Solar Terrestrial Activity Report

Last major update issued on December 23, 2003 at 04:45 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 22. Solar wind speed ranged between 548 and 682 km/sec under the influence of a high speed stream from coronal hole CH72. Solar wind data after 02h UTC on December 23 indicate that the high speed stream is ending.

Solar flux measured at 20h UTC on 2.8 GHz was 137.6. The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 15.5).
Three hour interval K indices: 33343332 (planetary), 43333433 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight there were 6 spotted regions on the visible disk. Solar flare activity was low. A total of 9 C class events were recorded during the day.

Region 10520 rotated quietly to the northwest limb.
Region 10523 was quiet and stable.
Region 10525 decayed in the leading and trailing spot sections. There is still a weak magnetic delta structure in a central penumbra. A minor M class flare is possible.
Region 10528 decayed in the central spot section while quick development was observed in the trailing spot section. The region may soon have to be split into two as there are two separate bipolar spot sets. A weak magnetic delta structure has developed in a trailing. A minor M class flare is likely and the possibility of a major event is increasing. Flares: C5.5 at 00:45, C1.7 at 11:09, C2.3 at 13:56, C1.6 at 14:41, C1.2 at 15:45, C3.7 at 19:50 and C1.8 at 21:39 UTC.
Region 10530 developed slowly. While the region is not currently complex, the spots are located in a fairly large area with bright plage. Flares: C2.2 at 06:54 and C1.6 at 20:41 UTC.
New region 10531 was first observed on December 20 and was numbered by SEC two days later. The region is becoming interesting with both negative and positive magnetic flux emerging. The inversion line is mostly east-west.

Coronal mass ejections (CMEs)

December 20-22: 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 07:06 UTC on December 22. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled December 23-27.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation along long distance north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay at first, then Radio Vibración (Venezuela), both with fairly weak signals . Again WWZN Boston on 1510 kHz was heard with a fair signal, as were a few other station from the US east coast].

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.