Solar Terrestrial Activity Report

Last major update issued on September 10, 2011 at 05:00 UTC. Minor update posted at 10:55 UTC

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update September 1, 2011)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 1, 2011)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 1, 2011)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 1, 2011)]

[POES auroral activity level since October 2009 - updated September 8, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2112 [July 2011] -  2113 [July-August 2011] NEW
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to severe storm on September 9. Solar wind speed ranged between 284 and 499 km/s. The CME observed after the X2 flare on September 6 arrived at ACE at 11:50 UTC with the interplanetary magnetic field becoming strongly southwards at times for the remainder of the day. Several magnetometers recorded K9 conditions at the peak of the disturbance.

Solar flux measured at 20h UTC on 2.8 GHz was 111.8 (increasing 28.7 over the last solar rotation). The planetary A index was 36 (STAR Ap - based on the mean of three hour interval ap indices: 35.5). Three hour interval K indices: 11005755 (planetary), 12015644 (Boulder).

The background x-ray flux is at the class B4 level.

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

Region 11283 decayed slowly losing spots and penumbral area. While the magnetic delta structure has disintegrated, there's still polarity intermixing in the central part of the region. C flares are likely and there's a chance of an M class flare. Flares: C1.2 at 02:03, M2.7/1N at 06:11, M1.2/1F at 12:49, C3.2 at 14:59, C1.1 at 23:09 UTC
Region 11287 added a few spots and was quiet.
Region 11289 added several spots in a new penumbra to the south of the large penumbra. The new penumbra could easily develop a magnetic delta structure. C and minor M class flares are possible.
New region 11290 emerged in the southeast quadrant on September 7 and was noticed by SWPC two days later.

Spotted regions not numbered by NOAA/SWPC:
[S1200] emerged in the northeast quadrant on September 9. Location at midnight: N23E13

A large filament eruption was observed beginning at 00:59 UTC on September 10 in the central northern hemisphere. At 03:24 UTC STEREO-A observed a CME, mainly over the northern hemisphere. It's too early to tell if this CME will impact Earth.

A very active region is approaching the northeast limb and should rotate into view within a couple of days.

Minor update added at 10:55 UTC on September 10: The CME earlier today was at least partial halo. While the core of the CME will not reach Earth, there's a chance of a flank impact on September 13. Region 11283 produced an M1.1 flare 07:40 UTC today.

Coronal mass ejections (CMEs)

September 7: Lots of CMEs were observed during the day, most were backsided. The CME associated with the X1.8 event in region 11283 may cause a flank impact at Earth on September 10 resulting in a brief increase in disturbance levels.
September 8: Another day with several CMEs observed. None appears to be Earthbound as most of the activity was backsided.
September 9: No obviously Earth directed CMEs were observed. There was a CME after the M2 event in region 11283 but its path makes any terrestrial effects unlikely. Several backsided CMEs were noted.

Coronal holes

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

A recurrent trans equatorial coronal hole (CH475) was in an Earth facing position on September 8-10. Another and smaller trans equatorial coronal hole (CH476) will rotate into an Earth facing position on September 11.

The above coronal hole map is based on a new method where coronal holes are detected automatically. The method may need some fine tuning, however, 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 the new method, the extent and intensity of both holes are consistent with other data sources.


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


The geomagnetic field is expected to be unsettled to minor storm on September 10 with a chance of an isolated major storm interval due to CME effects. Quiet to active is likely on September 11-15 due to coronal hole effects.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)

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

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
Spot count Location at midnight Area Classification SDO / HMI 4K continuum
image with polarity overlay
11281 2011.08.27


11283 2011.08.29
12 14 N17W55 0210 EAO DSO


location: N14W60

11287 2011.09.02
2 7 S29W16 0060 HSX CSO location: S30W15
11288 2011.09.03
    N19W22           plage
S1196 2011.09.04     S19W31           plage
11289 2011.09.05
6 12 N22E37 0380 DHO CHO beta-gamma

location: N23E39

11290 2011.09.07
5 10 S15E29 0030 CRO DRO formerly region S1199

almost DAO classification

location: S15E31

S1200 2011.09.09   2 N23E13 0010   BXO    
Total spot count: 25 45  
Sunspot number: 65 95  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 48 65  (Sum of total spot count + classification adjustment for each AR. Classification adjustment: X=0, R=3, A/S=5, H/K=10)
Relative sunspot number (Wolf number): 39 43  k * (sunspot number). k = 0.6 for SWPC. k = 0.45 for STAR SDO

Monthly solar cycle data

Month Average measured solar flux International sunspot number (SIDC) Smoothed sunspot number Average ap
2008.07 65.7 (SF minimum) 0.5 2.8 (-0.4)  
2008.12 69.2 0.8 1.7 (-)
sunspot minimum
2010.06 72.5 13.6 16.4 (+0.9) 8.17 / 6.85
2010.07 79.8 16.1 16.7 (+0.3) 6.31 / 5.15
2010.08 79.2 19.6 17.4 (+0.7) 8.49 / 7.77
2010.09 81.1 25.2 19.6 (+2.2) 5.33 / 5.45
2010.10 81.6 23.5 23.2 (+3.6) 6.07 / 6.27
2010.11 82.5 21.5 26.5 (+3.3) 4.80 / 5.50
2010.12 84.2 14.4 28.8 (+2.3) 3.41 / 4.35
2011.01 83.6 19.1 31.0 (+2.2) 4.32 / 5.51
2011.02 94.6 29.4 33.4 (+2.4) 5.41 / 6.44
2011.03 115.0 56.2 (36.2 predicted, +2.8) 7.79 / 8.18
2011.04 112.6 54.4 (39.1 predicted, +2.9) 9.71 / 8.83
2011.05 95.8 41.6 (42.4 predicted, +3.3) 9.18 / 8.94
2011.06 95.8 37.0 (46.1 predicted, +3.7) 8.96
2011.07 94.2 43.9 (50.3 predicted, +4.2) 9.14
2011.08 101.7 50.6 (54.4 predicted, +4.1) 8.16
2011.09 114.4 (1) 28.1 (2A) /  93.6 (2B) (56.7 predicted, +2.3) (9.33)

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 preliminary daily SWPC ap indices. Values in red are based on the official NGDC 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.