Solar Terrestrial Activity Report

Last major update issued on September 26, 2005 at 04:20 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 inactive to unsettled on September 25. Solar wind speed ranged between 285 and 399 (all day average 334) km/sec. An unexpected disturbance began at about 10h UTC. This disturbance has an unknown source and has been observed with unusual changes in solar wind speed, density and temperature.

Solar flux measured at 20h UTC on 2.8 GHz was 81.0. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.9).
Three hour interval K indices: 10023202 (planetary), 11122112 (Boulder).

The background x-ray flux is at the class A2 level.

At midnight there were 3 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 was quiet and stable.
Region 10812 lost the small trailing spot.

Spotted regions not numbered by NOAA/SEC:
[S594] This region emerged in the southwest quadrant on September 25. Location at midnight: S15W66.

A thick and large filament is currently in the northern hemisphere across the central meridian. At its eastern termination there is another filament shaped as a question mark. If this configuration becomes unstable over the next few days we could get a large Earth directed CME.

Coronal mass ejections (CMEs)

September 23-25: 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 coronal hole (CH188) in the southern hemisphere may have been in an Earth facing position on September 24, however, there is a chance CH188 may have been too far to the south to become geoeffective. A recurrent trans equatorial coronal hole (CH189) will rotate to an Earth facing position on September 26-27.

Processed SOHO/EIT 284 image at 01:06 UTC on September 26. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on September 26, quiet to unsettled on September 27-28 and become unsettled to active on September 29-30 due to a high speed stream from CH189.

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 poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: At 02 UTC Rádio Rural AM de Parelhas (Brazil) was the only station on the frequency, later on Radio Cristal del Uruguay took over dominance. A weak signal from 1510 WWZN was the only trace remaining of the good propagation conditions to North America observed the previous day.

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 5 1 N08W35 0150 CAO classification was HAX at midnight
10811 2005.09.19     S10W78     plage
10812 2005.09.23 3 3 S02E45 0020 CSO classification was HAX at midnight
S594 2005.09.25   1 S16W66 0010 AXX  
Total spot count: 8 5  
SSN: 28 35  

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 94.2 (1) 35.7 (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]