Solar Terrestrial Activity Report

Last major update issued on September 11, 2005 at 03:45 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update September 3, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 3, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 3, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update September 2 , 2005)]

Recent activity

The geomagnetic field was quiet to minor storm on September 10. Solar wind speed ranged between 424 and 745 (all day average 605) km/sec. A solar wind shock was observed at ACE near 01h UTC on September 11. Solar wind speed increased to near 1000 km/sec at SOHO as the CME associated with the X6 event in region 10808 on September 9 arrived. The transit time was only 29 hours.

Solar flux measured at 20h UTC on 2.8 GHz was 116.0. The planetary A index was 30 (STAR Ap - based on the mean of three hour interval ap indices: 30.4).
Three hour interval K indices: 22534555 (planetary), 22534544 (Boulder).

The background x-ray flux is at the class C2 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was high. A total of 3 C, 7 M and 2 X class events was recorded during the day.

Region 10808 changed a lot on September 10. Some decay was observed in the northern and eastern sections while new spots emerged to the southwest of the main penumbra. The region is not as compact as it was as the previously huge penumbra has split into several smaller penumbrae. There is still a very strong magnetic delta structure within the main penumbra. Further proton X class flares are likely. Flares: M1.7 at 01:54, M1.1 at 04:51, M1.2 at 06:02, M3.7/2N at 06:14, M1.9/1F at 09:07, C7.6 at 10:28, C7.8/1F at 13:47, C7.1 at 15:50, X1.1 at 16:43, M4.1/1N at 19:36, X2.1 long duration event peaking at 22:30 and M8.7 at 23:01 UTC. Moderate type II and IV radio sweeps were associated with the X2 event, as was a fast, full halo CME.
Region 10809 was quiet and stable.

Coronal mass ejections (CMEs)

September 9: LASCO C2 and C3 images are again available, however, they are strongly contaminated by the ongoing proton storm. Several CMEs (where the main body of the ejected material is not aimed at Earth) are likely to have been produced by the multitude of M and X class events in region 10808. Glancing impacts are possible on September 11. The CME associated with the long duration X6 event is likely to be more significant than the others.
September 10: Another large, fast full halo CME was associated with the X2 long duration event in region 10808 late in the day.

Coronal holes

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

A recurrent trans equatorial coronal hole (CH187) will rotate to an Earth facing position on September 9-11.

Processed TRACE mosaic image on September 6, 2005. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be active to major storm on September 11. The full halo CME observed on September 10 should reach Earth early on September 12 and cause active to severe storm conditions. Unsettled to major storm conditions are likely on September 13.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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) Material from a CME is likely to impact 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.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is useless. Propagation on long distance northeast-southwest paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. Quite a few stations from Argentina were heard with fair to good signals from 950 Radio Belgrano, 1070 Radio El Mundo and 1190 Radio América.

Active solar regions (Recent map)

Compare to the previous day's image.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SEC. 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 SEC or where SEC has observed no spots. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10808 2005.09.07 38 41 S09E44 1400 EKC beta-gamma-delta
10809 2005.09.08 1 2 N10E34 0020 HSX  
S591 2005.09.09     S05E12     plage
Total spot count: 39 43  
SSN: 59 63  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 35.9 (-1.6)
2004.11 113.2 43.5 35.3 (-0.6)
2004.12 94.5 17.9 35.2 (-0.1)
2005.01 102.2 31.3 34.6 (-0.6)
2005.02 97.2 29.2 33.9 (-0.7)
2005.03 89.9 24.5 (33.5 predicted, -0.4)
2005.04 86.0 24.4 (32.2 predicted, -1.3)
2005.05 99.3 42.6 (29.9 predicted, -2.3)
2005.06 93.7 39.6 (28.7 predicted, -1.2)
2005.07 96.4 39.9 (27.7 predicted, -1.0)
2005.08 90.5 36.4 (25.8 predicted, -1.9)
2005.09 86.5 (1) 8.9 (2) (24.2 predicted, -1.6)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically 30-50% lower.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.

[DX-Listeners' Club]