Halo CME Mail

Date: Wed, 27 Oct 2004 17:08

From: Guillermo Stenborg

Subject: Complex event on 2004/10/27



UCMEO 93001 41027 2100/
41027 61030 92042 0003/ 360// 123// 10275
///// ///// ///// ///// ///// /222/
99999
 
PLAIN
 
BT 

LASCO observed a complex event on 2004/10/27. The main features
present in the complex event are: i) a wide loop front developing 
mainly toward NE that is first seen in C2 at 10:30 UT above the
ENE Limb, ii) another apparent loop front developing inside the 
previous one, and iii) a much fainter and wider loop front developing
mainly toward S that is first seen in C2 around 12:30 UT as a very 
diffuse front. The feature described in i) is first seen in C3
at 12:42 UT, exhibiting an average plane-of-sky speed in C3 of 
about 275 km/sec at PA 63 deg with practically no acceleration. 
However, that feature shows a slight acceleration while in the 
C2 FOV. By 14:30 UT, the feature spans about 140 deg in C2 (from
PA 340 to PA 120). Afterward, it seems to fully cover the occultor,
having the appearance of a very asymmetric 'full' halo CME, though
it is difficult to be certain due to the superposition with the
feature described in iii). As for the feature in ii), it exhibits an 
average plane-of-sky speed in C3 of about 210 km/sec at PA 65 deg.
As for the feature in iii) it is too faint (barely discernible) in 
C3 to give an accurate value of its plane-of-sky speed. However, a 
value of 312 km/sec at PA 184 was measured.
 
There is report of only one significant X-ray event prior to the 
signatures seen in C2: GOES recorded a C1.1 X-ray flare from the 
NOAA AR 10687 (N09W19) between 05:54 - 06:05 UT with peak emission 
at 05:59 UT. It doesn't seem likely to have any association with 
any of the features seen in C2. But, on the other hand, EIT 195 
images show, starting at about 09:24 UT, what it seems to be a faint
ejection from nearby NOAA AR 0691 (~N15E25) toward S. Moreover, by 
12:00 UT it shows another apparent small ejection from NOAA AR 0689 
(by the time pretty close to the central meridian, North 10). By the 
time of writing it is difficult to say if any of the events seen in 
C2 is related to the apparent ejections seen in EIT.

The event could therefore been determined as a complex, probably
frontsided event, in spite of the temporal correlation observed with 
the EIT 195 images. But honestly, it is hard to be certain.

Movies and images of the event will shortly be made available at: 

ftp://ares.nrl.navy.mil/pub/lasco/halo/20041027


Best wishes,
	Guillermo Stenborg
  

++
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
++