Solar Terrestrial Activity Report

Last major update issued on September 28, 2005 at 03:25 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 quiet to active on September 27. Solar wind speed ranged between 345 and 394 (all day average 363) km/sec. Solar wind density is still significantly above average.

Solar flux measured at 20h UTC on 2.8 GHz was 76.9. The planetary A index was 13 (STAR Ap - based on the mean of three hour interval ap indices: 12.8).
Three hour interval K indices: 34232213 (planetary), 34332213 (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 25-27: 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 was too far to the south to become geoeffective. Anyway CH188 has lost a significant portion of its area over the last rotation. A recurrent trans equatorial coronal hole (CH189) was in an Earth facing position on September 26-27. The brief appearance on September 26 of a spotted region in the western part of CH189 caused a reduction in the size of the coronal hole.

Processed SOHO/EIT 284 image at 13:06 UTC on September 27. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on September 28 and become unsettled to minor storm on September 29-30 due to a high speed stream from CH189. Quiet to unsettled is likely on October 1-3.

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 very poor. Propagation on long distance northeast-southwest paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and LT28 Rafaela Argentina. On other frequencies propagation was best towards Uruguay (930 Radio Monte Carlo, 1590 Radio Real) and Argentina (700 Radio Cordoba, 1510 Radio Belgrano). From Puerto Rico both 1480 WMDD and 1660 WGIT had weak to fair signals.

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.