Solar Terrestrial Activity Report

Last major update issued on December 19, 2003 at 05:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update December 2, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update December 2, 2003)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update December 2, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update October 15, 2003)]
[Archived reports (last update December 17, 2003)]

Recent activity

The geomagnetic field was quiet to unsettled on December 18. Solar wind speed ranged between 336 and 423 km/sec, gradually decreasing all day.

Solar flux measured at 20h UTC on 2.8 GHz was 123.0. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.4).
Three hour interval K indices: 13233321 (planetary), 13112221 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 7 spotted regions on the visible disk. Solar flare activity was low. A total of 18 C class events were recorded during the day.

Region 10520 was quiet and stable.
Region 10521 was quiet and stable.
Region 10523 added a spot to the northeast of the main penumbra.
Region 10524 was mostly unchanged and quiet.
Region 10525 developed in the trailing spot section where the magnetic delta structure in the largest penumbra strengthened. Another delta could be forming further south. The chance of a minor M class flare is increasing. Flares: C2.1 at 01:51, C1.3 at 04:18, C3.4 at 08:43 (this flare coincided with a flare at the southwest limb, hard to tell which of the sources contributed most to this event), C8.6 at 09:31, C2.9 at 12:37, C1.0 at 13:51, C1.4 at 14:29 (although there was a flare in this region at this time, the flare that contributed the most was probably an event in a region at the southwest limb), C1.9 at 20:24, C3.5 at 22:16, C1.7 at 22:27 and C1.3 at 23:46 UTC.
Region 10527 was quiet and stable.
New region 10528 rotated partly into view at the northeast limb on December 17 and was numbered by SEC the next day. There is a magnetic delta structure in the eastern part of the leading penumbra and possibly another delta in the largest trailing penumbra. A minor M class flare is possible. Flares: C1.1 at 00:32, C1.1 at 01:03, C1.3 at 01:12, C1.2 at 01:19, C1.4 at 11:47, C5.5 at 12:09 (this event was preceded by a few minutes by another, smaller flare in region 10525) and C1.4 at 18:40 UTC.

Coronal mass ejections (CMEs)

December 16-18: No partly or fully earth directed CMEs 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 in the northern hemisphere (CH72) with a trans equatorial extension will rotate into a geoeffective position on December 17-19.

Processed SOHO/EIT 284 image at 19:06 UTC on December 18. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled during the first half of Dec.19. Sometime during the latter half of Dec.19 a high speed stream from coronal hole CH72 will arrive and could cause unsettled to minor storm conditions until December 22.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor. Propagation along long distance north-south paths is fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Rafaela (Argentina). No trace of WDHP on 1620 kHz when I listened tonight].

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.

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% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from sources noted in solar links. All time references are to the UTC day. Comments and suggestions are always welcome.