Solar Terrestrial Activity Report

Last major update issued on December 16, 2006 at 06:40 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 unsettled to very severe storm on December 15. Solar wind speed ranged between 548 and 1001 km/s (all day average 701 km/s - decreasing 2 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 87.1. The planetary A index was 104 (STAR Ap - based on the mean of three hour interval ap indices: 103.8). Three hour interval K indices: 88767443 (planetary), 77666333 (Boulder).

The background x-ray flux is at the class A6 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10930 decayed further with the magnetic delta structure in the southern part of the main penumbra weakening. There is still a chance of another major flare.

Coronal mass ejections (CMEs)

December 13: A fast full halo CME was observed shortly after the X3 flare.
December 14: A full halo CME was observed in association with the X1 flare.
December 15: No obvious partly or fully Earth directed CMEs were detected in LASCO imagery.

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 with a trans equatorial extension) will be in an Earth facing position on December 16-17.

Processed SOHO/EIT 195 image at 16:48 UTC on December 15. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active initially on December 16. Sometime during the latter half of the day another CME impact is likely and could cause active to major storm conditions until sometime on December 17. Quiet to unsettled conditions are expected for December 18 while a high speed stream from CH252 could cause unsettled to minor storm conditions on December 19-21.

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: At 03h UTC all audible trans Atlantic stations were from Brazil (740 Sociedade was clearly the strongest signal), Argentina (1030 del Plata was best) and Uruguay. At 05h UTC propagation had changed quite a lot with fairly strong audio from two North American stations: 1470 WLAM and 1510 WWZN.

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.