Solar Terrestrial Activity Report

Last major update issued on September 24, 2007 at 04:55 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update July 23, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 23, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 23, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update July 1, 2007)]

Recent activity

The geomagnetic field was quiet to active on September 23. Solar wind speed ranged between 568 and 710 km/s (average speed was 615 km/s, increasing 39 km/s over the previous day) under the influence of a high speed stream from CH291.

Solar flux measured at 20h UTC on 2.8 GHz was 66.3. The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 14.8). Three hour interval K indices: 34422123 (planetary), 34432113 (Boulder).

The background x-ray flux is below the class A1 level.

At midnight the visible solar disk was spotless (consecutive days: 17). The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

September 21-23: No obvious fully or partly Earth directed CMEs were observed 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 large, recurrent trans equatorial coronal hole (CH291) was in an Earth facing position on September 16-21. A recurrent coronal hole (CH292) in the southern hemisphere will rotate into an Earth facing position on September 24.

Processed STEREO 195 image at 21:25 UTC on September 23. The darkest areas on the solar disk are likely coronal holes.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to very poor. Propagation on long distance northeast-southwest paths is fair to good.

Monitoring remarks from a location near N58E06: September 23: At 04h UTC a number of stations from the Canadian Atlantic provinces and the east coast of the USA were audible at fair signal levels. Most of these stations disappeared when the current disturbance intensified over the next couple of hours. Instead lots of stations from Venezuela, Colombia and Puerto Rico were heard. Some had excellent signals, like 880 Venezuela Guyana and 940 WIPR.


The geomagnetic field is expected to be quiet to active on September 24 due to a high speed stream from CH291. Mostly quiet conditions are likely on September 25-26. A high speed stream from CH292 is likely to arrive either on September 27 or 28 and cause some unsettled and 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 (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
Total spot count: 0 0  
SSN: 0 0  

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)
2006.07 75.7 12.2 15.3 (-1.0)
2006.08 79.0 12.9 15.6 (+0.3)
2006.09 77.8 14.4 15.6 (+0.0)
2006.10 74.3 10.4 14.2 (-1.4)
2006.11 86.3 21.5 12.7 (-1.5)
2006.12 84.5 13.6 12.1 (-0.6)
2007.01 83.3 16.9 12.0 (-0.1)
2007.02 77.7 10.6 11.6 (-0.4)
2007.03 72.2 4.8 (11.1 predicted, -0.5)
2007.04 72.4 3.7 (10.7 predicted, -0.4)
2007.05 74.4 11.7 (10.2 predicted, -0.5)
2007.06 73.7 12.0 (10.0 predicted, -0.2)
2007.07 71.6 10.0 (10.0 predicted, +0.0)
2007.08 69.1 6.2 (10.3 predicted, +0.3)
2007.09 67.2 (1) 3.2 (2) (11.5 predicted, +1.2)

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]