Date: Thu, 2 Sep 2004 11:12
From: Guillermo Stenborg
Subject: Asymmetric Halo Event on 2004/09/01, most probably backsided
UCMEO 93001 40902 1500/
40901 61538 80018 0002/ 360// 113// 20442
///// ///// ///// ///// ///// /////
99999
PLAIN
BT
LASCO/EIT observed a complex event on 2004/09/01 that showed up
as a very asymmetric halo CME. The event was first observed in
C2 at about 15:38 UT above the WSW Limb as, apparently, two loop
fronts embedded in a diffuse structure. Please note that by that
time EIT was performing the Run #2 of the Shutterless Campaign
(14:00 - 16:40 UT) and therefore there is only about 1 C2 image
per hour (512x512) and no C3 images in that period of time. By
17:50 UT the event developed as a very asymmetric full halo CME
in C2; the leading edge in the SW direction having already left
the C2 FOV, while in the E direction the front is barely above
the C2 occultor. The event was first seen in C3 at 16:38 UT above
the WSW Limb. Please also note that by that time a feature brighter
to N starts developing toward ENE in the C3 FOV, and seems to give
a different appearance to our event. By ~ 00:18 UT on next day the
event is practically no longer visible, apparently without having
reached the end of C3 FOV. The mean plane-of-sky speed for the LE
of the outermost loop front at PA ~ 245 was ~ 442 km/sec. On the
other hand, the inner front showed a plane-of-sky speed of about
400 km/sec at PA ~ 250 (in both cases based only on C3 data).
GOES did not record any significant X-ray activity by the time.
Likewise, the available EIT Fe XII images do not show any signature
on the visible disk. Inspection of the EIT movie made with the
images of the Shutterless sequence do not show anything (in the
restricted FOV) that could be related to our event. See e.g.:
http://umbra.nascom.nasa.gov/eit/movies/shutterless/ems20040901_sless_195.mpg
The event has therefore been determined as an asymmetric 'full'
halo CME, most probably backsided.
Images and movies of the event will shortly be made available at:
ftp://ares.nrl.navy.mil/pub/lasco/halo/20040901
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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