Solar Terrestrial Activity Report

Last major update issued on September 10, 2004 at 03:40 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 August 25, 2004)]

Recent activity

The geomagnetic field was quiet on September 9. Solar wind speed ranged between 345 and 358 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 131.0. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 5.8).
Three hour interval K indices: 11012122 (planetary), 12122122 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 4 spotted regions on the visible disk. The solar flare activity level was low. A total of 3 C class events was recorded during the day.

Region 10667 decayed very slowly and was quiet.
Region 10669 developed early in the day, then began to decay.
Region 10671 developed quickly during the first half of the day, since then some decay has been observed in the intermediate spots. There is currently a magnetic delta structure in the southern part of the large trailing penumbra. Flare: C2.6 at 06:29 UTC.
New region 10672 rotated into view at the northeast limb. It is not yet clear if the southernmost penumbra should be split into a separate region, magnetograms currently indicate that the two parts of the region are not connected, neither in the positive nor in the negative polarity areas. The southern penumbra has been the most active and the corona above it is hot. C class flaring with associated coronal mass ejections is likely. Flares: long duration C3.2 peaking at 06:01 and C1.0 at 22:16 UTC.

Coronal mass ejections (CMEs)

September 7-9: No obviously Earth directed CMEs were observed. A full halo CME was observed after the C2 event behind the northeast limb on September 7. A CME was observed above the central east limb after the C3 event on September 9.

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 coronal hole (CH113) in the southern hemisphere could rotate into a geoeffective position on September 12.

Processed SOHO/EIT 284 image at 19:06 UTC on September 9. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be mostly quiet on September 10-12.

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 good. Propagation along long distance north-south paths is very poor. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant station tonight: WLAM Lewiston ME. Apart from a few stations from the Caribbean, a large number of North American stations dominated most of the other 10 kHz spaced frequencies in the MW band. WBBR 1130 had an impressive S9+20dB signal with several other stations topping S9. Greenland on 650 kHz had a strong signal as well.

Propagation conditions could improve further during the next few days.

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
10667 2004.09.01 7 8 S11W32 0250 HKX classification was CAO
at midnight, location
10669 2004.09.05 17 16 S06W24 0100 DAO  
10670 2004.09.05     S14W20     this was the trailing
spots of region 10667,
the region should
be deleted
10671 2004.09.06 13 15 S09W68 0300 DAI beta-delta
classification was DAC
at midnight, area 0370
10672 2004.09.09 5 13 N05E73 0300 DAI area was 0160
at midnight
two separate regions?
S451 emerged on
    S06E40     plage
Total spot count: 42 52
SSN: 82 92

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)
2004.09 107.1 (1) 16.4 (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]