LASCO Activity Report for
May 27, 2005 SOHO Science Daily Meeting

Event times are first frame seen in C2 camera unless otherwise noted.
These are preliminary observations for the daily SOHO science discussions.
Final analysis is reported on the Lasco CME list.
An archive of these reports is available.

Points Of Interest

* 2005/05/28 - 2005/06/05: LASCO Extra PBs for 3D CME Study.
			   No EIT CME Watch during this period (only synoptic).

* 2005/05/27: EIT CME watch in 304 between 00:00 - 24:00 UT.

* 2005/05/26: EIT CME watch in 304 between 13:34 - 24:00 UT.

* Medoc Campaign started on May 16. Since then SOHO is in Telemetry submode 5
(until June 3 afternoon UT). EIT 195 CME watch at half resolution (512x512).

2005/05/26 (Thursday)

	  N West	Very slow development of a system of faint loops that
			started to be seen by the end of previous day. Some
			small and faint blob-like fronts superposed in the LOS
			(moving faster).

13:27 UT  S West	Diffuse loop front that initially shows up as a fan-
			like front.

15:06 UT  S West	LASCO/EIT observed a full halo event. The event was 
	  (HALO)	first clearly seen in C2 at 15:06 UT all above the SW
			Limb and S Pole. However, a thin brightening just 
			above southern edge of the occulting disk can already 
			be guessed in previous frame (i.e., at 14:50 UT). The 
			event develops in the C2 FOV as a bright, wide, and
			expanding loop front. It superposes in the LOS with 
			the trailing part of a prior (relative narrow) event
			developing on SW (which first appeared in C2 by 13:27
			UT). During its evolution in C2, very faint circular
			extensions can be discerned covering the occulting 
			disk. Our main event is first seen in C3 just appearing
			above the SW Limb at 15:42 UT. By 16:18 UT, faint and
			diffuse circular extensions surround the occulting 
			disk. The plane-of-sky projection of the bulk of the 
			CME develops toward SW. The mean plane-of-sky speed of 
			the event at PA 235 was ~ 575 km/sec, showing a slight
			deceleration (based on C2 and C3 data; last C3 frame 
			at 17:18 UT, LE at ~ 9.5 solar radii). GOES reported
			several B-class X-ray flares on NOAA AR 10767 during 
			the day. In particular, a B7.5 X-ray flare (on ~ S09E15)
			between 13:10 - 15:08 UT with peak emission at 14:20 UT
			(LDE) is most likely associated with the event recorded
			by LASCO. EIT 195 running difference images show by 
			12:36 UT a very faint signature of an apparently
			backsided CME above the SW Limb (EIT 195 counterpart of
			the event first seen in C2 at 13:27 UT, not associated
			with our main event). The EIT 195 CME watch was
			interrupted then at 12:48 UT to start the CME watch 
			in 304 A (JOP 124: Eruptive Filament in Active Region).
			EIT 304 images show the eruption of a backsided
			prominence already above the SW limb at 13:19 UT 
			(EIT 304 counterpart of C2 event at 13:27 UT). Top 
			of post-event arcades visible by 13:36 UT. By 13:48 UT,
			signatures of our main event start to be visible. 
			In particular, material ejected toward SW from nearby 
			AR 10767. In addition, more material (1) shows up 
			above the SW Limb (a little bit to S of the barely
			backside prominence ejection). Inspection of the 304
			movie seems to indicate that the latter (1) could be
			related to the ejection from nearby AR 10767. In 
			summary, the event has therefore been determined as a
			Full Halo Event, frontsided, associated with a LDE
			B-class X-ray flare from AR 10767 and (apparently)
			filament ejection.

21:26 UT  E Limb	Initially faint loop front develops as a wide loop front
			with faint extensions spanning up to the S Pole. By 
			22:26 UT, a very faint and diffuse front can be 
			discerned on ENE, moving apparently faster than the 
			loop just mentioned above (it looks like extremely faint
			circular extensions cover the occulting disk, giving 
			the appearance of a very faint full halo event). This
			front on ENE is followed at 23:26 UT, by a faint and
			ragged loop front. Also by 23:26 UT starts to be
			discernible, above the N Pole, a faint and diffuse 
			loop front. It is difficult to establish the association
			(if any) between the different features observed. They
			all fade throughout C3. GOES recorded a C8.6 X-ray flare
			from NOAA AR 10767 (S08E11) between 20:57 - 22:04 UT 
			with peak emission at 21:39 UT. EIT 304 running
			difference images show a couple of brightenings on AR
			10767 (at 21:13 and 21:36 UT).

2005/05/27 (Friday)

00:50 UT  SS West	Expanding loop front. Note that by 23:50 UT on previous
			day a thin brightening can already be guessed. It is
			followed at 02:26 UT by a narrower front moving
			apparently faster. The event partly superposes in the
			LOS with some small ragged fronts and gusty outflow
			under development on WSW.

06:26 UT  ES East	Ragged loop front followed at 07:26, 08:26, 09:50, and
			11:26 UT by similar (though narrrower) fronts.

08:06 UT  N West	A ragged front develops behind the faint system of 
			loops under development since early on previous day.

08:50 UT  S West	Asymetric (spray-like) loop front. Difficult to give
			an exact time of first appearance.

Time of the last C2 image analyzed: 12:06 UT.