Solar Terrestrial Activity Report

Last major update issued on December 18, 2003 at 03:50 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 17. Solar wind speed ranged between 407 and 497 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 117.5. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 11.0).
Three hour interval K indices: 23333331 (planetary), 24312321 (Boulder).

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

At midnight there were 8 spotted regions on the visible disk. Solar flare activity was low.

Region 10520 decayed further and lost most of the small spots observed one day earlier.
Region 10521 decayed and could soon become spotless.
Region 10523 was quiet and stable.
Region 10524 developed slowly and quietly.
Region 10525 developed fairly quickly with a weak magnetic delta structure forming in the northernmost penumbra. A minor M class flare is possible. Flare: C8.6 at 03:13 UTC.
New region 10526 emerged in the northwest quadrant on December 16 and was numbered the next day by SEC. The region developed slowly on Dec.17.
New region 10527 was spotted as early as on Dec.13, then decayed. New spots emerged on Dec.16 and the region was numbered the next day by SEC. The region decayed significantly on Dec.17 and could soon become spotless again.

Spotted regions not numbered by NOAA/SEC:
[S325] A new region is rotating into view at the northeast limb. Location at midnight: N08E82. This region was fairly active all day on Dec.17 and may be capable of producing a minor M class flare. Flares: C1.8 at 06:23, C1.0 at 12:06, C1.0 at 13:09 and C1.3 at 20:17 UTC.

Coronal mass ejections (CMEs)

December 15-17: 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 17. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on December 18 and the first half of Dec.19. From the latter half of Dec.19 until Dec.22 a high speed stream from coronal hole CH72 will dominate the solar wind and cause unsettled to minor storm conditions.

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 fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Vibración (Venezuela)].

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.