Solar Terrestrial Activity Report

Last update December 18, 2002 at 04:20 UTC. Minor update posted at 11:06 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update December 2, 2002)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update December 2, 2002)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update December 2, 2002)]
[Historical solar and geomagnetic data charts 1954-2002 (last update October 13, 2002)]
[Archived reports (last update December 16, 2002)]

Recent activity

The geomagnetic field was quiet to unsettled on December 17. Solar wind speed ranged between 359 and 491 km/sec, gradually decreasing all day. Solar wind density began increasing after 19h UTC in anticipation of the arrival of a strong coronal stream.

Solar flare activity was moderate. Solar flux was 212.5, the planetary A index was 6 (STAR Ap - based on the mean of three hour ap indices: 7.4).
Three hour interval K indices: 22122322 (planetary), 21111212 (Boulder).

The background x-ray flux is at the class C1-C2 level.

At midnight there were 10 spotted regions on the visible disk. A total of 14 C and 1 M class flares were recorded during the day.

Region 10218 decayed and was nearly spotless by late afternoon, then the only remaining spot increased in size again and had gained penumbra by midnight.
Region 10220 was quiet and stable.
Region 10223 remained mostly unchanged and quiet.
Region 10224 developed additional small spots and remains capable of producing a minor M class flare.
Region 10225 decayed significantly and lost about half of its penumbral area.
Region 10226 developed strongly in the leading negative polarity area while slow decay was observed in the trailing spots. The region lost its centrally located magnetic delta structure during the second half of the day. Further M class flaring is likely and there is a chance of a major flare. Flares: C6.0 at 01:00, C1.8 at 02:03, C2.2 at 06:37, C6.4 at 19:30, C6.1 at 23:08 and a long duration M1.6 event peaking at 23:35 UTC.
Region 10227 decayed and lost several of its small spots. The region simplified with no polarity mixing obvious at midnight. Flares: C2.8 at 02:58, C5.3 at 05:06, C4.1 at 08:02 and C5.9/1F at 10:06 UTC.
Region 10228 did not change much and remains unimpressive with only a few tiny spots observed.
Region 10229 decayed losing several trailing spots and some penumbral coverage. An M class flare is possible. Flare: C3.5 at 05:54 UTC.
New region 10230 emerged quickly near the southeast limb.

Comment added at 11:06 UTC on December 18: Region 10226 produced an M2.4 flare at 06:42 UTC. The trailing and intermediate spot sections continue to decay slowly while growth is observed in the leading spot section. Otherwise region 10228 has become spotless. Both regions 10229 and 10227 have been decaying moderately quickly losing spots and penumbral area.

Coronal mass ejections (CMEs)

December 15-17: No obviously geoeffective CMEs noted.

Coronal holes

Coronal hole history (starting late October 2002)
Compare today's report with the situation one solar rotation ago: 28 days ago 27 days ago 25 days ago

A trans equatorial, recurrent extension of the southern polar coronal hole was in a geoeffective position on December 15-16.

Processed SOHO EIT 284 image at 19:06 UTC on December 17. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to major storm on December 18, unsettled to minor storm on December 19 and unsettled to active on December 20 due to a strong coronal stream. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is fair.

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.
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)

Composite image based on a SOHO/MDI continuum image and overlaid by a coronal hole image. Region numbering has been included. Compare to the previous day image.

Data for all numbered solar regions according to the Solar Region Summary provided by SEC/NOAA. 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.

Monthly solar cycle data

1) Running average based on the daily 20:00 UT observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (SEC/NOAA) sunspot number. The official international sunspot number is typically 25-45% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and interpretations, and partly on data from sources noted in solar links. Comments and suggestions are always welcome.