LASCO Activity Report for
September 1, 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

KEYHOLE OPERATIONS:
-------------------
SOHO keyhole #10 telemetry period: Aug 31-Sep 28, 2005.

EIT will go to CCD bakeout between Sep 2 23:00 UT - Sept 23 10:00 UT 
with its mini-cal pre and post sets as folows:
2005/09/02 19:00:00 - 2005/09/03 01:00:00
2005/09/23 20:00:00 - 2005/09/24 00:20:00

During the Telemetry Keyhole LASCO will be in improved synoptic cadence 
of C2 at 12 mins cadence and C3 at 30 mins cadence, including daily 
orange/blue filter fielding images.

The SOHO roll back to 0 deg is scheduled for Thursday Sept 8, 2005.
LASCO will safe for the S/C roll (also Station Keeping and Momentum 
Management) on Wed Sept 7 at 11:00 UT and re-open Saturday Sept 10 
at 12:00 UT.

2005/08/31 (Wednesday)

07:31 UT  N East	Very faint expanding loop front mainly developing toward
			NE, first seen as a very faint and diffuse front. By
			09:06 UT, the angular span of the front in C2 seems to
			cover from the ESE Limb up up NW Limb (clockwise), 
			though in NW is too faint to define its edge. It is 
			first seen in C3 above the NE Limb at 08:42 UT. The 
			main plane-of-sky speed of the event at PA 35 was ~ 
			385 km/sec (last frame used: 10:42 UT; LE at ~ 9 
			solar radii). GOES reported no significant activity by
			the time prior to the LASCO event. On the other hand,
			EIT 195 images show a small ejection starting at 06:12
			UT, on the southern hemisphere close to the central
			meridian (far west of AR 10806), just on the border 
			of the southern coronal hole, developing toward SE (see
			next entry).

07:31 UT  S East	Diffuse and rather elongated front.

10:06 UT  N East	Another diffuse front (a little brighter than the one
			at 07:31 UT on NE). By 11:30 UT, the event seems to 
			span in C2 from ESE well up to the NW limb (clockwise).
			It is first clearly seen in C3 above the NE Limb at 
			10:42 UT. This event seem to coalesce with the one
			at 07:31 UT on NE in the C3 FOV  by 12:18 UT (at about 
			11 solar radii), either because the second event is
			faster or the first one becomes too faint to be
			distinguished. The mean plane-of sky speed of the event
			at PA 40 was ~ 445 km/sec (last frame used: 13:42 UT; 
			LE at ~ 12.5 solar radii). GOES reported no significant
			activity by the time prior to the LASCO event, except 
			for a B3.2 X-ray flare on NOAA AR 10806 (S17E32) between
			09:52 - 10:08 UT with peak emission at 10:02 UT. EIT 195
			images show a dimming region just on SE of AR 10806
			starting at 10:00 UT, i.e., during the time of the B3.2
			X-ray flare. Based on the global appearance on C3 of the
			events reported to start at 07:30 UT and the present 
			one, the complex event could be classified as a faint 
			and complex Partial (at least) Halo Event. Though the
			timing of the EIT events reported seem to correlate
			with the respective LASCO events, the corresponding
			spatial location on the disk doesn't. Therefore, it is
			hard to be sure about the location of their source.

11:30 UT  W Limb	Small brightening just appearing above the W Limb
			develops as a bright loop front. It is followed
			(apparently about one hour later) by a fainter and
			diffuse expanding loop front with faint extensions on 
			E. The C2 occulting disk appears fully covered by 
			13:31 UT. The "halo" looks rather flat over the poles, 
			and elongated toward W and E. The event is first seen 
			in C3 above the W Limb at 12:42 UT. The C3 occulting 
			disk seems to be fully surrounded by 12:42 UT. The 
			event fades throughout C3. The mean plane-of-sky speed 
			of the outermost edge of the event on W (PA 285) was 
			~ 860 km/sec. GOES reported a long duration C2.0 X-ray
			flare on NOAA AR 10803 (N13W13) between 10:26 - 12:51 UT
			with peak emission at 11:51 UT. EIT 195 images show a
			brightening on AR 10803 starting at 10:36 UT all along
			the magnetic inversion line (extending E-W) followed by 
			a dimming region mainly to W and NW of the AR. Post 
			flare loops. In summary, the event has therefore been
			determined as a faint Full Halo Event, frontsided,
			associated to a C-class X-ray event on NOAA AR 10803.

17:54 UT  WN West	Couple of small ragged fronts.

22:30 UT  HALO		The event appears as a very bright and thick loop front
			extending all the way from the E limb to the W limb
			passing over the S Pole with diffuse (though rather
			bright) extensions ahead (mainly toward S). The thick
			loop front seems to close the circle around the occulter
			(all the the way above the N Pole), though not as 
			bright. By 23:06 UT, the event appears brightest on SE. 
			A new expanding loop front follows at 00:54 UT on next
			day on SE. Another one at 03:06 UT on SSE. The event 
			is first seen in C3 at 23:18 UT, already fully
			surrounding the occulting disk, the LE of the outermost
		 	part of the event on S (diffuse front ahead of the 
			thick loop-like structure) being at 13 solar radii. 
			The mean plane-of sky speed of the LE of several 
			features at various PA is given below:
			- PA 180: 1870 km/sec (LE of the diffuse front ahead of
			the loop-like structure, i.e., that of the shock)
			- PA 180: 1270 km/sec (LE of the loop-like structure)
			- PA 270: 1225 km/sec (LE of the loop-like structure)
			- PA 356:  745 km/sec (LE of the loop-like structure)
			- PA 050:  685 km/sec (LE of the loop-like structure)
			showing practically no acceleration in all cases.
			GOES reported no significant X-ray activity by the time
			of the event. Likewise, EIT 195 running difference 
			images do not show significant activity on the disk by
			the time prior to the LASCO event. However, they do show
			signatures of a huge backsided CME all above the S limb
 			starting at 22:24 UT. By 22:36 UT, the CME signature
			 can be seen almost above all around the limb. In
			summary, the event has therefore been determined as a
			symmetric and very strong Full Halo Event, backsided.

2005/09/01 (Thursday)

Time of the last C2 image under analysis: 12:06 UT.