Halo CME Mail

Date: Mon, 1 May 2006 14:57

From: Guillermo Stenborg

Subject: Extremely faint Halo on 2006/04/30, frontsided


Status: O

UCMEO 93001 60501 1900/
60430 61034 82118 0001/ 360// 112// 10430
60430 60917 80939 20809 10876 1112/
99999
 
PLAIN


LASCO/EIT observed a couple of frontsided events on 2006/04/30 since early 
in the day. For completeness the description of both events follows, though
is the second event the one more likely geoeffective. In particular:

[1] After a LASCO data gap between 01:31 - 03:54 UT (C2 time) LASCO C2 
images show a bright and ragged loop front already under development
(LE almost at the end of the C2 FOV). Very faint extensions seem to cover 
the C2 occulting disk by 06:06 UT, though it is difficult to say if those 
extension are really associated to the bright loop front event. GOES 
recorded a C5.3 X-ray flare on NOAA AR 10878 (~N16E74) between 
01:33 - 02:07 UT with peak emission at 01:57 UT. There is also an EIT
data gap (between 01:36 - 03:48 UT). Therefore, no signatures of the flare 
could be recorded. However, EIT 195 images do show evidence of a CME under
development on and behind the limb on ENE after the data gap.


[2] An extremely faint and diffuse brightening starts to be discernible 
in C2 above ENE at 10:34 UT, apparently covering the C2 occulting disk 
by 11:54 UT (elliptical shape, i.e., elongated toward E and W). The event 
is barely discernible in C3. A very unreliable determination of its
mean plane-of-sky speed based only in C2 data is as follows (signal too 
faint and diffuse even in C2 to precise the location of the LE):

PA 280: ~360 km/sec
PA 043: ~430 km/sec

GOES recorded a C1.8 X-ray flare on NOAA AR 10876 (S09E08) between 
09:17 - 09:39 UT with peak emission at 09:26 UT. EIT 195 images show a 
brightening between 09:24 and 09:48 UT concentrated in the W part of 
the AR. Some dimming around the filament channel (FC) N and E of AR.


In summary, the event [2] has therefore been determined as an extremely
faint Full Halo Event (only visible in C2), frontsided, associated to a
C-class X-ray event on NOAA AR 10876.

LASCO and EIT movies and images including both events will shortly be 
made available at:

ftp://ares.nrl.navy.mil/pub/lasco/halo/20060430


Best wishes,
	Guillermo Stenborg
  

++
Dr. Guillermo A. Stenborg   
SOHO-LASCO Operations Scientist,                                           
CUA, MC 612.5, 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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