Solar Terrestrial Activity Report

Last major update issued on December 20, 2009 at 05:20 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update October 4, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update October 4, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update October 4, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update September 13, 2009)]

The geomagnetic field was inactive on December 19. Solar wind speed ranged between 363 and 447 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 81.7. The planetary A index was 1 (STAR Ap - based on the mean of three hour interval ap indices: 0.8). Three hour interval K indices: 00000000 (planetary), 00110100 (Boulder).

The background x-ray flux is at the class A9 level.

At midnight there were 2 spotted regions on the visible solar disk.

Region 11035 decayed slowly and was mostly quiet. C flares are still possible. Flare: C2.9 at 00:14 UTC
New region 11036 emerged in the southwest quadrant.

December 17-19: No partially or fully Earth directed CMEs were observed in LASCO or STEREO imagery.
December 16: A partial halo CME was observed in LASCO images after a C5 event early in the day in region 11035. STEREO images confirms that this CME is Earth directed.

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

No obvious coronal holes are currently in or near Earth facing positions.

Processed SOHO/EIT 195 image at 23:48 UTC on December 18. The darkest areas on the solar disk are likely coronal holes.

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is good. Propagation on long distance northeast-southwest paths is poor.

The geomagnetic field is expected to be quiet to active on December 20 due to a likely impact from a CME observed on December 16. Quiet to unsettled conditions are likely on December 21, becoming quiet on December 22-23.

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.

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/SWPC. 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 SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers.

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/SWPC) 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.