Solar Terrestrial Activity Report

Last major update issued on December 25, 2004 at 05:10 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 inactive to quiet on December 24. Solar wind speed ranged between 351 and 416 km/sec. A coronal hole flow reached Earth early on December 25 and is currently causing unsettled to active conditions.

Solar flux measured at 20h UTC on 2.8 GHz was 97.2. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.8).
Three hour interval K indices: 00011211 (planetary), 10021221 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was low. A total of 1 C class events were recorded during the day. That event was a long duration C1.8 event which occurred in a large negative polarity area in the southeast quadrant. Peak emissions were at 03:56 UTC. A slow moving CME was observed over the southeast limb in LASCO images at 06h UTC and may have been associated with this event. Another event worthy of mention was a slow filament eruption in the northwest quadrant. This was a large filament disappearing starting at approximately 05h UTC and was associated with a CME off of the northwest limb.

Region 10713 decayed slowly and quietly.

Coronal mass ejections (CMEs)

December 24: A partial halo CME covering the entire east limb and the south pole was observed in LASCO C3 images after 16h UTC. With a data gap in LASCO images after the CMEs observed in the morning and this CME, it is difficult to state if this CME was actually a continuation of the CME then observed off of the southeast limb or a separate event. If it was a separate event (the most likely possibility), its source would have been behind the southeast limb.
December 23: Only a few images available, no obviously Earth directed CMEs observed.
December 22: No images available.

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 (CH135) in the northern hemisphere was in a geoeffective position on December 23-24.

Processed SOHO/EIT 284 image at 18:03 UTC on December 11. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be unsettled to active on December 25-27 with a possibility of isolated minor storm intervals due to a high speed stream from coronal hole CH135. Quiet to unsettled is likely on December 28-29.

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 fair. Propagation along long distance north-south paths is poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: WLAM Lewiston ME with a weak signal. Propagation was best on lower frequencies with i.e. CBNA on 600 and CHLC on 610 kHz having nice signals.

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
10712 2004.12.17     S11W41     plage
10713 2004.12.17 20 14 S08W21 0190 EAI classification was DAO
at midnight
10714 2004.12.22 2   S03W30 0020 CRO spotless
Total spot count: 22 14
SSN: 42 24

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 93.6 (1) 28.5 (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]