Solar Terrestrial Activity Report

Last major update issued on May 1, 2005 at 06:20 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 unsettled to minor storm on April 30. Solar wind speed ranged between 359 and 622 km/sec under the influence of a high speed stream from CH162.

Solar flux measured at 20h UTC on 2.8 GHz was 106.4. The planetary A index was 21 (STAR Ap - based on the mean of three hour interval ap indices: 20.9).
Three hour interval K indices: 54334333 (planetary), 44334333 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was low. A single C class event was recorded during the day.

Region 10756 developed in the southern and northeastern sections. There is still a magnetic delta structure in the southernmost penumbra and an M class flare is possible.  Flare: C1.0 at 18:24 UTC.
Region 10757 developed and became more complex with positive polarity spots emerging just south of the leading negative polarity area. C flares are possible.

Coronal mass ejections (CMEs)

April 28-29: No obvious fully or partly Earth directed CMEs were observed.
April 30: A faint full halo CME was observed in LASCO C3 images beginning at 17:18 UTC. No obvious frontside activity was observed during the hours before this, and the source was likely backsided.
May 1: A brighter full halo CME was observed in LASCO C3 images beginning at 01:42 UTC. Considerable large scale reshaping of the corona to the south of region 10756 was observed late on April 30 and early on May 1. However, since I couldn't observe any significant eruptive event or a disappearing filament during the relevant time frame, it is at this time uncertain if the CME was backsided (with the same source as the CME observed on April 30) or had its origin near region 10756.

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 was in an Earth facing position on April 27-29.

Processed SOHO/EIT 284 image at 01:06 UTC on May 1. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected be unsettled to major storm on May 1 due to a high speed stream from CH162. Quiet to active is likely on May 2-3. If the CME observed early on May 1 was caused by activity on the visible disk, a CME impact will be possible on May 3.

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 to fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. Thunderstorm activity in the Atlantic made listening difficult. At local sunrise most of the stations noted were from Argentina.

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
10756 2005.04.25 27 40 S07E01 1000 EKC beta-gamma-delta
classification was DKC at midnight
location: S08E03
10757 2005.04.28 6 15 S06W23 0060 DSO beta-gamma
classification was DAI at midnight, area 0100
location: S07W23
S540 emerged on
    S10W06     plage
S541 emerged on
    S15E27     plage
Total spot count: 33 55  
SSN: 53 75  

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 86.0 (1) 41.5 (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]