Solar Terrestrial Activity Report

Last major update issued on May 6, 2005 at 04:20 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 to unsettled on May 5. Solar wind speed ranged between 318 and 369 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 109.1. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.8).
Three hour interval K indices: 11131221 (planetary), 11132221 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was low. A total of 4 C class events was recorded during the day.

Region 10756 decayed further in the southern and eastern sections. A positive polarity spot emerged just northwest of the main penumbra and appears to have been associated with the C7 flare. A minor M class flare is possible. Flare: impulsive C7.8 at 20:20 UTC.
Region 10758 developed fairly quickly and has become complex with a negative polarity area emerging inside the trailing positive polarity area. M flares are possible. Flares: C1.3 at 03:10, C1.7 at 11:03 and C2.4 at 14:40 UTC.

Coronal mass ejections (CMEs)

May 3: A partial halo CME was observed in LASCO C3 images beginning at 19:42 UTC. The source of this CME was likely backsided.
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.

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 will be in an Earth facing position on May 6-7.

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


The geomagnetic field is expected be quiet to unsettled on May 6-8 becoming unsettled to major storm on May 9-10 due to a 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. Propagation along long distance north-south paths is poor to fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Rafaela (Argentina). Radio Junin (Argentina) was heard at times 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
10756 2005.04.25 11 18 S09W65 0640 EKC beta-gamma
classification was DKC at midnight, area 0420, location: S08W66
10758 2005.05.02 19 41 S06E37 0190 ESO beta-gamma-delta
classification was EAI at midnight, area 0240, location: S08E37
S540 emerged on
    S10W71     plage
S541 emerged on
    S15W38     plage
Total spot count: 30 59  
SSN: 50 79  

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)
2005.05 110.8 (1) 9.9 (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]