Halo CME Mail

Date: Thu, 16 Aug 2001 17:46

From: Gareth Lawrence

Subject: Full Halo CME on 2001/08/15, backsided

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LASCO observed a bright, fast full halo CME on 2001/08/15. The
leading edge first appeared in the SW at 23:30 UT. This leading
edge filled the SW quadrant by 23:54 and was a full halo CME
in C2 by 00:06, though emission was initially rather faint over
the N Pole. The leading edge was first visible in C3 as a full
halo CME by 00:42. The leading edge passed to the edges of the
C2 and C3 fields of view with mean plane-of-sky speeds of 1200
and 1050 km/s respectively, with a significant deceleration of
some 55 m/s^2.

EIT observed a fairly uniform brightening all around the limb
which we interpret as an EIT wave propagating to the limb from
backsided source. This brightening was first visible at 23:48 UT,
somewhat after the LE first appeared in C2. Given the speed of
the white light CME this timing is consistent with the propagation
of a considerably slower wave to the limb from a distant source
region. Given that the EIT brightening is relatively uniform
and the LASCO CME is quite symmetric it is reasonable to assume
that the source region was close to central meridian; we then
speculate that the source region may have been AR9557, which
crossed the W limb about 5 days prior to this event at a latitude
of about S20. No significant EIT events were discernible on the
frontside and GOES X-ray activity was very low (~B4) and decreasing
during this time.

A proton event commenced shortly after the CME first appeared
in LASCO: energetic particles were clearly visible from about
00:30 and were causing serious degradation of the images by
01:31. Given the quiet conditions on the solar disk during the
entire period, the apparently hard spectrum of the energetic
particles and the presence of energetic electrons it seems
likely that the CME and proton storm were somehow associated,
with a backsided source.

Images and movies of this event are available at:

ftp://ares.nrl.navy.mil/pub/lasco/halo/20010815

Best wishes,
        Gareth Lawrence.
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| 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       |
++