Solar Terrestrial Activity Report

Last major update issued on September 18, 2005 at 03:45 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 unsettled on September 17. Solar wind speed ranged between 492 and 642 (all day average 556) km/sec, possibly under the influence of a weak high speed coronal hole stream.

Solar flux measured at 20h UTC on 2.8 GHz was 103.9. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 11.5).
Three hour interval K indices: 22133333 (planetary), 22133333 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was high. A total of 6 C and 1 M class events was recorded during the day. 4 of the C flares were optically uncorrelated.

Region 10808 decayed quickly and lost about half of its penumbral coverage. Although there is still a magnetic delta structure in the main penumbra, the inversion line has shortened considerably. An isolated major flare is still possible. Flares: C2.0 at 02:12, C3.3 at 04:49 and a major impulsive M9.8/2N at 06:05 UTC.
New region 10810 rotated into view at the northeast limb. This region has mixed polarities with both a leading and a trailing positive polarity area. It is not yet clear if there is a magnetic delta structure within the leading asymmetrical penumbra. At least C flares are possible.

Coronal mass ejections (CMEs)

September 16-17: 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

No obvious coronal holes are currently approaching Earth-facing positions.

Processed TRACE mosaic image on September 6, 2005. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 18-20.

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 station tonight: Radio Cristal del Uruguay. Uruguay stations like 930 Radio Monte Carlo and 1590 Radio Real were both received with better than average signals. The only North American stations to be observed, 930 CJYQ and 1130 WBBR, were heard briefly and weakly around 03h UTC.

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.