Date: Wed, 19 Sep 2001 16:54
From: Gareth Lawrence
Subject: Full Halo CME on 2001/09/18, most probably backsided
Status: O
LASCO observed a full halo CME on 2001/09/18. The event was first
just observed in C2 at 20:30 UT as a very narrow bright front
in the SW. By 21:30 UT this front completely surrounded the
C2 occulting disk. The front first appeared in C3 at 21:18 UT
with full coverage of the C3 occultor by 22:18 UT.
At the time of the event EIT was observing in 171 A rather than
the usual 195 A, a wavelength less well-suited to CME observations.
However, activity on the disk was minimal at the time, which is
reflected in the GOES X-ray data around the time. There is a
small, rapid transient brightening/ejecta seen in EIT at 19:48
just to the W of AR9616 at S12W15, which could correlate with
the CME in both time and location. However, it is highly unlikely
that such a small event would lead to such a fast, bright CME
with complex prolonged outflow such as is seen in the SW. There
is no evidence of any disappearing filaments of any significance.
Therefore, mindful of both the limitations of the 171 A data
and the familiarity of the observer with this dataset, we
identify this CME as backsided. In addition, if this event
were in fact frontsided, it would be likely to catch up and
interact with an earlier frontsided CME.
For reference, images and movies of this event are available at:
ftp://ares.nrl.navy.mil/pub/lasco/halo/20010918b
and one of the C3 movies shows the interaction with the previous
event.
Best wishes,
Gareth Lawrence.
++
| Gareth Lawrence, E-mail:grl@kreutz.nascom.nasa.gov |
| SOHO-LASCO Operations Scientist, |
| CUA, Mail Code 682.3, |
| NASA Goddard Space Flight Center, Phone: +1-301-286-2941 |
| Building 26, Room G-1, +1-301-286-3447 |
| Greenbelt, MD 20771. Fax: +1-301-286-0264 |
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