Solar Terrestrial Activity Report

Last major update issued on September 8, 2013 at 02:55 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 23-24 (last update September 1, 2013)] [Cycle 24 progress (last update September 1, 2013) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 1, 2013)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 1, 2013)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 5, 2013)]

[POES auroral activity level since October 2009 - updated January 26, 2013]
[Solar polar fields vs solar cycles - updated September 5, 2013]
[Presentation 3rd SSN Workshop, Tucson, 2013 (pdf)]

Recent activity

The geomagnetic field was very quiet on September 7. Solar wind speed at SOHO ranged between 315 and 376 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 98.5 (decreasing 11.9 over the last solar rotation). The Potsdam WDC planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.8). Three hour interval K indices: 01110010 (planetary), 11112211 (Boulder).

The background x-ray flux was at the class B2 level.

At midnight UTC the visible solar disk had 5 spotted active regions (in 2K resolution SDO images).

Region 11836 [N10W76] decayed slowly and quietly.
Region 11838 [S04E43] gained a few spots, however, the only penumbra containing umbrae decayed.

Spotted regions not numbered by SWPC:
S2658 [S13E50] gained trailing spots and was quiet.
S2661 [S20E21] decayed slowly and quietly.
New region S2663 [N31W44] emerged with penumbra spots.

Coronal mass ejections (CMEs)

September 5-7: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.

Coronal holes

Coronal hole history (since October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH584) in the northern hemisphere was in an Earth facing position on September 7.  CH584 is the western part of what used to be a large coronal hole and has slowly decreased in size after rotating into view. The eastern part of that large coronal hole, now CH585, will likely rotate into an Earth facing position on September 9-11.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet on September 8-9. On September 10-11 there's a chance of quiet to unsettled conditions due to effects from CH584. Effects from CH585 could cause quiet to minor storm conditions on September 12-14.

1) Effects from a coronal hole could reach Earth within the next 5 days. When the high speed stream has arrived the color changes to green.
2) Effects from a CME are likely to be observed at Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.

Active solar regions

(Click on image for 2K resolution) Compare to the previous day's image. 0.5k image

When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue is positive.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC. Comments are my own, as is the STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers.

Active region	Date numbered detected	Spot count			Location at midnight	Area	Classification		SDO / HMI 4K continuum image with magnetic polarity overlay		Comment
		SWPC	STAR SDO				SWPC	STAR	Current	Previous
			2K	1K
11836	2013.08.26 2013.08.27	2	1	1	N10W78	0090	CAO	HAX
S2646	2013.08.30				S13W40						plage
S2648	2013.08.30				N42W44						plage
11837	2013.08.31 2013.09.02	2			S17W88	0050	HAX				rotated out of view
S2651	2013.09.01				N20W36						plage
S2655	2013.09.03				N03W00						plage
S2656	2013.09.03				S07W42						plage
11838	2013.09.04 2013.09.05	1	9	3	S05E41	0030	HAX	CRO			location: N04E43
S2658	2013.09.05		4		S13E50	0011		BXO
S2659	2013.09.05				N15W41						plage
S2660	2013.09.05				N13W06						plage
S2661	2013.09.05		2	1	S20E21	0007		BXO
S2662	2013.09.06				N07W15						plage
S2663	2013.09.07		2	1	N31W44	0005		AXX
Total spot count:		5	18	6
Sunspot number:		35	68	46	(total spot count + 10 * number of spotted regions)
Weighted SN:		20	26	14	(Sum of total spot count + classification weighting for each AR. Classification weighting: X=0, R=3, A/S=5, H/K=10)
Relative sunspot number (Wolf number):		21	24	25	k * (sunspot number). k = 0.6 for SWPC, k = 0.35 for STAR SDO 2K, k = 0.55 for STAR SDO 1K

Monthly solar cycle data

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2A) Current impact on the monthly sunspot number based on the Boulder (NOAA/SWPC) sunspot number (accumulated daily sunspots / month days). The official SIDC international sunspot number is typically 30-50% lower. 2B) Boulder SN current month average to date. 2C) STAR SDO 1K Wolf number 30 day average.
3) Running average based on the quicklook and definitive Potsdam WDC ap indices. Values in red are based on the definitive international Potsdam WDC ap indices.

This report has been prepared by Jan Alvestad. It is based on the analysis of data from whatever sources are available at the time the report is prepared. All time references are to the UTC day. Comments and suggestions are always welcome.

SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.