of the strongest brightening): wave to NNE,
NW, W, SW, and SSW on disk plus NW, W, SW, SSW off-limb.
In summary, the event has therefore been determined as an asymmetric
and complex 'full' halo event, frontsided.
Movies and images of the event will shortly be made available at:
ftp://ares.nrl.navy.mil/pub/lasco/halo/20050117
NOTE:
Please note that GOES recorded previously two M2-class flares (peak
emissions on 2005/01/16 @ 22:03 UT and on 2005/01/17 @ 03:21 UT).
No clear signatures of associated CME can be seen in C3.
Best wishes,
Guillermo Stenborg
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Dr. Guillermo A. Stenborg
SOHO-LASCO Operations Scientist,
CUA, MC 682.3, Bldg 26, Rm 001, F: +1-301-286-0264
NASA Goddard Space Flight Center,
Greenbelt, MD 20771. P: +1-301-286-2941
e-mail: stenborg@kreutz.nascom.nasa.gov
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