Solar Terrestrial Activity Report

Last major update issued on September 12, 2006 at 02:35 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 quiet to unsettled on September 11. Solar wind speed ranged between 326 and 388 km/s (all day average 351 km/s - increasing 4 km/s over the previous day). A weak disturbance was in progress during the first half of the day.

Solar flux measured at 20h UTC on 2.8 GHz was 84.6. The planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 8.5). Three hour interval K indices: 33322101 (planetary), 33322112 (Boulder).

The background x-ray flux is at the class A5 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was low. A single C class event was recorded during the day.

Region 10908 was mostly quiet and stable. Flare: C1.0 at23:09 UTC.
Region 10909 decayed further and could soon become spotless.

Coronal mass ejections (CMEs)

September 9-11: No obvious partly or fully Earth directed CMEs were detected in incomplete 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 coronal hole (CH239) in the southern hemisphere will likely rotate into an Earth facing position on September 13-14.

Processed SOHO/EIT 284 image at 19:08 UTC on August 18. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be mostly quiet on September 12-15. Coronal hole effects are likely on September 16-17.

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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is good. Many stations from the eastern US and Canada were audible during the night (after 2330 UTC)with the best signals coming from the northeastern USA. 1060 WBIX, 1390 WEGP and 1470 WLAM were all heard with excellent signals. 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.

Monthly solar cycle data

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.