Solar Terrestrial Activity Report

Last major update issued on December 19, 2005 at 05:05 UTC.

The next full update will likely be on January 4, 2006. Occasional partial updates will be posted when possible.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update December 6, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update December 6, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update December 6, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update December 3, 2005)]

Recent activity

The geomagnetic field was inactive to very quiet on December 18. Solar wind speed ranged between 276 and 365 (all day average 333) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 85.6. The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.9).
Three hour interval K indices: 10011001 (planetary), 21121001 (Boulder).

The background x-ray flux is at the class A5 level.

At midnight there were 4 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10834 decayed slowly and quietly.
Region 10835 was quiet and stable.
Region 10837 developed quickly and could produce at least C flares.

Spotted regions not numbered by NOAA/SEC:
[S614] This region rotated into view on December 18 at the northeast limb. Location at midnight: N17E74

Coronal mass ejections (CMEs)

December 16-18: No obvious partly or fully Earth directed CMEs were observed.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report with the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH201) in the southern hemisphere was likely in an Earth facing position on December 17.

Processed SOHO/EIT 284 image at 20:23 UTC on December 18. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be mostly quiet on December 19-20 with some unsettled and active intervals possible on December 21 due to effects from CH201.

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) Material from a CME is likely to impact 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 fair to good. Propagation on long distance northeast-southwest paths is very poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and WLAM Lewiston ME. Propagation was best towards the US east coast and Venezuela/Colombia. Propagation on December 18 became very good during the hours before and after LSR. Several stations from Mexico were noted and some stations located near the big lakes had good signals in peaks.

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.