Solar Terrestrial Activity Report

Last major update issued on September 29, 2005 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 3, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 3, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 3, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update September 14, 2005)]

Recent activity

The geomagnetic field was quiet to active on September 28. Solar wind speed ranged between 334 and 396 (all day average 358) km/sec. Solar wind density is still significantly above average.

Solar flux measured at 20h UTC on 2.8 GHz was 74.6. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 12.1).
Three hour interval K indices: 33422323 (planetary), 44421322 (Boulder).

The background x-ray flux is at the class A1 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day. 

Region 10810 decayed slowly and quietly.
Region 10812 decayed slowly and quietly.

Coronal mass ejections (CMEs)

September 26-28: No obvious fully or partly 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

A recurrent trans equatorial coronal hole (CH189) was in an Earth facing position on September 26-27. The brief appearance on September 26 of a spotted region in the western part of CH189 caused a reduction in the size of the coronal hole. A small recurrent coronal hole (CH190) in the northern hemisphere could rotate to an Earth facing position on October 2.

Processed SOHO/EIT 284 image at 19:18 UTC on September 28. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on September 29-30 due to a high speed stream from CH189. Quiet conditions are likely on October 1-4 becoming quiet to unsettled, perhaps with occasional active intervals, on October 5-6 due to effects from CH190. 

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 very poor. Propagation on long distance northeast-southwest paths is good. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Vibración, both with occasionally strong signals. Lots of stations from Venezuela and Colombia were noted on other frequencies, e.g. 1070 kHz which had both Radio Mundial Zulia (Venezuela) and Radio Santa Fe (Colombia) with fair signals. Argentine stations were present as well with good signals from 1030 Radio del Plata and 1510 Radio Belgrano. Some stations from the Caribbean had nice signals as well with 1400 Harbour Light and 1620 WDHP best.

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
10810 2005.09.17 1 1 N08W74 0180 HAX  
10812 2005.09.23 1 1 S02E05 0020 HAX  
Total spot count: 2 2  
SSN: 22 22  

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)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 35.9 (-1.6)
2004.11 113.2 43.5 35.3 (-0.6)
2004.12 94.5 17.9 35.2 (-0.1)
2005.01 102.2 31.3 34.6 (-0.6)
2005.02 97.2 29.2 33.9 (-0.7)
2005.03 89.9 24.5 (33.5 predicted, -0.4)
2005.04 86.0 24.4 (32.2 predicted, -1.3)
2005.05 99.3 42.6 (29.9 predicted, -2.3)
2005.06 93.7 39.6 (28.7 predicted, -1.2)
2005.07 96.4 39.9 (27.7 predicted, -1.0)
2005.08 90.5 36.4 (25.8 predicted, -1.9)
2005.09 92.4 (1) 38.0 (2) (24.2 predicted, -1.6)

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% lower.

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]