Solar Terrestrial Activity Report

Last major update issued on September 20, 2005 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 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 on September 19. Solar wind speed ranged between 381 and 558 (all day average 445) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 91.1. The planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 7.5).
Three hour interval K indices: 22222221 (planetary), 21333331 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was low. A total of 2 C class events was recorded during the day, all optically uncorrelated.

Region 10808 decayed losing all spots outside of the main penumbra. The region is rotating over the southwest limb.
Region 10810 decayed slowly. C class flares are possible.

Coronal mass ejections (CMEs)

September 17-19: 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 20-22.

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 poor. 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 Cristal del Uruguay and Radio Vibración (Venezuela). A few North American stations were noted with a fair signal from 930 CJYQ and weak signals from a number of other Newfoundland stations. WWZN 1510 was weak as well. Trinity Broadcasting on 820 kHz was fair to good.

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.