Solar Terrestrial Activity Report

Last major update issued on August 26, 2006 at 05:40 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update August 6, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update August 6, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update August 6, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update August 6, 2006)]

Recent activity

The geomagnetic field was quiet on August 25. Solar wind speed ranged between 334 and 354 km/s (all day average 347 km/s - decreasing 89 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 77.2. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.5). Three hour interval K indices: 11011101 (planetary), 10000001 (Boulder).

The background x-ray flux is at the class A4 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 10905 decayed slightly with several small trailing spots disappearing and the trailing penumbra taking on a symmetrical shape. The large leading penumbra appears to be splitting into two smaller penumbrae.

Coronal mass ejections (CMEs)

August 23-25: No 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 fairly large trans equatorial coronal hole (CH237) will likely rotate into an Earth facing location on August 24-26.

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 quiet on August 26. Quiet to minor storm conditions are possible on August 27-29 due to effects from CH237.

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 poor. Only weak signals were heard from North America as propagation was significantly worse than expected. Stations from Venezuela (in particular on 1290, 1310, 1390, 1470 and 1500 kHz) had the best signals. Propagation on long distance northeast-southwest paths is fair with some stations from Argentina (notably on 700, 710, 870 and 1190 kHz) reaching good to excellent signal levels in peaks.

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.