Date: Mon, 9 Aug 2004 10:41
From: Guillermo Stenborg
Subject: 'Full' halo CME on 2004/08/08, backsided.
UCMEO 93001 40809 1445/
40808 60854 81818 0002/ 360// 233// 30860
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PLAIN
BT
LASCO/EIT observed a 'full' Halo CME on 2004/08/08. However,
several events occurred by the time. The event (# 1) was first
seen in C2 at 08:54 UT as an extremely bright and wide loop front
above the E Limb (with later some trailing material above the NE
Limb). A fainter and diffuse front can be seen ahead of the loop
front spanning from ~ PA 060 - 150. Faint extensions cover the C2
occultor by the time (they happen to be much much fainter above
the NW Limb). Please note that by around 09:06 UT, an elongated
ragged front (# 2) begins to be discernible above the W Limb. By
09:54 UT, a wide ragged loop front can be distinguished on the SW
Limb (# 3), one leg (the brighter one) on SE. A narrower one
follows on SW at 10:34 UT.
The event (# 1) is first seen in C3 at 09:18 UT, above the E Limb,
though faint extensions already surround the C3 occultor. By
09:42 UT (# 2) the elongated loop front appears above the W Limb,
while the ragged loop front (# 3) is clearly distinguished above
the SW Limb at 11:18 UT. For reference, the mean plane-of-sky speed
for Event # 1 at PA ~ 085 was ~ 860 km/sec (outermost edge, based
only on C3 data); for Event # 2: 550 km/sec at PA ~ 262 (cusp of
the loop, also based on C3 data). Please note that the speed of
Event # 2 roughly matches that of the faint extensions at that PA.
EIT Fe XII running difference images show the development of a
backsided CME above the ENE Limb between ~ 08:24 - 10:38 UT.
Faint intensity disturbance traveling to S, above the limb. That
signature is most likely related to the halo itself (Event # 1).
On the other hand, they also show an apparently extremely faint
ejection (barely discernible) a little bit to N of NOAA AR 0655
starting at around 05:48 UT and developing toward W (most likely
related to Event # 2). GOES recorded no significant X-ray activity
by the time that could be directly associated to any of the
individual events mentioned above. However, and for reference,
there was a B3.8 X-ray flare from NOAA AR 0656 (S13E53) between
09:50 - 10:03 UT with peak emission at 09:56.
The event (# 1) has therefore been determined as a 'full' halo CME,
backsided. On the other hand, some ejection likely occurred on the
visible side of the solar disk (Event # 2). Difficult to say more
about Event # 3.
Images and movies of the whole set of events will shortly be
made available at:
ftp://ares.nrl.navy.mil/pub/lasco/halo/20040808
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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