Solar Terrestrial Activity Report

Last major update issued on September 22, 2004 at 03:00 UTC. Minor update posted 06:07 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update September 2, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 2, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 2, 2004)]
[Historical solar and geomagnetic data charts 1954-2004 (last update August 28, 2004)]
[Archived reports (last update September 11, 2004)]

Recent activity

The geomagnetic field was quiet to unsettled on September 21. Solar wind speed ranged between 373 and 450 km/sec under the influence of a weak and slow coronal hole flow from recurrent coronal hole CH114. The expected CME from the M1 event on September 19 has not arrived.

Solar flux measured at 20h UTC on 2.8 GHz was 94.9. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 10.6).
Three hour interval K indices: 23322222 (planetary), 24322212 (Boulder).

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

At midnight there was 1 spotted region on the visible disk. The solar flare activity level was low. A total of 1 C class event was recorded during the day.

Region 10672 rotated out of view at the northwest limb. Flare: impulsive C7.5 at 08:36 UTC.
Region 10673 decayed slowly and quietly.

Comment added at 06:07 UTC on September 22: A solar wind shock was observed at ACE at about 06h UTC with an increase in solar wind speed from 440 to 540 km/sec. Initially the interplanetary magnetic field has been northwards and it is too early to tell if this disturbance will have significant geomagnetic effects.

Coronal mass ejections (CMEs)

September 19-21: No LASCO observations. A CME was likely associated with the M1.9 event in region 10672 on September 19.

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

No obvious coronal holes are currently approaching geoeffective positions. Recurrent coronal hole CH114 was in a geoeffective position on September 18-19.

Processed SOHO/EIT 284 image at 19:06 UTC on September 10. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on September 22-25. There is still a slight chance of a glancing blow from a CME on September 22. In that case geomagnetic activity could increase to the unsettled to active level.

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 and has improved significantly over the last day. Propagation along long distance north-south paths is poor. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and WLAM Lewiston ME. On other frequencies some stations from Venezuela and Colombia were observed, however, most stations were from the eastern parts of Canada and USA. 1650 kHz had Radio Disney with a fair signal.

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
10672 2004.09.09 1   N04W86 0050 HSX rotated out of view
10673 2004.09.15 12 11 S13W04 0290 DHO classification was DSO
at midnight, area 0250
10674 2004.09.20     S10W36     plage
S453 emerged on
    N21W70     plage
Total spot count: 13 11
SSN: 33 21

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)
2003.07 127.7 83.3 61.8 (-3.2)
2003.08 122.1 72.7 60.1 (-1.7)
2003.09 112.2 48.7 59.6 (-0.5)
2003.10 151.7 65.5 58.2 (-1.4)
2003.11 140.8 67.3 56.8 (-1.4)
2003.12 114.9 46.5 54.8 (-2.0)
2004.01 114.1 37.7 52.0 (-2.8)
2004.02 107.0 45.8 49.3 (-2.7)
2004.03 112.0 49.1 (47.0 predicted, -2.3)
2004.04 101.2 39.3 (44.8 predicted, -2.2)
2004.05 99.8 41.5 (41.5 predicted, -3.3)
2004.06 97.4 43.2 (38.6 predicted, -2.9)
2004.07 119.1 51.0 (36.8 predicted, -1.8)
2004.08 109.6 40.9 (35.4 predicted, -1.4)
2004.09 108.8 (1) 43.1 (2) (34.2 predicted, -1.2)

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]