Solar Terrestrial Activity Report

Last major update issued on September 13, 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 September 11, 2004)]

Recent activity

The geomagnetic field was quiet on September 12. Solar wind speed ranged between 277 and 335 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 114.6. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 5.1).
Three hour interval K indices: 11002222 (planetary), 21011211 (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 moderate. A total of 2 C and 1 M class events was recorded during the day.

Region 10667 decayed slowly and will soon rotate out of view at the southwest limb. Flares: M3.2 at 01:39 (with an associated moderate type II radio sweep) and C1.1 at 22.27 UTC.
Region 10669 decayed slowly and quietly and will soon rotate over the southwest limb.
Region 10672 developed further with many new small spots emerging in the central part of the region. Magnetically the region is slightly less complex than yesterday with the negative polarity area in the northwest becoming somewhat better separated from the trailing positive polarity area. M class flares are possible. Flares: C2.0 at 18:34 UTC.

Coronal mass ejections (CMEs)

September 10-11: No obviously Earth directed CMEs were observed.
September 12: A large full halo CME was associated with the M4.8 long duration event which began at 23:55 UTC on September 11 and peaked nearly one hour later. Although most of ejected material was observed over the east limbs, Earth will receive an impact from at least the outer leading edge of this CME and perhaps even from a part of the core CME. The impact time will likely be near noon on September 14.

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 was likely in a marginally geoeffective position on September 11-12.

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 on September 13 and early on September 14. A CME impact on September 14 will likely cause unsettled to major storm conditions that day and early on September 15. A coronal hole flow from coronal hole CH113 could reach Earth on September 14 but is not likely to be noticed if the CME arrives first.

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 to occasionally excellent. 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 early on, later several stations from the USA were noted. Propagation on other frequencies was best towards the eastern and central parts of the USA with lots of interesting stations heard throughout the MW band.

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 4 3 S11W72 0230 CAO area was 0160
at midnight
10669 2004.09.05 2 2 S06W66 0080 HSX area was 0060
at midnight
10672 2004.09.09 49 41 N05E33 0260 EAI beta-gamma
S451 emerged on
    S06E01     plage
Total spot count: 55 46
SSN: 85 76

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)
2004.09 110.4 (1) 25.1 (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]