Solar Terrestrial Activity Report

Last major update issued on April 28, 2005 at 04:50 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 on April 27. Solar wind speed ranged between 350 and 387 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 95.3. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.1).
Three hour interval K indices: 10012221 (planetary), 11011210 (Boulder).

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

At midnight there were 2 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 10756 developed fairly quickly and has two magnetic delta structures in the single huge penumbra. The strongest delta is in the southeastern part while a smaller delta is in the northeast. The region has major flare potential.

Spotted regions not numbered by NOAA/SEC:
[S539] This region emerged quickly in the southeast quadrant ahead of region 10756 on April 27. Location at midnight: S06E15.

Coronal mass ejections (CMEs)

April 25-27: No obvious fully or partly Earth directed CMEs were observed. A partial halo CME was observed late on April 25 and early on April 26. Most of the observed material was distributed rather symmetrically off the southern limbs. The absence of activity in the central southern hemisphere at the time indicates that the source of this CME was 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 coronal hole (CH162) in the northern hemisphere will rotate to an Earth facing position on April 28-29.

Processed SOHO/EIT 284 image at 01:06 UTC on April 28. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected be quiet to unsettled on April 28-29 becoming unsettled to major storm on April 30 or May 1 due to a high speed stream from CH162.

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 poor to fair. Propagation along long distance north-south paths is poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. Several stations from Brazil were noted before midnight UTC. At and just after local sunrise most of the stations audible were from Argentina with the best signals from the Córdoba stations on 700 and 970 kHz and from Radio Diez on 710 kHz. From North America WWZN on 1510 kHz had fair peaks before local sunrise and several of the usual Newfoundland stations were noted as well.

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
10755 2005.04.17 4   S13W54 0010 BXO spotless for several days
10756 2005.04.25 21 26 S06E42 0760 EKC beta-delta
classification was DKC at midnight
location: S07E42
S538 emerged on
    N08W59     plage
S539 emerged on
  6 S06E15 0030 CAI  
Total spot count: 25 32  
SSN: 45 52  

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 84.1 (1) 35.8 (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]