Solar Terrestrial Activity Report

Last major update issued on September 7, 2011 at 04:50 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 5, 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 on September 6. Solar wind speed ranged between 351 and 431 km/s, weakly under the influence of a low speed stream from CH474.

Solar flux measured at 20h UTC on 2.8 GHz was 111.5 (increasing 21.2 over the last solar rotation). The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 6.6). Three hour interval K indices: 12222112 (planetary), 23222222 (Boulder).

The background x-ray flux is at the class B6 level.

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

Region 11281 was quiet with a few small spots emerging in the northern part of the region.
Region 11283 became more complex as the major penumbrae merged into one penumbra. There's a strong magnetic delta structure in the northern part of this penumbra. Further major flares are possible. Flares: major M5.3/1B at 01:50 (associated with a strong type II radio sweep and a halo CME. Most of the ejected material was observed over the northern limbs and there's a chance the core of the CME will not reach Earth), major impulsive X2.1 flare at 22:20 UTC. The latter event was associated with a slow and wide CME with Earth apparently in the path of the core CME.
Region 11287 was quiet and stable.
Region 11288 was quiet and stable.
New region 11289 rotated into view at the northeast limb.

Spotted regions not numbered by NOAA/SWPC:
[S1193] reemerged with a single tiny spot on September 6. Location at midnight: N24W28
[S1196] emerged in the southeast quadrant on September 4. Location at midnight: S21E07

Coronal mass ejections (CMEs)

September 4-5: No obviously Earth directed CMEs were observed in LASCO or STEREO imagery.
September 6: The CME associated with the major M5 flare in region 11283 was mainly directed outside a direct Earth path. A minor disturbance is possible starting late on September 8 or during the first half of September 9. A wider CME was observed following the X2 flare. This CME will likely impact Earth, probably arriving during the latter half of September 9.

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) will likely rotate into an Earth facing position on September 8-9.

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 quiet to unsettled on September 7-8. September 9 could see the arrival of 2 CMEs, the latter has the potential to cause active to major storm conditions. Disturbed conditions are likely to continue on September 10. On September 11-12 a high speed stream from CH475 could cause quiet to active conditions.

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
11277 2011.08.24
2011.08.25
1 1 N18W93 0060 HSX     rotated out of view
11279 2011.08.25     N13W87            
11281 2011.08.27
2011.08.28
2 9 S18W51 0010 BXO BXO

location: S17W48

11283 2011.08.29
2011.08.30
23 37 N14W18 0200 EAI DHC

beta-gamma-delta

area: 0400

S1190 2011.08.30     S13W30           plage
11287 2011.09.02
2011.09.03
5 8 S31E25 0100 CSO CSO  
S1193 2011.09.02   1 N24W28 0000   AXX    
S1194 2011.09.02     N22W49           plage
11288 2011.09.03 1 3 N19E20 0000 AXX BXO  
S1196 2011.09.04   3 S21E07 0000   AXX  
11289 2011.09.05
2011.09.06
1 5 N24E78 0190 HSX CHO  
Total spot count: 33 67  
Sunspot number: 93 137  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 53 92  (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): 56 62  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
(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
2011.09 115.8 (1) 22.3 (2A) /  111.7 (2B) (56.7 predicted, +2.3) (6.46)

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.