Solar Terrestrial Activity Report

Last major update issued on August 19, 2006 at 05:40 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update August 6, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update August 6, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update August 6, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update August 6, 2006)]

Recent activity

The geomagnetic field was quiet to active on August 18. Solar wind speed ranged between 290 and 438 km/s (all day average 362 km/s - increasing 38 km/s over the previous day). A solar wind shock was observed at SOHO at 15:41 UTC (with a sudden increase in wind speed from 350 to 435 km/s), probably associated with an unimportant halo CME observed early on August 16. The interplanetary magnetic field was mostly northwards after the arrival of the shock.

Solar flux measured at 20h UTC on 2.8 GHz was 88.5. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 11.8).
Three hour interval K indices: 24222323 (planetary), 14321323 (Boulder).

The background x-ray flux is at the class B1 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 10904 decayed slowly in the trailing spot section. More significantly new positive polarity flux emerged just to the east of the large leader spot. Several new spots formed and the region has become more complex with an increasing chance of an M class flare.

Coronal mass ejections (CMEs)

August 17-18: No partly or fully Earth directed CMEs were detected in LASCO imagery.
August 16: A large Earth directed CME was observed in LASCO images after the LDE in region 10904 during the afternoon.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A small coronal hole in the southern hemisphere is probably located just too far to the south to be geoeffective, it rotated across the central meridian on August 18.

Processed SOHO/EIT 284 image at 13:06 UTC on August 18. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to major storm on August 19 and quiet to minor storm on August 20 due to the arrival of the large CME observed  on August 16 . Quiet to unsettled is likely on August 21-22.

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) Effects from a CME are likely to be observed at 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 fair. Fair to good signals were noted from quite a few stations from the easternmost parts of North America. 1130 WBBR was excellent in peaks while smaller stations like 1310 WLOB and 1370 WDEA had fair signals. Propagation on long distance northeast-southwest paths is poor. Some stations from Argentina were audible after LSR.

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
10903 2006.08.07     S08W78     plage
10904 2006.08.09 19 18 S13W42 0590 FKO classification was FKI at midnight
S671 2006.08.17     N09E19     plage
Total spot count: 19 18  
SSN: 29 28  

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)
2005.06 93.7 39.3 28.8 (-0.1)
2005.07 96.4 40.1 29.1 (+0.3)
2005.08 90.5 36.4 27.4 (-1.7)
2005.09 91.1 21.9 25.8 (-1.6)
2005.10 77.0 8.5 25.5 (-0.3)
2005.11 86.3 18.0 24.9 (-0.6)
2005.12 90.7 41.2 23.0 (-1.9)
2006.01 83.4 15.4 20.8 (-2.2)
2006.02 76.5 4.7 (18.4 predicted, -2.4)
2006.03 75.4 10.8 (16.6 predicted, -1.8)
2006.04 89.0 30.2 (15.9 predicted, -0.7)
2006.05 80.9 22.2 (15.1 predicted, -0.8)
2006.06 76.5 13.9 (12.9 predicted, -2.2)
2006.07 75.7 12.2 (11.4 predicted, -1.5)
2006.08 78.6 (1) 12.4 (2) (11.4 predicted, -0.0)

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]