Solar Terrestrial Activity Report

Last major update issued on September 16, 2004 at 02:30 UTC. The next update will be on September 20 as I will be away for a few days.

[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 active on September 15. Solar wind speed ranged between 542 and 677 km/sec, first under the lingering effects of the CME observed on September 13-14, then under the influence of a high speed stream from coronal hole CH113.

Solar flux measured at 20h UTC on 2.8 GHz was 109.6. The planetary A index was 14 (STAR Ap - based on the mean of three hour interval ap indices: 15.3).
Three hour interval K indices: 43233332 (planetary), 43122312 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was low. A total of 4 C class events was recorded during the day. A C1.3 long duration event peaking at 20:55 UTC had its origin behind the southwest limb.

Region 10672 developed new spots to the immediate north and northeast of the leading penumbrae early in the day. Then the region began to decay and lost penumbra and spots, particularly in the trailing spot section. M class flares are possible. Flares: C2.7 at 07:49, C1.1 at 17:13, C1.1 at 17:51 UTC.
New region 10673 rotated fully into view at the southeast limb. The region doesn't appear to be complex spotwise, however, magnetograms hint at some complexity and the region is probably capable of C class flaring.

Spotted regions not numbered by NOAA/SEC:
[S453] This unipolar region emerged on September 15 in the northeast quadrant with a single, small spot.

Coronal mass ejections (CMEs)

September 13-15: No obviously Earth directed CMEs were 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

No obvious coronal holes are currently approaching geoeffective positions.

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 active on September 16 and quiet to unsettled on September 17-18.

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 monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). On other frequencies Puerto Rico was noted on 580, 1600 and 1660 kHz while the most usual stations from Newfoundland and Nova Scotia had fair signals as early as 23:30 UTC. 

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 46 44 N05W03 0320 EAI beta-gamma
10673 2004.09.15 1 4 S13E72 0140 HAX formerly region S452
classification was CSO
at midnight
S451 emerged on
    S06W38     plage
S453 emerged on
  1 N21E08 0000 AXX  
Total spot count: 47 49
SSN: 67 79

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)
2004.09 111.1 (1) 31.8 (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]