Solar Terrestrial Activity Report

Last major update issued on April 11, 2006 at 05:10 UTC.

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

Recent activity

The geomagnetic field was quiet to minor storm on April 10. Solar wind speed ranged between 565 and 734 (all day average 623) km/sec under the influence of a high speed stream from CH219. The high speed stream appeared to be ending during the last hours of the day.

Solar flux measured at 20h UTC on 2.8 GHz was 88.7. The planetary A index was 18 (STAR Ap - based on the mean of three hour interval ap indices: 17.8).
Three hour interval K indices: 45432221 (planetary), 35433222 (Boulder).

The background x-ray flux is at the class A9 level.

At midnight there were 5 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10869 decayed slowly and quietly,
New region 10870 emerged early in the day in the southeast quadrant. There is some slight polarity intermixing in the trailing spots and further development is likely. The region emerged in the center of CH220.
New region 10871 rotated into view at the southeast limb on April 8 and was noticed by SEC two days later. Unfortunately they then combined this region with another region, S844, see below.

Spotted regions not numbered by NOAA/SEC:
[S644] This region emerged in the southeast quadrant on April 10. The leading spot has the same polarity as the single spot in region 10871, which is located 12 degrees further west. Location at midnight: S04E60.
[S645] A new region emerged in the northeast quadrant late on April 10. Location at midnight: N05E08.

Coronal mass ejections (CMEs)

April 8-10: No partly or fully Earth directed CMEs were observed in LASCO imagery. A full halo diffuse CME was observed in LASCO C3 images starting at 12:40 UTC on April 10. Its source was likely backsided.

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 recurrent trans equatorial coronal hole (CH220) will be in an Earth facing position on April 11-13.

Processed SOHO/EIT 284 image at 01:06 UTC on April 11. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet on April 11-13 becoming quiet to minor storm on April 14-16 as a high speed stream from CH220 becomes the major solar wind factor.

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 very poor. Propagation on long distance northeast-southwest paths is fair to good. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Vibración (Venezuela). Early in the night propagation favored Uruguay and Argentina (1540 Radio Món with a fair signal was a big surprise at 23h UTC). Later on stations from Venezuela became dominant while at local sunrise conditions were best to southern Brazil and Uruguay.

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
10866 2006.03.29 1   S05W92 0030 AXX rotated out of view
10867 2006.04.02 1   S15W96 0030 AXX spotless all day!
10868 2006.04.05     S07W71     plage
10869 2006.04.06 15 9 S12W31 0090 EAI classification was EAO at midnight
10870 2006.04.10 1 9 S08E22 0010 AXX classification was CAI at midnight, area 0050
10871 2006.04.10 2 1 S08E52 0050 CAO formerly region S643
classification was HAX at midnight, location: S08E48
S641 2006.04.04     S06W81     plage
S644 2006.04.10   3 S04E60 0030 CAO  
S645 2006.04.10   3 N05E08 0000 BXO  
Total spot count: 20 25  
SSN: 70 75  

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)
2005.01 102.2 31.3 34.6 (-0.6)
2005.02 97.2 29.2 33.9 (-0.7)
2005.03 89.9 24.5 33.5 (-0.4)
2005.04 86.0 24.2 31.6 (-1.9)
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 (24.8 predicted, -1.0)
2005.11 86.3 18.0 (22.7 predicted, -2.1)
2005.12 90.7 41.2 (19.8 predicted, -2.9)
2006.01 83.4 15.4 (16.7 predicted, -3.1)
2006.02 76.5 4.7 (13.6 predicted, -3.1)
2006.03 75.4 10.8 (11.4 predicted, -2.2)
2006.04 93.9 (1) 22.6 (2) (10.7 predicted, -0.7)

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]