Solar Terrestrial Activity Report

Last major update issued on May 7, 2005 at 03:30 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update May 6, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 6, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update May 6, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update May 2, 2005)]

Recent activity

The geomagnetic field was quiet on May 6. Solar wind speed ranged between 313 and 397 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 110.4. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.3).
Three hour interval K indices: 10012222 (planetary), 10002222 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 5 C and 1 M class events was recorded during the day. A region behind the northeast limb could produce M class flares.

Region 10756 decayed slowly and will rotate out of view at the southwest limb today. Another minor M class flare is possible. Flares: impulsive C9.3 at 03:14 and impulsive M1.3 at 11:28 UTC.
Region 10758 developed early in the day, significant decay was observed after the long duration event during the afternoon. An M class flare is still possible Flares: C2.2 at 05:53, C1.0 at 09:31, long duration C8.5/2F peaking at 17:05 and C1.0 at 23:42 UTC.

Coronal mass ejections (CMEs)

May 4: No obviously fully or partly potentially geoeffective CMEs were observed.
May 5: A full halo CME (with very faint extensions over the western limbs) was observed in LASCO C3 images beginning at 21:18 UTC. The source of this CME was probably backsided. Interestingly a bright loop was observed just off the northeast limb later in the day. It is, however, uncertain if this observation has any relevance to the CME.
May 6: A full halo CME was observed in LASCO C3 images beginning at 18:18 UTC. Material distribution around the disk suggest a centrally placed backsided source in the northern hemisphere. Another and more interesting moderately fast CME was observed nearly simultaneously with most of the ejected material seen over the southeast limb. This was at least a partial halo CME, the presence of the other CME makes it hard to determine the full extent. Its source was the long duration event in region 10758.

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 large recurrent coronal hole (CH163) in the northern hemisphere was in an Earth facing position on May 6-7.

Processed SOHO/EIT 284 image at 01:06 UTC on May 7. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected be quiet to unsettled on May 7 and most of May 8. During the latter half of May 8 a high speed stream from CH163 should reach Earth and cause unsettled to major storm conditions for the remainder of the day and on May 9-10. The CME observed on May 6 could reach Earth late on May 8 or on May 9. How much it will influence the geomagnetic field is hard to forecast due to the presence of the high speed stream from CH163.

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 stations tonight: CPN radio (Perú), Radio Cristal del Uruguay and Radio Vibración (Venezuela).  From North America the best signals were noted from 1510 WWZN, 1660 WWRU, 1680 WTTM and 1700 WJCC. 

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 6 9 S08W79 0590 DAC beta-gamma
classification was DKC at midnight, area 0350
10758 2005.05.02 40 26 S07E23 0280 EAI beta-gamma
area was 0140 at midnight, location: S08E24
S541 emerged on
    S15W51     plage
Total spot count: 46 35  
SSN: 66 55  

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)
2004.03 112.0 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 35.9 (-1.6)
2004.11 113.2 43.5 (34.8 predicted, -1.1)
2004.12 94.5 17.9 (33.4 predicted, -1.4)
2005.01 102.2 31.3 (30.9 predicted, -2.5)
2005.02 97.2 29.1 (28.3 predicted, -2.6)
2005.03 89.9 24.8 (26.5 predicted, -1.8)
2005.04 86.0 24.4 (24.6 predicted, -1.9)
2005.05 110.7 (1) 12.0 (2) (22.0 predicted, -2.6)

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]