Solar Terrestrial Activity Report

Last major update issued on September 23, 2011 at 04:35 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 21, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2112 [July 2011] -  2113 [July-August 2011]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet on September 22. Solar wind speed ranged between 344 and 412 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 150.8 (increasing 46.2 over the last solar rotation). The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.3). Three hour interval K indices: 10001012 (planetary), 11012222 (Boulder).

The background x-ray flux is at the class C1 level.

At midnight UTC the visible solar disk had 7 spotted regions (in 2K resolution SDO images).

Region 11295 [N23W62] is likely to produce further M class flares as there's still a magnetic delta structure in the eastern part of the region. Flares: C6.6 at 04:28, M1.1 at 10:00 (wrongly attributed to region 11302 by SWPC), C4.0 at 20:20, C5.5 at 22:30, C4.1 at 23:56 UTC. The region was the source of and M1.6/1N long duration event peaking at 02:00 UTC on September 23.
Region 11296 [N25W43] was quiet and stable.
Region 11299 [S20W68] decayed slowly and quietly.
Region 11301 [N20E27] was quiet. There's slight polarity intermixing to the north of the leading penumbra.
New region 11302 [N13E76] rotated partly into view at the northeast limb on September 21 and was numbered the next day by SWPC. Further X class flares are possible as this is a magnetically complex region, particularly in the trailing spot section. Flare: X1.4/2N long duration event peaking at 11:01 UTC. The shock wave from this event was global (observed in the corona all around the visible disk). The CME was very wide and was observed as full halo in STEREO A and B and LASCO (asymmetrical). Due to its origin near the northeast limb it is difficult to estimate the CME arrival time at Earth. Proton flux levels have been increasing slowly since the event and a proton event could start later today (possibly with contribution from events in region 11295 as well)

Spotted regions not numbered by NOAA/SWPC:
[S1223] emerged in the southeast quadrant on September 20. Location at midnight: S16E06
[S1227] emerged in the northwest quadrant on September 21. Location at midnight: N12W33

Coronal mass ejections (CMEs)

September 20-21: No obviously Earth directed CMEs observed.
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.

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

An extension of the southern polar coronal hole rotated across the central meridian on September 21 and is likely too far to the south to cause geomagnetic effects. Another coronal hole in the northern hemisphere will likely rotate into an Earth facing position on September 23 and is probably too far to the north to become geoeffective.

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.

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

Forecast

The geomagnetic field is expected to be mostly quiet on September 23-24. A CME arrival is possible on September 25 and could cause unsettled to minor storming.

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
detected
Spot count Location at midnight Area Classification SDO / HMI 4K continuum
image with polarity overlay
Comment
SWPC STAR SDO SWPC STAR Current Previous
11295 2011.09.11
2011.09.12
19 33 N22W62 0350 EKC EAC beta-gamma-delta
11296 2011.09.12
2011.09.13
1 1 N26W44 0010 AXX AXX  
11299 2011.09.14
2011.09.16
2 3 S19W64 0010 BXO BXO location: S20W68
11298 2011.09.14     N16W61          
11301 2011.09.17
2011.09.18
12 33 N19E29 0120 ESO DSO beta-gamma

area: 0080

S1222 2011.09.20     N22W03         plage
S1223 2011.09.20   4 S16E06 0010   BXO  
S1224 2011.09.20     N10W02           plage
S1225 2011.09.21     S15E29         plage
11302 2011.09.21
2011.09.22
2 30 N11E74 0480 EKI EHC beta-gamma-delta

location: N13E76

area: 0950

S1227 2011.09.21   1 N12W33 0000   AXX  
S1228 2011.09.21     S17W05         plage
S1229 2011.09.21     S08W18         plage
Total spot count: 36 105  
Sunspot number: 86 175  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 61 125  (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): 51 58  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
(3)
2008.07 65.7 (SF minimum) 0.5 2.8 (-0.4)  
2008.12 69.2 0.8 1.7 (-)
sunspot minimum
3.25
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
2011.09 128.3 (1) 80.6 (2A) /  109.9 (2B) (56.7 predicted, +2.3) (10.78)

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.