Solar Terrestrial Activity Report

Last major update issued on October 21, 2006 at 02:50 UTC. (Charts not updated today)

[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 quiet to unsettled on October 20. Solar wind speed ranged between 308 and 537 km/s (all day average 372 km/s - increasing 83 km/s over the previous day) under the influence of a high speed stream from CH244. The disturbance associated with CH244 has been less geoeffective than would normally be expected from the observed ACE data. The average solar wind density for the day was very high.

Solar flux measured at 20h UTC on 2.8 GHz was 71.1. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.5). Three hour interval K indices: 20123333 (planetary), 21223433 (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.

Region 10917 developed slowly and was quiet.

Coronal mass ejections (CMEs)

October 18-20: 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 southernmost extensions of a new coronal hole in the northern hemisphere rotated across the central meridian on October 20-21. The remains of CH241 have rotated into view in the southeastern quadrant, apparently outside of potentially geoeffective latitudes.

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


The geomagnetic field is expected to be quiet to minor storm on October 21 and quiet to unsettled on October 22-24. Mostly quiet conditions are likely for the remainder of the month as the recurrent coronal hole CH241 has decayed substantially.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)

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.


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: Stations from Newfoundland and Nova Scotia had fair to good signals most of the night. From the USA only a few stations from the northeast were audible. 1470 CPN Radio (Perú) was strong at 02:30 UTC.

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.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10917 2006.10.19 5 4 S05W20 0030 BXO classification was CAO at midnight
Total spot count: 5 4  
SSN: 15 14  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2005.08 90.5 36.4 27.4 (-1.7)
2005.09 91.1 21.9 25.8 (-1.6)
2005.10 77.0 8.7 25.5 (-0.3)
2005.11 86.3 18.0 24.9 (-0.6)
2005.12 90.7 41.1 23.0 (-1.9)
2006.01 83.4 15.3 20.8 (-2.2)
2006.02 76.5 4.9 18.6 (-2.2)
2006.03 75.4 10.6 17.3 (-1.3)
2006.04 89.0 30.2 (17.1 predicted, -0.2)
2006.05 80.9 22.2 (16.8 predicted, -0.3)
2006.06 76.5 13.9 (15.1 predicted, -1.7)
2006.07 75.7 12.2 (13.2 predicted, -1.9)
2006.08 79.0 12.9 (12.8 predicted, -0.4)
2006.09 77.8 14.5 (12.6 predicted, -0.2)
2006.10 73.9 (1) 8.5 (2) (11.6 predicted, -1.0)

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.

[DX-Listeners' Club]