Solar Terrestrial Activity Report

Last major update issued on September 25, 2005 at 04:00 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 quiet on September 24. Solar wind speed ranged between 289 and 353 (all day average 303) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 81.4. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.6).
Three hour interval K indices: 11101111 (planetary), 11111110 (Boulder).

The background x-ray flux is at the class A2 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 was quiet and stable.

Coronal mass ejections (CMEs)

September 22-24: 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 25. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be mostly quiet on September 25-28 with a chance of unsettled or active intervals on September 27-28 if a high speed stream from CH188 arrives.

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) 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.

Propagation

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. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and WLAM Lewsiton ME. Although there were a few Spanish language stations around, mainly from Cuba and Venezuela, most of the stations heard were from the easternmost parts of the USA (examples: 1430 WENE and 1480 WSAR) and Canada. Some stations further inland were audible as well with 1120 KMOX St.Louis MO a good indication of above average conditions.

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.

Monthly solar cycle data

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.