Solar Terrestrial Activity Report

Last major update issued on September 7, 2005 at 03:20 UTC. Super flare from old region 10798 today! See update below.

[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 inactive to unsettled on September 6. Solar wind speed ranged between 432 and 468 (all day average 450) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 83.4. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 8.6).
Three hour interval K indices: 32422312 (planetary), 33122332 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 3 C and 1 M class events was recorded during the day. Old region 10798 behind the southeast limb produced a long duration C1.3 event peaking at 07:52, a C1.3 flare at 10:18 and a very long duration M1.4 event peaking at 22:02 UTC. This region could produce very significant X class proton flares. Background proton levels have been increasing slowly over the last day as this region approached the limb.

Region 10805 decayed slowly and quietly.

Spotted regions not numbered by NOAA/SEC:
[S590] This region rotated partly into view at the northeast limb on September 6. Location at midnight: N10E84.

Comment added at 18:22 UTC on September 7: Old region 10798 produced one of the largest flare ever recorded today at 17:40 UTC. GOES Xray sensors displayed signs of saturation. While GOES12 has this as an X17 flare the peak was likely close to X20. Previous CMEs from this region have been very fast. Although this occurred at the southeast limb, a significant sideways impact at Earth could occur as early as before midnight tomorrow, although more likely on September 9. Active to severe geomagnetic storming is possible. We will have to wait to see if this was a proton flare as well.

Coronal mass ejections (CMEs)

September 4-6: A CME was observed over the west limbs following a long duration C2 event in region 10803 during the afternoon on September 4. A backsided, large full halo CME was observed after the LDE in old region 10798 behind the southeast limb near noon on September 5.

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 poorly defined recurrent coronal hole (CH186) in the northern hemisphere near the equator was in an Earth facing position on September 5-6. A recurrent trans equatorial coronal hole (CH187) will rotate to an Earth facing position on September 9-11.

Processed TRACE mosaic image from September 6, 2005. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on September 7 and quiet to active on September 8-9 due to effects from CH186. Quiet conditions are likely on September 10-11 becoming quiet to active on September 12-13 when a high speed stream from CH187 reaches Earth.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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.


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 good. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and LT28 Rafaela Argentina. Several stations from Argentina were noted with unusually good signals during the night: 1030, 1070 and 1190 kHz were the best.

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.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10805 2005.08.27 2 2 S12W59 0040 DAO classification was HAX at midnight, area 0010
strange classification by SEC
10806 2005.08.29     S16W58     plage
S588 2005.08.31     N12W49     plage
S590 2005.09.06   1 N10E84 0050 HSX  
Total spot count: 2 3  
SSN: 12 23  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 35.9 (-1.6)
2004.11 113.2 43.5 35.3 (-0.6)
2004.12 94.5 17.9 35.2 (-0.1)
2005.01 102.2 31.3 34.6 (-0.6)
2005.02 97.2 29.2 33.9 (-0.7)
2005.03 89.9 24.5 (33.5 predicted, -0.4)
2005.04 86.0 24.4 (32.2 predicted, -1.3)
2005.05 99.3 42.6 (29.9 predicted, -2.3)
2005.06 93.7 39.6 (28.7 predicted, -1.2)
2005.07 96.4 39.9 (27.7 predicted, -1.0)
2005.08 90.5 36.4 (25.8 predicted, -1.9)
2005.09 77.3 (1) 3.4 (2) (24.2 predicted, -1.6)

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.

[DX-Listeners' Club]