Solar Terrestrial Activity Report

Last major update issued on December 24, 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 December 18, 2006)]

Recent activity

The geomagnetic field was quiet to active on December 23. Solar wind speed ranged between 547 and 707 km/s (all day average 581 km/s - decreasing 81 km/s from the previous day) under the influence of a high speed stream from CH252.

Solar flux measured at 20h UTC on 2.8 GHz was 72.7. The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 14.6). Three hour interval K indices: 22323442 (planetary), 23333442 (Boulder).

The background x-ray flux is far below the class A1 level.

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

December 21-23: 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

A small coronal hole (CH253) in the southern hemisphere could rotate into an Earth facing position on December 24. CH253 decayed on December and could close completely before rotating into a potential geoeffective position.

Processed SOHO/EIT 195 image at 00:00 UTC on December 24. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on December 24 due to effects from CH252, occasional active intervals are possible. Quiet conditions are likely on December 25-28 with a small chance of unsettled intervals on December 27 due to effects from CH253.

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: At 05h UTC no audio was heard from any trans Atlantic stations.

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.