Solar Terrestrial Activity Report

Last major update issued on October 20, 2006 at 04:35 UTC.

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

Recent activity

The geomagnetic field was very quiet on October 19. Solar wind speed ranged between 283 and 314 km/s (all day average 289 km/s - decreasing 16 km/s from the previous day). The beginning of the high speed stream from CH244 was observed at ACE at 23h UTC. Since then the wind speed has increased to the 350-400 km/s range. The geomagnetic effects so far have been minor as the interplanetary magnetic field has been northwards.

Solar flux measured at 20h UTC on 2.8 GHz was 69.6. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.3). Three hour interval K indices: 01011001 (planetary), 12012221 (Boulder).

The background x-ray flux is 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.

New region 10917 emerged near the center of the visible disk.

Coronal mass ejections (CMEs)

October 17-19: 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 well defined large, recurrent trans equatorial coronal hole (CH244) was in an Earth facing position on October 16-18. The remains of CH241 have rotated into view in the southeastern quadrant.

Processed SOHO/EIT 284 image at 01:06 UTC on October 20. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to major storm on October 20-21 and quiet to unsettled on October 22-23. Mostly quiet conditions are likely for the remainder of the month as the recurrent coronal hole CH241 has decayed substantially and at this time appears to be outside of the potentially geoeffective latitudes.

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. Propagation on long distance northeast-southwest paths is poor.

Monitoring remarks from a location near N58E05: Quite a few stations from the easternmost parts of North America were audible early in the night with the best signals below 1100 kHz. At 04h UTC only a few stations from North America were audible, instead stations from Venezuela and Colombia were dominant on several frequencies in the lower part of the MW band.

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.