Solar Terrestrial Activity Report

Last major update issued on September 29, 2006 at 03:50 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, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 3, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 3, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update September 8, 2006)]

Recent activity

The geomagnetic field was quiet on September 28. Solar wind speed ranged between 339 and 393 km/s (all day average 362 km/s - decreasing 66 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 73.0. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.5). Three hour interval K indices: 00111001 (planetary), 10112111 (Boulder).

The background x-ray flux is at the class A2 level.

At midnight there were 3 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

New region 10912 rotated into view at the northeast limb.
New region 10913 rotated into view at the southeast limb on September 27 and was numbered the next day by NOAA/SEC.
New region 10914 rotated into view at the southeast limb.

While none of the currently visible regions display significant activity, a much more active region is approaching the east limb. This region may have been the source of the full halo CME observed on September 26 and several smaller CMEs.

Coronal mass ejections (CMEs)

September 26-28: No obvious partly or fully Earth directed CMEs were detected in incomplete LASCO imagery. A full halo CME, probably from a region some days behind the east limb, was observed beginning early on September 26 in LASCO C3 images.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH241) in the southern hemisphere was in an Earth facing position on September 25-27. CH241 has decayed considerably in the northern parts since the previous solar rotation. A small, poorly defined coronal hole in the northern hemisphere, maybe an extension or split from CH241, was in a potentially geoeffective position on September 27.

Processed SOHO/EIT 284 image at 19:06 UTC on September 28. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled, perhaps with isolated active intervals on September 29. Quiet to active conditions is likely on September 30 and October 1 due to a high speed stream from CH241. Mostly quiet conditions are likely on October 2-4.

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) Effects from a CME are likely to be observed at 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. Propagation on long distance northeast-southwest paths is very poor.

A number of east coast North American stations were heard at fair signal levels, a few stations like 1130 WBBR, 1500 WTWP and 1510 WWZN were strong at times. Several stations from Cuba, Venezuela and Colombia enjoyed good reception. No west coast stations were noted this night, while the previous night had stations from that area on 1000 (strong at times), 1090, 1130, 1320, 1410, 1470 (occasionally strong) and 1510 kHz.

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.