Solar Terrestrial Activity Report

Last major update issued on September 18, 2011 at 06:35 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 15, 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 to major storm on September 17. Solar wind speed ranged between 346 and 535 km/s. A solar wind shock was observed at SOHO at 03:05, the arrival of the CME observed on Sept.13/14. After the shock the interplanetary magnetic field was at times moderate to strongly southwards causing major geomagnetic storming. The peak of the storm was during the 14-17h UTC interval when the 3-hour ap index reached 111.

Solar flux measured at 20h UTC on 2.8 GHz was 144.8 (increasing 43.9 over the last solar rotation). The planetary A index was 32 (STAR Ap - based on the mean of three hour interval ap indices: 32.4). Three hour interval K indices: 03346643 (planetary), 13444532 (Boulder).

The background x-ray flux is at the class B9 level.

At midnight UTC the visible solar disk had 12 spotted regions (in 2K resolution SDO images).

Region 11289 [N23W65] was mostly unchanged and quiet.
Region 11290 [S11W81] decayed slowly and was mostly quiet.
Region 11292 [N09W15] decayed slowly and quietly.
Region 11294 [S18W38] decayed slowly and could become spotless today.
Region 11295 [N22E05] was mostly quiet but has the potential to produce C and M class flares.
Region 11296 [N27E22] decayed slowly and quietly.
Region 11298 [N15E09] decayed slowly and quietly.
Region 11299 [S19E12] developed slowly and quietly.

Spotted regions not numbered by NOAA/SWPC:
[S1214] reemerged with a single spot on September 16. Location at midnight: S25W46
[S1218] emerged in the northwest quadrant on September 16 and developed significantly on September 17. The region could produce C flares. Location at midnight: N24W32
[S1219] rotated partly into view at the northeast limb late on September 17. C flares are possible, maybe even M flares. Location at midnight: N24E88
[S1220] emerged in the northwest quadrant on September 17. Location at midnight: N17W17

Coronal mass ejections (CMEs)

September 15-17: No obviously Earth directed CMEs observed.

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

No obvious coronal holes are currently in or near potentially geoeffective positions.

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

Forecast

The geomagnetic field is expected to be quiet on September 18-20 with a chance of unsettled intervals on Sept.18.

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
11289 2011.09.05
2011.09.06
5 10 N22W67 0380 HHX CHO

location: N23W65

11290 2011.09.07
2011.09.09
4 6 S13W84 0010 BXO CRO

location: S11W81

area: 0020

11291 2011.09.09
2011.09.10
2   N21W93 0010 BXO     rotated out of view
11294 2011.09.10
2011.09.12
1 2 S16W45 0010 HRX AXX area: 0000

location: S18W38

S1203 2011.09.10     N07W28           plage
11292 2011.09.11 1 2 N10W17 0020 HRX BXO location: N09W15

area: 0000

11295 2011.09.11
2011.09.12
17 32 N22E04 0210 DAI DAI  
11293 2011.09.11
2011.09.12
    N17W79         plage
11296 2011.09.12
2011.09.13
9 20 N25E19 0130 CAO CAO

location: N27E22

S1212 2011.09.12     N38W47           plage
S1213 2011.09.13     S18W53           plage
S1214 2011.09.13   1 S25W46 0000   AXX  
11299 2011.09.14
2011.09.16
6 26 S20W02 0040 DSO DRI location: S20W00
11298 2011.09.14 3 18 N15E09 0100 DSO CRO beta-gamma

area: 0020

S1218 2011.09.16   13 N24W32 0060   CAO  
S1219 2011.09.17   2 N24E88 0080   HSX    
S1220 2011.09.17   2 N17W17 0000   AXX    
Total spot count: 48 134  
Sunspot number: 138 254  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 84 173  (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): 83 84  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
2011.09 123.0 (1) 61.7 (2A) /  108.8 (2B) (56.7 predicted, +2.3) (12.62)

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.