Solar Terrestrial Activity Report

Last major update issued on December 21, 2003 at 05:00 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 active on December 20. Solar wind speed ranged between 304 and 490 km/sec, generally increasing all day under the influence of a high speed stream from coronal hole CH72.

Solar flux measured at 20h UTC on 2.8 GHz was 130.1. The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 17.4).
Three hour interval K indices: 12243444 (planetary), 11243533 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight there were 7 spotted regions on the visible disk. Solar flare activity was low. A total of 4 C class events were recorded during the day.

Region 10520 decayed slowly and quietly.
Region 10523 decayed and could soon become spotless.
Region 10524 decayed and had only a single small spot left at the end of the day. The region will probably become spotless today.
Region 10525 decayed and lost penumbral area in all parts of the region with the exception of the main trailing penumbra. That penumbra contains a magnetic delta structure. A minor M class flare is possible. Flares: C2.6 at 00:16 and C1.5 at 01:58 UTC.
Region 10528 developed slowly and could produce a minor M class flare. A weak magnetic delta structure has developed in the trailing spot section. Flares: C1.8 at 02:22 and C1.8 at 14:31 UTC.

Spotted regions not numbered by NOAA/SEC:
[S327] This region rotated into view at the southeast limb on December 20. Location at midnight: S20E72.
[S328] A new region emerged slowly in the northeast quadrant near the center of the visible disk on December 20. Location at midnight: N04E05.

Coronal mass ejections (CMEs)

December 18-20: 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 was in a geoeffective position on December 17-20.

Processed SOHO/EIT 284 image at 19:06 UTC on December 20. 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 21-22 and quiet to active on December 23 under the influence of a high speed stream from coronal hole CH72. Quiet to unsettled is likely on December 24-26.

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). A few stations from Brazil were heard as well].

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.