Solar Terrestrial Activity Report

Last major update issued on September 25, 2011 at 06:10 UTC. Minor update posted at 11:45 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 23, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2113 [July-August 2011] - 2114 [August-September 2011] NEW
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet on September 24. Solar wind speed ranged between 313 and 357 km/s.

Solar flux measured at 23h UTC on 2.8 GHz was 168.7 (increasing 67.7 over the last solar rotation, and the highest non-flare enhanced solar flux measurement of cycle 24. The measurements at 17 and 20h UTC were both flare enhanced). The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.6). Three hour interval K indices: 00012122 (planetary), 10112122 (Boulder).

The background x-ray flux is at the class C3 level.

At midnight UTC the visible solar disk had 8 spotted regions (in 2K resolution SDO images).

Region 11295 [N24W84] developed further in the trailing penumbra which became very complex with a strong magnetic delta structure. A major flare is possible as the region rotates over the northwest limb. Flares: C5.9 at 07:04, C2.2 at 08:43, M1.7 at 16:58 (not reported by SWPC), M2.7 at 18:19 (not reported by SWPC as they failed to separate this event from another event which started earlier in region 11302) UTC.
Region 11301 [N20E02] lost all penumbra on the leader spots. The region has many tiny, widely scattered spots with polarity intermixing again occuring in the northwestern part.
Region 11302 [N13E50] has a small magnetic delta structure in the northeastern part of the leading penumbra. A much more significant delta exists in the central penumbra where a realtively large positive polarity umbra is sandwiched between two fairly large negative polarity umbrae. As long as this delta exists the region will continue to produce M and X flares. Flares: major impulsive X1.9/2B at 09:40 (associated with a small CME), C2.7 at 11:31, major M7.1/1B long duration event peaking at 13:20 (associated with a huge, fast, wide CME), M3.1 at 17:25 (wrongly attributed to region 11295 by SWPC), M2.8 at 18:05, M3.0 at 19:21, major M5.8 at 20:36 UTC. Early on September 25 the region has produced an M4.4 flare at 02:33 (with some contribution from region 11303 which flared simultaneously), and a major M7.4 long duration event peaking at 04:50 UTC. The latter event is likely to have been associated with a large CME.
New region 11303 [S28W66] emerged in the southwest quadrant on September 23 and was numbered the next day by SWPC. The region developed rapidly during the latter half of the day with a magnetic delta structure forming in the very elongated penumbra. Further M class flaring is likely. Flares: M1.3 at 21:25 (not reported by SWPC) and M1.0 at 23:54 UTC.
New region 11304 [N12E22] emerged slowly and was quiet.

Spotted regions not numbered by NOAA/SWPC:
[S1223] reemerged on September 24 with a single tiny spot. Location at midnight: S15W33
[S1233] emerged in the northeast quadrant to the east of region 11301 on September 24. Location at midnight: N19E15

Minor update added at 11:45 UTC on September 25: A fairly weak solar wind shock was observed at ACE near 11h UTC, the arrival of the CME associated with the X1 event in region 11302 on September 22. Region 11303 generated an M1.3 flare at 07:05 and an M1.5 event at 09:35 UTC. Region 11302 was the source of an M3.1/1N event at 08:49 UTC.

Coronal mass ejections (CMEs)

September 22: An unusually large and wide CME was observed after the X1.4 event in region 11302. While it is rare that limb events cause geomagnetic storming, this CME could when it arrives, probably on September 25.
September 23: No obviously Earth directed CMEs observed.
September 24: A huge, fast and wide (asymmetrical) full halo CME was observed in LASCO following an M7.1 LDE in region 11302. This CME will likely reach Earth on September 26 and cause active to major storm conditions.

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 coronal hole (CH477) in the southern hemisphere will likely rotate into an Earth facing position on September 28.

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 fair. Propagation on long distance northeast-southwest paths is poor to fair.


The geomagnetic field is expected to be initially quiet on September 25. A CME associated with the X1.4 flare on September 22 could arrive during the day and cause unsettled to minor storm conditions. Another CME impact is likely on September 26 and could result in active to major storm conditions that day and on September 27. If the current situation in region 11302 persists we can expect lots of geomagnetic storm intervals until at least October 5.

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
11295 2011.09.11
7 15 N26W84 0500 EKC DKC beta-gamma-delta
11296 2011.09.12
    N26W70         plage
11301 2011.09.17
16 31 N18W01 0090 FSO CSI

area: 0070

location: N20E02

S1222 2011.09.20     N22W29           plage
S1223 2011.09.20   1 S15W23 0000   AXX    
S1224 2011.09.20     N10W28           plage
S1225 2011.09.21     S15E03           plage
11302 2011.09.21
12 37 N12E47 1300 FKC FHC beta-gamma-delta

location: N13E50

S1227 2011.09.21     N12W59           plage
S1228 2011.09.21     S17W31           plage
S1229 2011.09.21     S08W44           plage
11303 2011.09.23
1 14 S28W66 0030 CSI DAI beta-gamma-delta

area: 0100

11304 2011.09.24 2 6 N12E22 0010 BXO BXO    
S1231 2011.09.24   1 N13E84 0150   HSX    
S1233 2011.09.24   1 N19E15 0000   AXX    
Total spot count: 38 106  
Sunspot number: 88 186  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 68 141  (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): 53 61  k * (sunspot number). k = 0.6 for SWPC. k = 0.33 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
2011.09 131.2 (1) 86.5 (2A) /  108.1 (2B) (56.7 predicted, +2.3) (10.16)

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.