Solar Terrestrial Activity Report

Last major update issued on July 24, 2006 at 02:30 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update July 19, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 19, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 19, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update July 9, 2006)]

Recent activity

The geomagnetic field was quiet on July 23. Solar wind speed ranged between 274 and 356 km/s (all day average 319 km/s - increasing 13 km/s over the previous day). Solar wind speed began increasing slowly during the last hours of the day, probably under the influence of a high speed stream from CH232.

Solar flux measured at 20h UTC on 2.8 GHz was 76.5. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.5).
Three hour interval K indices: 21211111 (planetary), 22211112 (Boulder).

The background x-ray flux is at the class A4 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 10901 developed slowly and may be capable of C class flare production.

An active region just behind the east limb appears to be fairly active and could generate C flares.

Coronal mass ejections (CMEs)

July 21-23: No partly or fully Earth directed CMEs were detected in LASCO imagery.
July 20: A partial halo CME was observed after noon as a result of the eruption of a large filament in the southeast quadrant.

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 recurrent trans equatorial coronal hole (CH232) was in an Earth facing location on July 21-22. This coronal hole has decayed substantially over the past two solar rotations and is currently poorly defined. A coronal hole (CH233) in the northern hemisphere has poorly defined southward extensions that will be in Earth facing locations on July 23-24.

Processed SOHO/EIT 284 image at 19:06 UTC on July 23. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on July 24-27 due to coronal hole effects and possibly a weak CME impact.

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. Propagation on long distance northeast-southwest paths is poor to fair. 1470 kHz had an unidentfied station from Brazilian dominating before 23h UTC, then Radio Cristal del Uruguay got the best signal and at midnight Radio Vibración (Venezuela) was on top. At 01h UTC the best propagation was towards the northeastern part of North America with 1130 occasionally with a good signal. 1370 WDEA, 1390 WEGP and 1470 WLAM were all there, although with weak signals. Many stations from Newfoundland, Nova Scotia and New Brunswick had fair to good signals.

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
10900 2006.07.14     S06W78     plage
10901 2006.07.22 11 10 N06E56 0130 DAO  
Total spot count: 11 10  
SSN: 21 20  

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)
2005.05 99.3 42.7 28.9 (-2.7)
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 (20.7 predicted, -2.3)
2006.02 76.5 4.7 (18.2 predicted, -2.5)
2006.03 75.4 10.8 (16.4 predicted, -1.8)
2006.04 89.0 30.2 (15.7 predicted, -0.7)
2006.05 80.9 22.2 (14.9 predicted, -0.8)
2006.06 76.5 13.9 (12.7 predicted, -2.2)
2006.07 76.2 (1) 17.9 (2) (11.3 predicted, -1.4)

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]