Solar Terrestrial Activity Report

Last major update issued on September 2, 2007 at 04:50 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 1. Solar wind speed ranged between 388 and 521 km/s (average speed was 453 km/s, increasing 79 km/s over the previous day) under the influennce of a high speed stream from CH288.

Solar flux measured at 20h UTC on 2.8 GHz was 70.8. The planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 10.8). Three hour interval K indices: 22332223 (planetary), 23243323 (Boulder).

The background x-ray flux is below 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 10969 decayed quickly and could become spotless before rotating out of view at the southwest limb.
New region 10970 emerged in the southeast quadrant early on August 31 and was numbered the next day by NOAA/SEC. The region developed on September and could produce occasional C flares.

Coronal mass ejections (CMEs)

August 30 - September 1: No obvious fully or partly Earth directed CMEs were observed in incomplete 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 (CH288) in the southern hemisphere was in an Earth facing position on August 28-29. A recurrent coronal hole (CH289) in the southern hemisphere will be in an Earth facing position on September 2.

Processed SOHO/EIT 195 image at 19:48 UTC on August 31. 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 poor to very poor. Propagation on long distance northeast-southwest paths is fair.

Monitoring remarks from a location near N58E06: August 31 - September 1: Relatively strong signals were noted from many TA stations from Newfoundland in the north to Argentina in the south. 1350 Radio Buenos Aires was excellent at 23:15 UTC while at the same time 1400 CBG was strong. Later on lots of signals from the USA (east coast), the Caribbean and northern South America were audible at fair to good levels.


The geomagnetic field is expected to be quiet to minor storm on September 2  and quiet to unsettled on September 3 due to effects from CH288. Mostly quiet conditions are likely on September 4-5 while a high speed stream from CH289 could cause a few unsettled and active intervals on September 6.

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
10969 2007.08.21 1 1 S06W72 0030 HRX classification was AXX, area 0010 at midnight
10970 2007.09.01 5 6 S06W07 0050 CAO formerly region S707
classification was DAO at midnight
Total spot count: 6 7  
SSN: 26 27  

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 70.8 (1) 0.9 (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]