Solar Terrestrial Activity Report

Last major update issued on September 30, 2011 at 04:40 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 27, 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 to active on September 29. Solar wind speed ranged between 429 and 587 km/s under the influence of CME effects.

Solar flux measured at 23h UTC on 2.8 GHz was 136.6 (increasing 21.2 over the last solar rotation). The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 15.4). Three hour interval K indices: 44334111 (planetary), 65432322 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight UTC the visible solar disk had 6 spotted regions (in 2K resolution SDO images).

Region 11301 [N17W63] decayed further and was quiet.
Region 11302 [N13W19] had the leader penumbra splitting into two large penumbrae. There's a weak magnetic delta structure in the southern part of the current leading penumbra and a more significant delta at the southeast side of the largest penumbra. The region was mostly quiet but still has major flare potential. Flare: C2.7 long duration event peaking at 12:47 UTC
Region 11304 [N14W45] decayed significantly and was quiet.
Region 11305 [N12E15] developed further and could produce a minor M class flare. Flares: C1.3 at 10:23, C5.6 at 18:05 UTC. The latter event was interesting as it seemed to trigger a filament eruption south of the region. LASCO and STEREO images will require further analysis as they are inconclusive as to whether or not a potentially geoeffective CME was produced. The region was the source of a C7.7 flare at 04:00 UTC on September 30.
Region 11306 [N14E35] was quiet and stable.
Region 11307 [N15E65] was quiet and stable.

Coronal mass ejections (CMEs)

September 27-28: No obviously Earth directed CMEs observed.
September 29: Uncertain pending further analysis for the C5.6 event in region 11305.

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 was in an Earth facing position on September 28-29.

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 poor.

Forecast

The geomagnetic field is expected to be quiet on September 30. Weak effects from CH477 are possible on October 1-2 resulting in quiet to unsettled conditions with a chance of active intervals.

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
11301 2011.09.17
2011.09.18
1 2 N16W64 0020 HSX HRX

 

11302 2011.09.21
2011.09.22
23 36 N13W16 0750 FKC FKC beta-gamma-delta

area: 1100

11304 2011.09.24 2 4 N13W44 0010 BXO BXO  
11305 2011.09.24
2011.09.25
8 16 N13E16 0100 CSO CSI area: 0200
S1233 2011.09.24     N19W50           plage
11306 2011.09.25
2011.09.26
1 2 N14E34 0030 HSX HSX  
S1235 2011.09.25     N18W35           plage
S1236 2011.09.26     S17W10           plage
S1237 2011.09.26     N13W56           plage
11307 2011.09.27
2011.09.28
4 8 N16E65 0010 BXO DRO area: 0030
S1239 2011.09.27     S22E06           plage
S1240 2011.09.27     N25W34          
Total spot count: 39 68  
Sunspot number: 99 128  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 64 94  (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): 59 42  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
2011.09 133.6 (1) 103.8 (2A) /  107.4 (2B) (56.7 predicted, +2.3) (12.97)

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.