Solar Terrestrial Activity Report

Activity chart

Last major update issued on September 21, 2012 at 04:50 UTC.

[Solar and geomagnetic data - last month (updated daily)]
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[Solar cycles 21-24 (last update September 8, 2012)] [Cycle 24 progress (last update September 2, 2012) ]
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[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 8, 2012)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 8, 2012)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 3, 2012)]

[POES auroral activity level since October 2009 - updated September 8, 2012]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to unsettled on September 20. Solar wind speed at SOHO ranged between 379 and 585 km/s under the influence of a high speed stream from CH536. IMF Bz was near neutral most of the day resulting in only a weak disturbance.

Solar flux measured at 20h UTC on 2.8 GHz was 117.4 (increasing 13.2 over the last solar rotation). The Potsdam WDC planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 11.0). Three hour interval K indices: 33332222 (planetary), 32322322 (Boulder).

The background x-ray flux is at the class B2-B3 level.

At midnight UTC the visible solar disk had 9 spotted active regions (in 2K resolution SDO images).

Region 11569 [S12W70] decayed slowly and quietly.
Region 11571 [S14W45] decayed in the leading spot section while spots emerged in the trailing part.
Region 11573 [N18E14] was quiet and stable.
Region 11574 [S23W68] developed slowly and was mostly quiet.
Region 11575 [N07E50] was quiet and stable.
Region 11576 [S21E57] was quiet and stable.

Spotted regions not numbered by NOAA/SWPC:
S1924 [S22E14] decayed slowly and quietly.
S1927 [N20E68] developed slowly and quietly.
New region S1928 [N02E14] emerged in the easternmost part of a large filament. This development could cause the filament to become unstable and erupt.

The most interesting activity of the day was backsided. A large flare in a southern hemisphere region caused a full halo CME. See this image:

Coronal mass ejections (CMEs)

September 18-20: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.

Coronal holes

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

A trans equatorial coronal hole (CH536) was in an Earth facing position on September 17-19.

Coronal hole map

The above coronal hole map is based on a method where coronal holes are detected automatically. While the method may need some fine tuning, 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 this method, the extent and intensity of both CHs 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 poor to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 21-22 due to weak effects from CH536.

Coronal holes (1) Coronal mass ejection (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. 0.5k 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 magnetic polarity overlay
Comment
SWPC STAR SDO SWPC STAR Current Previous
2K 1K
11569 2012.09.09
2012.09.10
2 1 1 S12W70 0170 HSX HSX  
11571 2012.09.10
2012.09.12
3 7 5 S14W46 0050 CAO CRO area: 0060
S1912 2012.09.12       N14W26           plage
S1914 2012.09.13       N20W21           plage
S1915 2012.09.13       N23W41           plage
11573 2012.09.15
2012.09.16
  8 3 N19E08 0010   BXO location: N18E14
11574 2012.09.16 4 6 4 S22W70 0040 CAO DSO location: S23W68
S1922 2012.09.16       N15W39           plage
11575 2012.09.17
2012.09.18
6 9 5 N07E50 0280 EKO EKO

area: 0420

S1924 2012.09.17   1   S22E14 0000   AXX  
S1925 2012.09.17       S12E01           plage
11576 2012.09.18
2012.09.19
3 7 4 S21E52 0070 DSO DSO  
S1927 2012.09.19   7 2 N20E68 0020   BXO  
S1928 2012.09.20   2 2 N02E14 0010   BXO    
Total spot count: 18 48 26  
Sunspot number: 68 138 106  (total spot count + 10 * number of spotted regions)
Weighted SN: 48 76 54  (Sum of total spot count + classification weighting for each AR. Classification weighting: X=0, R=3, A/S=5, H/K=10)
Relative sunspot number (Wolf number): 41 48 55 k * (sunspot number). k = 0.6 for SWPC, k = 0.35 for STAR SDO 2K, k = 0.55 for STAR SDO 1K

Monthly solar cycle data

Month Average measured solar flux International sunspot number (SIDC) Smoothed sunspot number Average ap
(3)
2011.05 95.8 41.5 47.6 (+5.8) 8.94
2011.06 95.8 37.0 53.2 (+5.6) 8.06
2011.07 94.2 43.8 57.2 (+4.0) 8.16
2011.08 101.7 50.6 59.0 (+1.8) 7.26
2011.09 133.8 78.0 59.5 (+0.5) 12.27
2011.10 137.3 88.0 59.9 (+0.4) 8.28
2011.11 153.5 96.7 61.1 (+1.2) 5.55
2011.12 141.3 73.0 63.4 (+2.3) 3.78
2012.01 132.5 58.3 65.5 (+2.1) 7.15
2012.02 106.5 32.9 66.9 (+1.4) 8.81
2012.03 114.7 64.3 (67.3 projected, +0.4) 16.08
2012.04 113.0 55.2 (66.5 projected, -0.8) 10.10
2012.05 121.5 69.0 (64.4 projected, -2.1) 7.06
2012.06 119.6 64.5 (63.6 projected, -0.8) 10.08
2012.07 133.9 66.5 (64.6 projected, +1.0) 13.90
2012.08 115.4 63.1 (67.2 projected, +2.6) 7.96
2012.09 117.7 (1)  56.0 (2A) / 84.1 (2B) / 58.3 (2C) (70.0 projected, +2.8) (11.41)

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. 2C) STAR SDO 1K Wolf number month to date.
3) Running average based on the quicklook and definitive Potsdam WDC ap indices. Values in red are based on the definitive international Potsdam WDC 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.