Solar Terrestrial Activity Report

Last major update issued on December 13, 2006 at 04:20 UTC. Very significant proton flare in progress!

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[Archived reports (last update November 12, 2006)]

Recent activity

The geomagnetic field was unsettled to minor storm on December 12. Solar wind speed ranged between 595 and 868 km/s (all day average 701 km/s - increasing 46 km/s over the previous day) under the influence of a high speed stream from CH251.

Solar flux measured at 20h UTC on 2.8 GHz was 102.0. The planetary A index was 26 (STAR Ap - based on the mean of three hour interval ap indices: 26.1). Three hour interval K indices: 35334354 (planetary), 25334344 (Boulder).

The background x-ray flux is at the class B6 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 10930 changed as the positive polarity spots in the southern part of the main penumbra rotated eastwards. The magnetic delta structure became stronger. Further major flares are possible.

Region 10930 produced a major X3.4/4B proton flare peaking at 02:40 UTC on December 13. 4B is the maximum brightness on the brightness scale and occurs very rarely. Strong type II and IV radio sweeps were recorded and an intense proton storm started at Earth soon after the flare. It is likely that a major very fast Earth directed CME was caused by the flare.

Coronal mass ejections (CMEs)

December 10-12: 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

CH251 was in an Earth facing position on December 7-9. Recurrent coronal hole CH252 (southern hemisphere) will likely rotate into an Earth facing position on December 16-17.

Processed SOHO/EIT 195 image at 00:48 UTC on December 13. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on December 13 due to coronal hole effects. A CME impact (associated with the X3 flare early on December 13) is likely sometime after 06h UTC on December 14. Expect minor to very severe geomagnetic storm conditions for 24-36 hours after the impact. The intense proton event in progress will strongly degrade radio communication over polar  and near polar paths. Low and medium frequency propagation could remain very poor until after Christmas.

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 was poor until 03h, then became very poor to useless. Propagation on long distance northeast-southwest paths is very poor.

Monitoring remarks from a location near N58E06: Some of the common east coast North American stations were noted before 03h UTC, as were stations from the Caribbean and northern South America. Cuba on 890 kHz had the best signal. At 04h UTC there was no audio from any TA stations.

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
10929 2006.12.04     N03W37     plage
10930 2006.12.04 17 18 S06W21 0680 DKI beta-gamma-delta
Total spot count: 17 18  
SSN: 27 28  

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)
2005.09 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 (-0.2)
2006.05 80.9 22.2 17.3 (+0.2)
2006.06 76.5 13.9 (16.3 predicted, -1.0)
2006.07 75.7 12.2 (14.7 predicted, -1.6)
2006.08 79.0 12.9 (14.2 predicted, -0.5)
2006.09 77.8 14.5 (14.1 predicted, -0.1)
2006.10 74.3 10.4 (13.0 predicted, -1.1)
2006.11 86.3 21.5 (11.5 predicted, -1.5)
2006.12 94.0 (1) 15.4 (2) (11.3 predicted, -0.2)

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]