Solar Terrestrial Activity Report

Last major update issued on September 24, 2006 at 02:30 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 active on September 23. Solar wind speed ranged between 277 and 432 km/s (all day average 328 km/s - increasing 33 km/s over the previous day). A high speed stream from CH240 began influencing the geomagnetic field during the morning and slowly intensified during the day. The average solar wind density for the day is one of the highest recorded in SOHO history.

Solar flux measured at 20h UTC on 2.8 GHz was 70.4. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.1). Three hour interval K indices: 01211134 (planetary), 02222334 (Boulder).

The background x-ray flux is far below the class A1 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 10910 decayed slowly and was mostly quiet.

Coronal mass ejections (CMEs)

September 21-23: 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 (CH240) was in an Earth facing position on September 20-21. A recurrent coronal hole (CH241) in the southern hemisphere will likely be in an Earth facing position on September 25-27.

Processed SOHO/EIT 284 image at 19:06 UTC on September 22. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to major storm on September 24 due to a high speed stream from CH240 and quiet to active on September 25. Mostly quiet conditions are likely on September 26-27. Quiet to minor storm conditions are again likely on September 28-30 due to a high speed stream from CH241.

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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor to poor. Propagation was at times very poor with very weak signals from a few stations, then sometimes poor with fair signals from the most often heard Newfoundland stations. Propagation on long distance northeast-southwest paths is fair.

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
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10910 2006.09.18 3 5 S10W18 0020 CRO  
Total spot count: 3 5  
SSN: 13 15  

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 79.3 (1) 19.1 (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]