Solar Terrestrial Activity Report

Last major update issued on September 8, 2005 at 04:40 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 active on September 7. Solar wind speed ranged between 365 and 457 (all day average 409) km/sec.

Solar flux measured at 17h UTC on 2.8 GHz was 92.2 (the measurement at 20h UTC was flare enhanced). The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 15.3).
Three hour interval K indices: 43232441 (planetary), 44123331 (Boulder).

The background x-ray flux is at the class C1+ level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was very high. A total of 4 C and 1 X class events was recorded during the day.

Region 10808 rotated partly into view at the southeast limb on September 7. This region is large, compact and extremely complex. Further X10+ class proton flares are likely. Flares: C2.3 at 10:03, C2.4 at 11:23, C9.6 at 12:44, C1.7 and a monster X17+/3B (possible sensor saturation) long duration proton flare peaking at 17:40 UTC. The X flare was associated with a moderate type IV and a strong type II radio sweep. The associated CME is believed to be very fast and wide (no LASCO images available).

Spotted regions not numbered by NOAA/SEC:
[S590] This region rotated partly into view at the northeast limb on September 6. Location at midnight: N10E71.

Coronal mass ejections (CMEs)

September 5-6: 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.
September 7: While no LASCO images for the hours after the monster X flare in region 10808 are currently available, previous CMEs from this region (while on the backside of the sun) were all wide and fast. There is no reason to believe that this CME wasn't as fast and large. Even when considering that this was a limb event, a sideways impact on Earth is possible from late on September 8 until the afternoon on September 9.

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 active on September 8-9 due to effects from CH186. If there is an impact from the likely very large CME associated with the X17 event on September 7, we could see active to major storm conditions on September 9. Quiet to unsettled 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 poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay with a poor to fair signal. Only a few other stations from South America and WDHP on 1620 kHz were observed during the night.

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     S12W72      
10806 2005.08.29     S16W71     plage
10808 2005.09.07 1 5 S12E83 0010 HSX classification was DKC at midnight, area 0800
S588 2005.08.31     N12W62     plage
S590 2005.09.06   1 N10E71 0050 HSX  
Total spot count: 1 6  
SSN: 11 26  

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 79.4 (1) 3.8 (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]