Solar Terrestrial Activity Report

Last major update issued on October 12, 2007 at 03:55 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update October 4, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update October 4, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update October 4, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update October 3, 2007)]

Recent activity

The geomagnetic field was very quiet on October 11. Solar wind speed ranged between 274 and 288 km/s (average speed was 280 km/s, decreasing 9 km/s from the previous day). A low speed stream associated with CH294 began to influence the geomagnetic field early on October 12.

Solar flux measured at 20h UTC on 2.8 GHz was 68.8. The planetary A index was 1 (STAR Ap - based on the mean of three hour interval ap indices: 0.8). Three hour interval K indices: 00000001 (planetary), 00000001 (Boulder).

The background x-ray flux is below the class A1 level.

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

October 9-11: No obvious fully or partly Earth directed CMEs were observed 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 coronal hole (CH294) in the southern hemisphere was in an Earth facing position on October 8-10. CH294 has become better defined over the last solar rotation, although most of the coronal hole is too far to the south to influence Earth. A recurrent trans equatorial hole (CH295) will likely rotate into an Earth facing position on October 14-17. CH295 is poorly defined in the western part. The development of an active region in the southeastern part of the coronal hole has diminished its area significantly.

Processed SOHO/EIT 195 image at 02:13 UTC on October 12. The darkest areas on the solar disk are likely coronal holes.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is good. Propagation on long distance northeast-southwest paths is poor.

Monitoring remarks from a location near N58E06: October 12: Many stations from North America were audible during the night, some with strong signals. While nothing new was logged 1290 CJBK and 1390 WNIO were both unusually good. The best Trans Atlantic propagation sector was 280-310 degrees.

Forecast

The geomagnetic field is expected to be mostly quiet October 12-16, a few unsettled intervals are possible on October 12-13 due to effects from CH294. Some unsettled to active intervals are likely on October 17-21 due to a high speed stream from CH295.

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.

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.