Solar Terrestrial Activity Report

Last major update issued on September 16, 2012 at 05:40 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-24 (last update September 8, 2012)] [Cycle 24 progress (last update September 2, 2012) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 8, 2012)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 8, 2012)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 3, 2012)]

[POES auroral activity level since October 2009 - updated September 8, 2012]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to unsettled on September 15. Solar wind speed at SOHO ranged between 362 and 438 km/s under the influence of a low speed coronal hole stream.

Solar flux measured at 20h UTC on 2.8 GHz was 97.5 (increasing 1.3 over the last solar rotation). The Potsdam WDC planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 7.9). Three hour interval K indices: 33221113 (planetary), 22222212 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight UTC the visible solar disk had 6 spotted active regions (in 2K resolution SDO images).

Region 11566 [N23W76] decayed slowly and quietly.
Region 11569 [S12W01] decayed slowly and quietly.
Region 11571 [S13E19] was quiet and stable.
New region 11572 [N16W67] emerged on September 14 and was numbered the next day by SWPC.

Spotted regions not numbered by NOAA/SWPC:
S1912 [N14E37] was quiet and stable.
New region S1921 [N17E76] rotated into view early in the day.

Coronal mass ejections (CMEs)

September 13-15: 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 coronal hole (CH535) in the southern hemisphere was Earth facing position on September 13. A trans equatorial coronal hole (CH536) will likely rotate into an Earth facing position on September 17-18.

The above coronal hole map is based on a method where coronal holes are detected automatically. While the method may need some fine tuning, it has significant advantages over detecting coronal holes manually. The main improvement is the ability to detect coronal holes at and just beyond the solar limbs. Early results using this method for SDO images over a span of several weeks indicate a good match between coronal holes observed over the visible disk and their extent and position at the east and west limbs. Note that the polar coronal holes are easily detected using this method, the extent and intensity of both CHs are consistent with other data sources.

Propagation

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

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 16-17 due to weak coronal hole effects. A small CME associated with a filament eruption in the northwest quadrant on September 13 was not observed as a halo CME in LASCO imagery and has only a small chance of causing any geomagnetic effects. Quiet conditions are likely on September 18-20. A high speed stream from CH536 could cause quiet to active conditions on September 21-22.

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 higher resolution image) 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 (blue-green) 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
11566	2012.09.03	1	2	1	N23W76	0010	HRX	AXX
11567	2012.09.07				N16W58						plage
11569	2012.09.09 2012.09.10	8	11	5	S12W00	0180	ESO	ESO			area: 0280
11571	2012.09.10 2012.09.12	3	18	7	S13E19	0100	CSO	CSO			area: 0170
S1908	2012.09.10				S12W59						plage
11570	2012.09.11 2012.09.12				S13W76						plage
S1911	2012.09.11				S16W26						plage
S1912	2012.09.12		1		N14E37	0000		AXX
S1913	2012.09.12				N13E05						plage
S1914	2012.09.13				N20E44						plage
S1915	2012.09.13				N23E24						plage
S1916	2012.09.13				S20W25						plage
S1917	2012.09.14				S25W17						plage
11572	2012.09.14 2012.09.15	1	4	2	N15W70	0010	AXX	BXO			location: N16W67
S1919	2012.09.14				N31W29						plage
S1920	2012.09.14				S04W12						plage
S1921	2012.09.15		2	1	N17E76	0010		AXX
Total spot count:		13	38	16
Sunspot number:		53	98	66	(total spot count + 10 * number of spotted regions)
Weighted SN:		26	48	26	(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):		32	34	36	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) Month average to date.
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 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.