Solar Terrestrial Activity Report

Last major update issued on April 7, 2006 at 02:45 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 active on April 6. Solar wind speed ranged between 357 and 441 (all day average 394) km/sec. Solar wind speed peaked early in the day, then decreased slowly after 09h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 98.9. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 9.6).
Three hour interval K indices: 13422212 (planetary), 23422211 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 5 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 2 M class events were recorded during the day.

Region 10865 decayed further with only small spots remaining in what was the intermediate spot section, The large penumbra still has many umbrae but is more symmetrical than it was a day ago. There is a chance of another minor M class flare. Flares: impulsive M1.4 at 0533 and M1.2 at 20:42 UTC.
Region 10866 was quiet and stable.
Region 10867 decayed further and was quiet.
Region 10868 decayed and could soon become spotless.
New region 10869 emerged in the southeast quadrant on April 5 and was numbered the following day by SEC. The region developed slowly on April 6.

Coronal mass ejections (CMEs)

April 4-6: 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 moderately large trans equatorial coronal hole (CH219) will be in an Earth facing position on April 6-8.

Processed SOHO/EIT 284 image at 19:06 UTC on April 6. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 7-8. Unsettled to minor storm conditions are likely on April 9-11 due to effects from CH219.

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 very poor. Propagation on long distance northeast-southwest paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. On other frequencies most of the TA stations audible from Uruguay (best was 610 Radio Rural and 930 Radio Montecarlo) and Argentina (best reception on 950 kHz).

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
10865 2006.03.28 25 16 S11W60 0530 EKC classification was DKO at midnight, area 0470
10866 2006.03.29 6 6 S06W36 0120 CAO  
10867 2006.04.02 11 6 S16W39 0080 DSI classification was DSO at midnight
10868 2006.04.05 6 5 S07W19 0040 DSO classification was CRO at midnight, area 0020
10869 2006.04.06 7 7 S12E24 0030 BXO formerly region S642
classification was CAO at midnight
S639 2006.04.03     S23W69     plage
S641 2006.04.04     S06W29     plage
Total spot count: 55 40  
SSN: 105 90  

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 96.0 (1) 14.7 (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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