Solar Terrestrial Activity Report

Last major update issued on September 3, 2005 at 04:30 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 unsettled to minor storm on September 2. Solar wind speed ranged between 431 and 968 (all day average 539) km/sec. A solar wind shock related to the arrival of the halo CME observed on August 31 was observed at 13:42 UTC. Later in the day solar wind speed peaked just below 1000 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 77.1. The planetary A index was 33 (STAR Ap - based on the mean of three hour interval ap indices: 33.4).
Three hour interval K indices: 34544554 (planetary), 24543554 (Boulder).

The background x-ray flux is at the class A3 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 developed slowly early in the day, then decayed again.

Coronal mass ejections (CMEs)

September 1-2: 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.

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 will likely rotate to an Earth facing position on September 1-2. CH185 did not cause any obvious disturbance during the previous rotation. 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 unsettled to major storm on September 3 because of CME effects and quiet to minor storm on September 4. 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 useless. 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 LT28 Rafaela Argentina before 03h UTC, later on only weak signals were noted.

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.