Solar Terrestrial Activity Report

Last major update issued on August 12, 2006 at 05:10 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 11. Solar wind speed ranged between 410 and 485 km/s (all day average 452 km/s - increasing 7 km/s over the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 803.9. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.0).
Three hour interval K indices: 21212222 (planetary), 11222212 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was low. A total of 4 C class events was recorded during the day.

Region 10904 became magnetically simpler as the central and leading negative polarity spots merged and the separation between the opposite polarity areas increased. The region is still large and could produce an M class flare. Flares: C2.8 at 00:41, C2.1 at 08:04, C1.3 at 09:42 and a long duration C1.1 event peaking at 12:44 UTC.

Coronal mass ejections (CMEs)

August 9-11: 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

No obvious coronal holes are currently in or approaching Earth facing positions.

Processed SOHO/EIT 284 image at 01:06 UTC on August 12. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet on August 11-15.

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 to fair. Several stations from the easternmost parts of North America were audible, some with good signals. 1370 WDEA and 1410 WPOP were both fairly weak while 1060 WBIX was surprisingly strong. Propagation on long distance northeast-southwest paths is poor to fair with the only the most common Argentine stations (like 1030 and 1190 kHz) heard with good signals.

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.