Solar Terrestrial Activity Report

Last major update issued on September 4, 2005 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, 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 2 , 2005)]

Recent activity

The geomagnetic field was quiet to major storm on September 3. Solar wind speed ranged between 549 and 783 (all day average 601) km/sec under the influence of CME effects during the first half of the day, then under the influence of a high speed stream from CH185.

Solar flux measured at 20h UTC on 2.8 GHz was 74.2. The planetary A index was 32 (STAR Ap - based on the mean of three hour interval ap indices: 31.9).
Three hour interval K indices: 66453324 (planetary), 65453212 (Boulder).

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

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10805 decayed slowly and quietly.

Coronal mass ejections (CMEs)

September 1-3: Another large CME from a backsided source was observed just before midnight on September 1 in LASCO images. At the same time there appears to have been a second CME, probably related to a long duration B4 event in region 10803. This CME could reach Earth on September 4 and cause unsettled to minor storm conditions. At 03:42 UTC on September 3 another large, full halo CME was observed in LASCO images. The source is about 3-4 days behind the southeast limb. This backsided region has produced several large CMEs over the last week.

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 small recurrent coronal hole (CH185) in the northern hemisphere was in an Earth facing position on September 1-2. A poorly defined recurrent coronal hole (CH186) in the northern hemisphere will likely be in an Earth facing position on September 4-5.

Processed SOHO/EIT 284 image at 13:06 UTC on September 2. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on September 4 due to a high speed stream and a possible CME impact. Quiet to active is likely on September 5-6.

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 to poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Vibración (Venezuela), both with fairly strong signals. Uruguay was noted on 930, 1510 and 1590 kHz as well. After LSR on September 3 there was an unusually good opening to Brazil on frequencies above 1400 kHz, for instance two stations on 1560 kHz had good signals for quite some time.

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.