Solar Terrestrial Activity Report

Last major update issued on April 6, 2005 at 03:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 4, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 4, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 4, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update April 2, 2005)]

Recent activity

The geomagnetic field was unsettled to severe storm on April 5. Solar wind speed ranged between 497 and 700 km/sec under the influence of a high speed stream from CH154.

Solar flux measured at 20h UTC on 2.8 GHz was 88.3. The planetary A index was 48 (STAR Ap - based on the mean of three hour interval ap indices: 47.6).
Three hour interval K indices: 77533334 (planetary), 66533334 (Boulder).

The background x-ray flux is at the class A8 level.

At midnight there were 4 spotted regions on the visible solar disk. The solar flare activity level was low. A single C class events were recorded during the day.

Region 10747 lost spots and penumbral area in the trailing spots section. Positive polarity flux emerged in the central part of the region and just south of an area with negative polarity. Further development in this area could cause a magnetic delta structure to form. Flare: C1.1 at 20:07 UTC.
Region 10748 decayed and could soon become spotless
Region 10749 decayed slightly and was quiet.
New region 10750 rotated into view at the southeast limb.

Coronal mass ejections (CMEs)

April 3-5: No obvious fully or partly Earth directed CMEs were observed.

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 coronal hole (CH154) in the northern hemisphere was in an Earth facing position on March 31-April 2. This coronal hole has decayed significantly over the last rotation and lost about half of its area. A coronal hole (CH155) in the southern hemisphere was in an Earth facing, potentially geoeffective, position on April 3. A small trans equatorial coronal hole (CH156) was in an Earth facing position on April 5.

Processed SOHO/EIT 284 image at 19:06 UTC on April 5. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on April 6 as the high speed stream from CH154 becomes less geoeffective. Quiet to unsettled is expected for April 7-8 although April 8 could see an active interval or two due to a low speed stream from CH156.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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) Material from a CME is likely to impact 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 to useless. Propagation along long distance north-south paths is poor to fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). Almost all other trans Atlantic stations noted were from Venezuela, Unión Radio Noticias on 640 and Radio Coro on 780 kHz had the best 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
10747 2005.03.31 12 10 S05W47 0130 DAI beta-gamma
10748 2005.03.31 2 1 N12W06 0020 AXX area was 0010 at midnight
10749 2005.04.03 1 2 S06E38 0020 HAX location S05E36
10750 2005.04.05 1 1 S08E84 0120 HAX classification was HSX at midnight, area 0090
location S06E77
S529 emerged on
    S08W67     plage
S530 emerged on
    N07W61     plage
Total spot count: 16 14  
SSN: 56 54  

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)
2004.02 107.0 45.8 49.3 (-2.7)
2004.03 112.0 49.1 47.1 (-2.2)
2004.04 101.2 39.3 45.5 (-1.6)
2004.05 99.8 41.5 43.8 (-1.7)
2004.06 97.4 43.2 41.6 (-2.2)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 (35.6 predicted, -1.9)
2004.11 113.2 43.5 (33.9 predicted, -1.7)
2004.12 94.5 17.9 (31.6 predicted, -2.3)
2005.01 102.2 31.3 (28.9 predicted, -2.7)
2005.02 97.2 29.1 (26.5 predicted, -2.4)
2005.03 89.9 24.8 (24.7 predicted, -1.8)
2005.04 82.5 (1) 6.6 (2) (22.9 predicted, -1.8)

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% less.

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]