Solar Terrestrial Activity Report

Last major update issued on April 13, 2006 at 02:55 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 inactive to very quiet on April 12. Solar wind speed ranged between 349 and 448 (all day average 381) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 81.6. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.1).
Three hour interval K indices: 01000111 (planetary), 11001000 (Boulder).

The background x-ray flux is at the class A3 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 was quiet and stable.
Region 10870 decayed slowly and quietly.
Region 10871 was quiet and stable.
Region 10872 was quiet and unchanged.
Region 10873 decayed in the trailing spot section while only minor changes were observed in the leader spots.

Coronal mass ejections (CMEs)

April 10-12: No partly or fully Earth directed CMEs were observed in LASCO imagery.

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 17:59 UTC on April 12. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet on April 13 and 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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation on long distance northeast-southwest paths is fair to poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay. Propagation was best to Venezuela and Newfoundland (a few of the most common stations were audible).

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
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10869 2006.04.06 4 1 S11W61 0040 CSO classification was HSX at midnight
10870 2006.04.10 5 2 S08W05 0020 CSO classification was HSX at midnight, area 0030
10871 2006.04.10 3 3 S08E23 0050 CSO classification was HSX at midnight
10872 2006.04.11 1 1 S07E59 0030 HSX area was 0020 at midnight
10873 2006.04.11 16 10 S04E35 0090 DAI  
S645 2006.04.10     N05W18     plage
Total spot count: 29 17  
SSN: 79 67  

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 92.5 (1) 27.7 (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.


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