Solar Terrestrial Activity Report

Last major update issued on September 17, 2006 at 06:35 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, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 3, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 3, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update September 8, 2006)]

Recent activity

The geomagnetic field was inactive to quiet on September 16. Solar wind speed ranged between 286 and 348 km/s (all day average 314 km/s - decreasing 5 km/s from the previous day). A low speed stream from CH239 arrived near 16h UTC and the solar wind speed has increased slowly since then. The interplanetary magnetic field has been weakly southwards since early on September 17.

Solar flux measured at 20h UTC on 2.8 GHz was 79.2. The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.3). Three hour interval K indices: 00001122 (planetary), 10012111 (Boulder).

The background x-ray flux is at the class A3 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10908 decayed slowly and quietly and will rotate over the southwest limb today.

Spotted regions not numbered by NOAA/SEC:
[S675] This region rotate into view at the southeast limb on September 16. Location at midnight: S09E74.

Coronal mass ejections (CMEs)

September 14-16: No obvious partly or fully Earth directed CMEs were detected in LASCO imagery.

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 (CH239) was in an Earth facing position on September 13-14. A recurrent trans equatorial coronal hole (CH240) will likely rotate into an Earth facing position on September 20-22.

Processed SOHO/EIT 284 image at 22:15 UTC on September 16. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on September 17-18 under the influence of effects from CH239. Quiet to unsettled conditions are likely on September 19-22 becoming unsettled to minor storm on September 23-24 due to a high speed stream from CH240.

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.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is fair. Many stations from the eastern parts of North America had fair to good signals, however, propagation was not as good as after LSR on September 16 when signals from the central and western parts of North America were audible. Then stations like 1470 CJVB and 1510 KGA were heard well above signals from further east. Propagation on long distance northeast-southwest paths is very poor.

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
10908 2006.09.05 3 2 S13W73 0190 HSX classification was HAX at midnight, area 0120
S675 2006.09.16   1 S09E74 0040 HSX  
Total spot count: 3 3  
SSN: 13 23  

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)
2005.07 96.4 40.1 29.1 (+0.3)
2005.08 90.5 36.4 27.4 (-1.7)
2005.09 91.1 21.9 25.8 (-1.6)
2005.10 77.0 8.5 25.5 (-0.3)
2005.11 86.3 18.0 24.9 (-0.6)
2005.12 90.7 41.2 23.0 (-1.9)
2006.01 83.4 15.4 20.8 (-2.2)
2006.02 76.5 4.7 18.6 (-2.2)
2006.03 75.4 10.8 (17.1 predicted, -1.5)
2006.04 89.0 30.2 (16.4 predicted, -0.7)
2006.05 80.9 22.2 (15.9 predicted, -0.5)
2006.06 76.5 13.9 (14.1 predicted, -1.8)
2006.07 75.7 12.2 (12.4 predicted, -1.7)
2006.08 79.0 12.9 (11.9 predicted, -0.5)
2006.09 82.1 (1) 16.3 (2) (11.9 predicted, -0.0)

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]