Solar Terrestrial Activity Report

Last major update issued on September 15, 2007 at 03:00 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update July 23, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 23, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 23, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update July 1, 2007)]

Recent activity

The geomagnetic field was quiet to unsettled on September 14. Solar wind speed ranged between 277 and 370 km/s (average speed was 299 km/s, increasing 23 km/s over the previous day). A low speed stream from CH290 arrived at about 16h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 66.8. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.0). Three hour interval K indices: 10000232 (planetary), 10012322 (Boulder).

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

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

September 12-14: No obvious fully or partly Earth directed CMEs were observed in LASCO imagery.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH290) in the southern hemisphere was in an Earth facing position on September 10-11. A recurrent trans equatorial coronal hole (CH291) will likely rotate into an Earth facing position on September 17-21.

Processed STEREO 195 image at 21:05 UTC on September 14. The darkest areas on the solar disk are likely coronal holes.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is fair to good. Propagation on long distance northeast-southwest paths is poor to fair.

Monitoring remarks from a location near N58E06: September 15: Propagation was best to northeast USA and eastern Canada. 1250 CJYE was excellent and lots of stations were noted on all GY frequencies. 590 had both VOCM and WEZE. Some stations from Venezuela and Cuba had good signals in the low half of the AM band near LSR.


The geomagnetic field is expected to be quiet to unsettled on September 15, possibly with an isolated active interval due to effects from CH290. Quiet conditions are likely on September 16-20. A high speed stream from CH291 could cause quiet to active conditions on September 21-24.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)

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) Effects from a CME are likely to be observed at 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.

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
Total spot count: 0 0  
SSN: 0 0  

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)
2006.07 75.7 12.2 15.3 (-1.0)
2006.08 79.0 12.9 15.6 (+0.3)
2006.09 77.8 14.4 15.6 (+0.0)
2006.10 74.3 10.4 14.2 (-1.4)
2006.11 86.3 21.5 12.7 (-1.5)
2006.12 84.5 13.6 12.1 (-0.6)
2007.01 83.3 16.9 12.0 (-0.1)
2007.02 77.7 10.6 11.6 (-0.4)
2007.03 72.2 4.8 (11.1 predicted, -0.5)
2007.04 72.4 3.7 (10.7 predicted, -0.4)
2007.05 74.4 11.7 (10.2 predicted, -0.5)
2007.06 73.7 12.0 (10.0 predicted, -0.2)
2007.07 71.6 10.0 (10.0 predicted, +0.0)
2007.08 69.1 6.2 (10.3 predicted, +0.3)
2007.09 67.4 (1) 3.2 (2) (11.5 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% 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]