Solar Terrestrial Activity Report

Last major update issued on April 20, 2005 at 04:40 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 15, 2005)]

Recent activity

The geomagnetic field was quiet to active on April 19. Solar wind speed ranged between 322 and 373 km/sec under the influence of a weak low speed stream from CH158. The higher speed stream from the better defined eastern part of CH158 arrived late in the day and is causing a significantly stronger disturbance early on April 20.

Solar flux measured at 20h UTC on 2.8 GHz was 78.2. The planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 8.1).
Three hour interval K indices: 22412222 (planetary), 23412223 (Boulder).

The background x-ray flux is at the class A4 level.

At midnight there were 3 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 10752 decayed slowly and quietly.
Region 10754 decayed further and could become spotless today.
Region 10755 was mostly unchanged. A long duration B7 sub flare enhancement late in the day was associated with a CME originating in this region. The CME was well defined off of the southeast limb, however, awaiting image availability, it is at this time uncertain if there were any Earth directed components.

Coronal mass ejections (CMEs)

April 17-19: 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 coronal hole (CH158) in the southern hemisphere was in an Earth facing position on April 15-17. A recurrent  coronal hole (CH159) in the northern hemisphere will be in an Earth facing position on April 19-20. A coronal hole (CH160) in the southern hemisphere will be in an Earth facing position on April 20.

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


The geomagnetic field is expected be quiet to minor storm on April 20 due to a high speed stream from CH158. Quiet to unsettled is likely on April 21 becoming quiet to minor storm on April 22-23 due to effects from CH159 and CH160.

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. Propagation along long distance north-south paths is 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 towards Puerto Rico with stations noted on 1350, 1520, 1600 and 1660 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
Location at midnight Area Classification Comment
10752 2005.04.12 6 3 N03W28 0110 CAO classification was HAX at midnight, area 0070
10753 2005.04.13     N12W84     plage
10754 2005.04.14 4 1 S08W15 0010 CSO classification was AXX at midnight, area 0000
10755 2005.04.17 3 4 S12E49 0020 CAO classification was CSO at midnight
Total spot count: 13 8  
SSN: 43 38  

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 84.5 (1) 28.5 (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]