Solar Terrestrial Activity Report

Last major update issued on September 12, 2004 at 03:45 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update September 2, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 2, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 2, 2004)]
[Historical solar and geomagnetic data charts 1954-2004 (last update August 28, 2004)]
[Archived reports (last update September 11, 2004)]

Recent activity

The geomagnetic field was quiet to slightly unsettled on September 11. Solar wind speed ranged between 272 and 341 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 116.4. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.4).
Three hour interval K indices: 20013232 (planetary), 00002211 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was high. A total of 1 C and 1 M class events was recorded during the day.

Region 10667 decayed in the main penumbral area. New spots were observed in the south where positive polarity flux emerged. This new development may have been the cause of an impulsive M3.2 flare observed at 01:39 UTC on September 12. A type II radio sweep was associated with this event.
Region 10669 decayed further and lost the trailing spots.
Region 10672 developed in the intermediate spot section. Magnetically this region is a mess with several small patches of negative polarity flux inside the main positive polarity area. There is some positive polarity at the eastern edge of the southern negative polarity penumbra. Further major flares are possible. Flares: C1.1 at 06:34 and a major long duration M5.0 event which began at 23:55 and peaked at 00:57 UTC on September 12. This event was associated with type II and IV radio sweeps and likely a large CME. A filament eruption to the south of the region into the southern hemisphere was observed at the start of the major eruption.

Coronal mass ejections (CMEs)

September 9-11: No obviously Earth directed CMEs were observed.
September 12: A large CME is likely to have been associated with the major event in region 10672. Previous CMEs (when on the backside) from this region have been wide and there's no reason not to assume that this CME was wide as well. In that case the CME could reach Earth sometime between late on September 13 and the afternoon of September 14 (a better estimate is difficult at this time due to inavailability of LASCO images for the most recent hours).

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 coronal hole (CH113) in the southern hemisphere was likely in a marginally geoeffective position on September 11-12.

Processed SOHO/EIT 284 image at 19:06 UTC on September 10. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 12 and most, if not all, of September 13. A CME from the major eruption early on September 12 is likely to reach Earth on September 14 and cause unsettled to major storm conditions. A coronal hole flow from coronal hole CH113 could reach Earth the same day but is not likely to be noticed if the CME arrives first.

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 fair to good. Propagation along long distance north-south paths is very poor. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant station tonight: WLAM Lewiston ME with a good signal (no other stations heard during the night). Stations from the east coast of the USA and the Canadian Atlantic had good to excellent signals, particularly CHER 950, WBBR 1130, WWZN 1510 and WTOP 1500 with signals exceeding the S9 level. WEEI 850, WTIC 1080 and CBG 1400 had significantly better signals than usual too.

After 03h UTC on September 11 propagation swung southwards with stations from Venezuela and Colombia booming in, particularly in the lower half of the MW band.

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% less.

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.