Solar Terrestrial Activity Report

Last major update issued on December 15, 2006 at 05:50 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update November 12, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update November 12, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update November 12, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update November 12, 2006)]

Recent activity

The geomagnetic field was quiet to very severe storm on December 14. Solar wind speed ranged between 553 and 992 km/s (all day average 730 km/s - increasing 112 km/s over the previous day). A very strong solar wind shock was observed at SOHO at 13:56 UTC with a sudden increase in wind speed from 624 to 963 km/s. Since then the geomagnetic field has been at major to very severe storm levels. The peak 3-hour planetary A index was recorded 00-03h UTC on December 15 reaching 236.

Solar flux measured at 20h UTC on 2.8 GHz was 93.4. The planetary A index was 63 (STAR Ap - based on the mean of three hour interval ap indices: 63.4). Three hour interval K indices: 21226768 (planetary), 22335647 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was high. A total of 2 C and 1 X class events was recorded during the day.

Region 10930 decayed and lost much of the penumbral area in the southern part of the single penumbra. Actually the penumbra appears to be splitting. If that happens the chance of an additional major flare will decrease dramatically. Flares: C1.0 at 12:10, C1.2 at 16:49 ant a major X1.5 long duration proton event peaking at 22:15 UTC. Moderate type II and IV radio sweeps were recorded during the X1.5 event.

Coronal mass ejections (CMEs)

December 12: No obvious partly or fully Earth directed CMEs were detected in LASCO imagery.
December 13: A fast full halo CME was observed shortly after the X3 flare.
December 14: No LASCO images after 15h UTC are currently available. The X1 event mentioned above was likely associated with a CME.

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

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

Processed SOHO/EIT 284 image at 01:38 UTC on December 14. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be active to very severe storm on December 15. Effects from a CME associated with the X1.5 flare on December 14 could reach Earth on December 16 and cause active to major storm conditions, possibly extending into December 17. On December 19-21 effects from CH252 will likely cause unsettled to minor storm conditions.

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 useless. Propagation on long distance northeast-southwest paths is very poor to useless.

Monitoring remarks from a location near N58E06: No trans Atlantic stations were heard. Propagation was very auroral with weak signals from northern Europe and strong signals from the south. On 639 kHz there were no less than 3 RNE (Spain) stations (noticed because of significant time lag between the 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.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10929 2006.12.04     N03W63     plage
10930 2006.12.04 13 8 S05W47 0620 DKC beta-gamma-delta
Total spot count: 13 8  
SSN: 23 18  

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) 16.8 (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]