Date: Fri, 3 Sep 2004 11:00
From: Guillermo Stenborg
Subject: 'Full' Halo CME on 2004/09/03, backsided...
UCMEO 93001 40903 1500/
40903 60054 80918 0002/ 360// 123// 20412
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PLAIN
BT
LASCO/EIT observed a 'full' halo CME on 2004/09/03. However,
a couple of different events occurred at the time. The 'halo'
event (hereafter Event #1) was first observed in C2 at
00:54 UT all above the SE Limb extending up to the SW Limb as
an 'almost circular' front. Please note that already by
00:30 UT an extremely faint and diffuse front is also seen
surrounding almost completely the C2 occultor. Closer inspection
of its development show that what at first glance seemed only
one front are in fact two: one moving out mainly toward NW (Event
#2), and another one developing mainly toward SE (Event #3).
Starting also at 00:30 UT a ragged feature (brighter than the
other features described above) develops toward WSW - SW
(Event #4), which is followed at 03:06 by a twisted feature.
Also at that time an elongated ragged feature can be seen
developing toward NE (Event #5). The five events are first
seen in C3 by 01:42 UT: Event #1 just barely seen above the
SE Limb, Event #2 (on NW) and #3 (on SE) further out, Event #4
above the WSW Limb as a bright ragged feature, and Event #5
above the NE Limb.
For reference, the mean plane-of-sky speed for the LE of the
different events is shown below (based on C3 data):
Event #1: PA 128 --> 412 km/sec (practically no acceleration)
Event #2: PA 291 --> 484 km/sec (very diffuse LE)
Event #3: PA 086 --> 599 km/sec (very diffuse LE)
Event #4: PA 241 --> 388 km/sec (practically no acceleration)
Event #5: too difficult to track it accurately, but its
speed is in the 350-450 km/sec range.
GOES did not record any significant X-ray activity by the time.
On the other hand, EIT Fe XII images show the lift-off of a
filament located around equatorial latitudes, on the western
hemisphere past half way to the W Limb, starting at around
18:00 UT. This signature is likely to be the EIT counterpart
of either what we called Event #4 or the twisted feature coming
behind. Other than that, there is no other visible signature on
the disk that could be related to the other events mentioned above.
By the time of writing it is not clear whether Events #2 and #3
are related to any of the other two events or are monster of
a different nature.
As for Event #1, it has therefore been determined as a 'full'
halo CME, backsided.
Images and movies of the whole set of events will shortly be
made available at:
ftp://ares.nrl.navy.mil/pub/lasco/halo/20040903a
Please note that by the time of writing another full halo CME
is under development (already in the C3 FOV), first seen in C2 at
10:30 UT. The report will come soon.
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
++