Solar Terrestrial Activity Report

Last major update issued on December 31, 2004 at 03:20 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update December 3, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update December 3, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update December 3, 2004)]
[Historical solar and geomagnetic data charts 1954-2004 (last update November 8, 2004)]
[Archived reports (last update December 24, 2004)]

Recent activity

The geomagnetic field was quiet to active on December 30. Solar wind speed ranged between 406 and 588 km/sec. A new disturbance arrived at approximately 04h UTC. While the source of this disturbance is unknown, ACE and SOHO solar wind data indicate that the origin was not a coronal hole.

Solar flux measured at 20h UTC on 2.8 GHz was 100.0. The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 14.9).
Three hour interval K indices: 23433423 (planetary), 34344332 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 6 C and 2 M class events were recorded during the day.

Region 10715 developed more spots, however, some decay was observed in the central parts of the region, probably due to flare effects. The region is compact and complex with one magnetic delta structure in the central part and another one in the southwest. Further M class flares are likely. Flares: C2.5 at 06:24, C1.6 at 07:42, C1.3 at 10:17, M2.2 (with an associated weak type II radio sweep) at 10:47, C2.6 at 12:17, C1.0 at 13:19, C4.1 at 21:52 and M4.2/2N (with an associated weak type II radio sweep) at 22:18 UTC.
New region 10716 emerged in the southeast quadrant early in the day, slow decay was observed during the latter half of the day.

Coronal mass ejections (CMEs)

December 30: A full halo CME was observed after the M2.2 event in region 10715 before noon. The CME was faint over the poles and the west limbs. Another and faster CME was likely launched after the M4 event in region 10715 late in the day. This CME could reach Earth on January 1 or 2.
December 29
: The CME associated with the M2.3 flare in region 10715 was well defined over the east limb, very faint extensions were observed around the remainder of the disk.
December 28:
No obviously 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 poorly defined extension (CH137) of a coronal hole in the northern hemisphere was in a geoeffective position on December 29. Recurrent trans equatorial coronal hole CH136 will rotate into a geoeffective position on December 31-January 1.

Processed SOHO/EIT 284 image at 12:57 UTC on December 30. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on December 30 - January 2.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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.


Long distance low and medium 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 normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración and WLAM Lewiston, both with fairly weak signals. Only a few signals were noted on other frequencies, most of them from the easternmost parts of the USA. 

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.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10715 2004.12.28 12 18 N04E47 0350 DKC beta-delta
10716 2004.12.30 2 1 S16E52 0010 BXO classification was AXX
at midnight
S491 emerged on
    S16W37     plage
Total spot count: 14 19
SSN: 34 39

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2003.10 151.7 65.5 58.2 (-1.3)
2003.11 140.8 67.3 56.7 (-1.5)
2003.12 114.9 46.5 54.8 (-1.9)
2004.01 114.1 37.3 52.0 (-2.8)
2004.02 107.0 45.8 49.3 (-2.7)
2004.03 112.0 49.1 47.1 (-2.2)
2004.04 101.2 39.3 45.5 (-1.6)
2004.05 99.8 41.5 43.9 (-1.6)
2004.06 97.4 43.2 (42.2 predicted, -1.7)
2004.07 119.1 51.0 (40.6 predicted, -1.6)
2004.08 109.6 40.9 (39.0 predicted, -1.6)
2004.09 103.1 27.7 (37.1 predicted, -1.9)
2004.10 105.9 48.4 (34.9 predicted, -2.2)
2004.11 113.2 43.7 (33.0 predicted, -1.9)
2004.12 94.4 (1) 33.0 (2) (30.7 predicted, -2.3)

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 some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.

[DX-Listeners' Club]