Solar Terrestrial Activity Report

Last major update issued on September 17, 2005 at 03:40 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 16. Solar wind speed ranged between 537 and 729 (all day average 618) km/sec.

Solar flux measured at 17h UTC on 2.8 GHz was 111.8 (the measurement at 20h UTC was flare enhanced). The planetary A index was 18 (STAR Ap - based on the mean of three hour interval ap indices: 18.0).
Three hour interval K indices: 44343232 (planetary), 44343122 (Boulder).

The background x-ray flux is at the class B6 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was moderate. A total of 6 C and 4 M class events was recorded during the day.

Region 10808 decayed further and lost some area in the northeastern part of the main penumbra. This penumbra still has a strong magnetic delta structure with only minor separation between opposite polarity umbrae. Flares: M4.4/1B at 01:49, M2.1 at 02:14, C1.1 at 05:23, C1.2 at 08:58, C1.5 at 13:13, C6.1 at 14:45, C7.9 at 15:15, M1.3 at 17:48, M3.5/1F at 19:36 and C6.2 at 23:39 UTC.

Coronal mass ejections (CMEs)

September 15: There may have one or two smaller Earth directed CMEs associated with M and X class flares. LASCO data for the day is incomplete.
September 16: 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

Coronal holes cannot currently be reliably observed as the relevant GOES SXI, TRACE and SOHO data are all unavailable.

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 active on September 17-19.

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. Not that many other stations were heard during the night, interestingly 980 Rádio Nacional (Brazil) had a huge signal at 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.