LASCO Activity Report for
September 07, 2004 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

2004/09/03 (Friday)

00:30 UT  NW    Extremely faint and diffuse front surrounding almost the C2
		occultor. SEE description of event reported to start at 00:40 UT.

00:30 UT  WSW	Bright ragged feature. SEE description of event reported to 
		start at 00:40 UT.

00:40 UT  SE	Almost circular front develops as a 'full' halo CME. The 'halo'
        (HALO)	event (hereafter Event #1) was first observed in C2 above the 
		SE Limb extending up to the SW Limb. Please note that already 
		by 00:30 UT an extremely faint and diffuse front is also seen
		surrounding almost completely the C2 occultor. Closer inspection
		of the development of this faint front shows that what at first
		glance seemed only one front are in fact two: one moving out
		mainly toward NW (Event #2), and another one developing mainly
		toward SE (Event #3). Starting also at 00:30 UT a ragged feature
		(brighter than the other features described above) develops
		toward WSW - SW (Event #4), which is followed at 03:06 by a
		twisted feature. Also at that time, an elongated ragged feature
		can be seen developing toward NE (Event #5).The five events are
		first seen in C3 by 01:42 UT: Event #1 just barely seen above 
		the SW Limb, Event #2 (on NW) and #3 (on SE) further out, Event
		#4 above the WSW Limb as a bright ragged feature, and Event #5
		just above the NE Limb.  
 		For reference, the mean plane-of-sky speed for the LE of the
		different events is shown below (based on C3 data):
		Event #1: PA 128 --> 412 km/sec (practically no acceleration)
		Event #2: PA 291 --> 484 km/sec (very diffuse LE)
		Event #3: PA 086 --> 599 km/sec (very diffuse LE)
		Event #4: PA 241 --> 388 km/sec (practically no acceleration)
		Event #5: too difficult to track it accurately, but its
		speed is in the 350-450 km/sec range.
		GOES did not record any significant X-ray activity by the time. 
		On the other hand, EIT Fe XII images show the lift-off of a 
		filament located around equatorial latitudes, past half way to
		the W Limb, starting at around 18:00 UT. This signature is 
		likely to be the EIT counterpart of either what we called Event
		#4 or the twisted feature coming behind. Other than that, there
		is no other visible signature on the disk that could be related
		to the other events mentioned above. By the time of writing is
		not clear whether Events #2 and #3 are related to any of the
		other two events or are monster of a diferent nature. As for
		Event #1, it has therefore been determined as a 'full' HALO CME,
		backsided. 

10:30 UT HALO   Very faint and diffuse circular front in the northern 
		hemisphere, brighter above the ENE Limb. By 10:54 UT the C2
		occultor is completely surrounded. By that time, a brighter 
		front begins to be visible above the E Limb up to the S Pole.
		Inspection of the C2 running difference movie shows an almost
		perfect	circular front inside the diffuse circular front
		described at the beginning. The C3 occultor is completely
		surrounded by this second feature at 11:42 UT. For reference, 
		the mean plane-of-sky speed for the LE of the various features 
		is given below (based on C3 data):
	      - LE of the diffuse circular front at PA 120: 692 km/sec 
		(practically no acceleration)
	      - LE of the second circular front at PA 115: 517 km/sec 
		(practically no acceleration)
		GOES did not record any significant X-ray activity by the 
		time. Likewise, EIT Fe XII images do not show any signature 
		that could be related to the Halo event. The event has therefore
		been determined as a 'full' halo CME, backsided. 

18:30 UT  WSW	Faint ragged loop front that fades throughout C3.

19:31 UT  WNW	Small and bright loop front followed by a diffuse front slightly
		to N moving apparently faster. They fade througout C3.

19:54 UT  ENE	Very faint and not well defined front. It fades throughout C3.
		Gusty outflow before and after.

2004/09/04 (Saturday)

02:06 UT  W  	Bright and elongated loop front. It fades throughout C3.

06:54 UT  E  	Bright loop front. By 07:31 UT a wide and bright loop front 
	(HALO)	can be seen developing mainly toward E accompanied by a much 
		fainter and diffuse loop front extending all above the N Pole. 
		By 08:06 UT the C2 occultor is completely covered (with very 
		faint extensions above the SW Limb). Please note that by 08:30
		UT, above the NE Limb, an apparently flat ragged front is
		discernible superposed in the LOS with our event. 
		On the other hand, features corresponding to the halo event are 
		first seen in C3 at 07:42 UT above the E - ESE Limb, exhibiting 
		a diffuse front ahead of a bright loop front. The C3 occultor is 
		covered by 08:42 UT. For reference, the mean plane-of-sky speed 
		for the LE of various features is given below (based on C3 data):
	      - LE of the diffuse front at PA 112:     970 km/sec 
	      - LE of the bright loop front at PA 112: 850 km/sec 
	      - LE of the outermost feature at PA 295: 457 km/sec
		GOES did not record any significant X-ray activity by the time. 
		EIT Fe XII images show a CME signature that develops above the 
		E Limb, starting at around 07:36 UT. Such an ejection seems to 
		be rooted with one leg on the visible side and the other one 
		behind the limb. It is most likely the EIT counterpart of the 
		'flat' front mentioned above. As for the halo event, there is 
		no visible signature on the Earthside of the Sun as seen on EIT
		Fe XII images that could be associated. The event has therefore 
		been determined as an asymmetric 'full' halo CME, backsided. 

09:54 UT  E 	Very ragged loop front. It fades throughout C3. Gusty outflow.
		Infalling material on SE along the rest of the day.

18:30 UT  W	Very faint spray-like front.

2004/09/05 (Sunday)

05:30 UT  E Limb	Faint ragged loop front that fades close to the inner
			edge of C3.

06:30 UT  N West	Big bright loop front. EIT Fe XII running difference
			images show CME signature from nearby N20W60 travelling
			toward NW starting at around 05:24 UT. Apparent dimming
			centered on source.

06:54 UT  S Pole	Very faint asymmetric loop front developing slowly.
			It fades throughout C3.

07:54 UT  E Limb	Wide and bright loop front with structured interior. 
			It is followed at 12:54 UT by a small and relatively
			bright front. By 07:25 UT EIT Fe XII running difference
			images show an apparently backsided CME above the E Limb.
			No significant X-ray activity reported by GOES.

18:54 UT  E Limb 	Another wide and bright loop front with structured 
			interior. Starting at 18:24 UT EIT Fe XII running
			difference images show an apparently backsided CME above
			the E Limb. No significant X-ray activity reported by
			GOES.

20:58 UT  E Limb	Another wide and bright loop front moving apparently 
			faster than the one at 18:54 UT. Difficult to give an
			exact time of first appearance due to the superposition
		 	of events in the LOS. By 23:42 UT the first front is
			apparently surpassed in the C3 FOV by this second front.
			Close inspection of the C2-C3 sequence of images seems 
			to reveal a third front (even more explosive) starting
			also at around 20:58 UT and developing slightly toward
			ESE. By 00:18 UT a faint halo seems to develop in C3. 
			Nothing sifnificant in Fe XII running difference images
			on the disk. Most likely, the source for the 3 events 
			was in the backside as for the event at 18:54 UT. 
			Likewise, no significant X-ray activity was reported by
			GOES by the time. Gusty outflow well into next day.

2004/09/06 (Monday)

05:54 UT  ES East 	Ragged loop front. It is preceded by several small 
			ragged front on E, and also afterward (intermitent 
			activity).

16:30 UT  S East	Slow development of a system of asymmetric loops 
			that spans later all above the S Pole. Continuous
			development of loops well into next day. As time goes 
			by, the main direction of the flow seems to rotate
			toward W, like following the Sun's rotation.

2004/09/07 (Tuesday)

15:30 UT  E Limb	Bright and wide loop front with structured interior and
			trailing material. By 16:54 UT an apparent different
			structure seems to develop inside the previos CME and
			spanning up to above the S Pole. EIT Fe XII running
			difference images show a big backsided above the E Limb
			starting at around 14:00 UT. Please note that between
			15:24 - 16:12 UT an intensity disturbance is seen
			travelling all above the SW Limb (maybe related to the
			second feature seen in C2 FOV?).