Solar Terrestrial Activity Report

Last major update issued on December 6, 2006 at 04:15 UTC. Minor update posted at 19:00 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 on December 5. Solar wind speed ranged between 280 and 417 km/s (all day average 340 km/s - increasing 33 km/s over the previous day). Solar wind speed increased slowly after noon as the stream associated with CH250 arrived. A geomagnetic disturbance began early on Dec.6.

Solar flux measured at 20h UTC on 2.8 GHz was 102.4. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 1.8). Three hour interval K indices: 00000112 (planetary), 00012212 (Boulder).

The background x-ray flux is at the class B7 level.

At midnight there were 3 spotted regions on the visible solar disk. The solar flare activity level was high. A total of 9 C, 1 M and 1 X class events was recorded during the day.

Region 10926 decayed slowly and quietly.
Region 10927 was quiet and stable.
Region 10930 is a complex region capable of producing further major flares. There is a magnetic delta structure in the northwestern part where negative polarity is nearly embedded within a strong positive polarity area. Flares: C2.2 at 02:03, C3.9 at 05:09, C4.2 at 06:26, M1.8 at 08:03, C1.5 at 09:11, major X9.0/2N at 10:35 (associated with a strong type II and a moderate type IV radio sweep), C1.7 at 16:15, C1.2 at 17:22, C5.8 at 20:07, C3.7 at 20:54 and C1.5 at 23:55 UTC. The X9 flare was associated with a minor increase in proton levels. An X9 flare at this stage of a solar cycle is very unusual and seems to have caused problems for some instruments on GOES-13. This is an image from GOES-13 a few minutes after the flare peak (and shortly before imaging problems were noticed):

Comment added at 19:00 UTC on December 6: Region 10930 produced an X6.5 flare at 18:47 UTC. Earlier today, at 08:23 UTC, this region was the source of another major flare, an M6.0 event. Proton levels are increasing and a proton event has begun. Region 10930 is quickly becoming one of the most significant flare producers of solar cycle 23.

Coronal mass ejections (CMEs)

December 3-4: No obvious partly or fully Earth directed CMEs were detected in very incomplete LASCO imagery.
December 5: While no LASCO images are available from the time after the X9 event, such events are often associated with large and fast CMEs, so there is at least a chance of a flank impact from the CME produced by the event.

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

A recurrent coronal hole (CH250) in the southern hemisphere was in an Earth facing position on December 3-4.

Processed SOHO/EIT 284 image at 19:06 UTC on November 24. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to minor storm on December 6-7 with a chance of major storm intervals due to effects from CH250. Additionally there is a chance of a CME impact associated with the X9 flare which occurred on December 5.

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

Monitoring remarks from a location near N58E06: The most common east coast North American stations (like 930 CJYQ, 1030 WBZ and 1510 WWZN) were noted with mostly poor 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.