Solar Terrestrial Activity Report

Last major update issued on September 28, 2007 at 03:55 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 major storm on September 27. Solar wind speed ranged between 351 and 534 km/s (average speed was 412 km/s, decreasing 26 km/s from the previous day). A sudden change in solar wind density and speed was observed at 10:52 UTC at SOHO. This was associated with the arrival of a high speed stream from CH292. Between 14h and 15h30 UTC the interplanetary magnetic field was strongly southwards at ACE, this later led to an isolated major storm interval.

Solar flux measured at 20h UTC on 2.8 GHz was 67.1. The planetary A index was 19 (STAR Ap - based on the mean of three hour interval ap indices: 18.8). Three hour interval K indices: 00021654 (planetary), 00022543 (Boulder).

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

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Spotted regions not numbered by NOAA/SEC:
[S708] This region emerged in the northeast quadrant on September 27. Location at midnight: N03E19

Coronal mass ejections (CMEs)

September 25-27: 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 (CH292) in the southern hemisphere was an Earth facing position on September 24-25. Another recurrent coronal hole (CH293) in the southern hemisphere will be in an Earth facing position on September 28.

Processed SOHO/EIT 195 image at 00:00 UTC on September 28. 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. Propagation on long distance northeast-southwest paths is fair.

Monitoring remarks from a location near N58E06: September 26-27: At 22h UTC all the usual Newfoundland and Nova Scotia stations were audible at good levels. A few minutes later stations from the northeastern USA (like 1390 WEGP and 1470 WLAM) became audible and at 23h UTC most of the New York 50 kW stations had strong signals. On 1470 kHz WWNN had become the dominant signal. Stations from Puerto Rico and Venezuela and a few from Brazil were heard well too.


The geomagnetic field is expected to be quiet to minor storm on September 28. Quiet to unsettled conditions are likely on September 29-30. October 1 could see a few unsettled and active intervals due to effects from CH293. Generally quiet conditions are expected for October 2-16.

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
S708 2007.09.27   4 N03E19 0030 CSO  
Total spot count: 0 4  
SSN: 0 14  

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 67.1 (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]