Solar Terrestrial Activity Report

Last major update issued on September 22, 2006 at 04:05 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 on September 21. Solar wind speed ranged between 287 and 348 km/s (all day average 307 km/s - decreasing 93 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 71.4. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.2). Three hour interval K indices: 01110122 (planetary), 11122220 (Boulder).

The background x-ray flux is ar 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 added a few tiny spots. Polarities are mixed within this region and there is a chance of a C class flare.

Coronal mass ejections (CMEs)

September 19-21: 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) has rotated into view at the east limb and will likely be in an Earth facing position on September 26-27.

Processed SOHO/EIT 284 image at 19:06 UTC on September 21. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be mostly quiet on September 22 becoming unsettled to minor storm on September 23-24 due to a high speed stream from CH240. Quiet to unsettled is likely on September 25 with mostly quiet conditions on September 26-28.

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 fair. Strong signals were noted from stations like 850 WEEI, 1130 WBBR and 1510 WWZN. A few stations from Cuba, Venezuela and Colombia had good signals as well. Propagation on long distance northeast-southwest paths is 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.