Solar Terrestrial Activity Report

Last major update issued on December 14, 2006 at 05:40 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 unsettled on December 13. Solar wind speed ranged between 568 and 767 km/s (all day average 618 km/s - decreasing 83 km/s from the previous day) under the influence of a high speed stream from CH251.

Solar flux measured at 20h UTC on 2.8 GHz was 93.6. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.6). Three hour interval K indices: 23000002 (planetary), 34112112 (Boulder).

The background x-ray flux is at the class B1 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 developed slowly in the southern part of the main penumbra as a few positive polarity spots emerged while slow decay was observed in the northern negative polarity section. Further major flares are possible as long as the current magnetic delta structure persists. Flares: major X3.4/4B proton flare peaking at 02:40, C2.2 at 14:23 and C1.7 at 18:25 UTC.

Coronal mass ejections (CMEs)

December 11-12: 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.

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.

Forecast

The geomagnetic field is expected to be quiet initially on December 14, then, sometime during the latter half of the day and on December 15, range from active to severe storm conditions due to CME effects. Quiet to active conditions are likely on December 16.

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

Monitoring remarks from a location near N58E06: No North American stations were heard. A few of the more common Puerto Rican stations (1320 Radio Isla and 1480 Onda Tropical) and 1290 Radio Puerto Cabello (Venezuela) were present; otherwise another very poor night for TA 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.

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.