Solar Terrestrial Activity Report

Last major update issued on May 27, 2005 at 04:45 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 15, 2005)]

Recent activity

The geomagnetic field was inactive to quiet on May 26. Solar wind speed ranged between 292 and 338 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 90.4. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.8).
Three hour interval K indices: 11011111 (planetary), 11011102 (Boulder).

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

At midnight there were 3 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 10766 decayed quickly and could become spotless today.
Region 10767 developed further. Complexity is increasing, particularly in the intermediate spot section where there is not much separating the opposite polarity spots. An M class flare is possible. Flare: C8.6/1F long duration event peaking at 21:39 UTC. A much more interesting event occurred earlier in the day. A long duration B7.5 event peaking at 14:20 UTC was associated with the ejection of a filament and a full halo CME.
New region 10768 emerged in the southwest quadrant on May 25 and was numbered by SEC the next day.

Coronal mass ejections (CMEs)

May 24-25: No obviously fully or partly potentially geoeffective CMEs were observed.
May 26: A full halo CME was observed after a filament eruption in region 10767 during the early afternoon. This CME will likely reach Earth on May 29. Further material was added later in the day after the C8 long duration event in region 10767.

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 (CH167) in the northern hemisphere was in an Earth facing position on May 24-26. CH167 has lost most of its area over the last rotation.

Processed SOHO/EIT 284 image at 01:06 UTC on May 27. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet most of May 27. Unsettled and active intervals are possible from late on May 27 until May 29 due to effects from CH167. The CME observed on May 26 will likely arrive on May 29 and cause active to major storm conditions that day and on May 30.

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 fair to good. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay and Radio Rafaela (Argentina). Quite a few stations were noted on other frequencies, particulalrly above 1350 kHz. 1510 kHz had both Radio Champaquí (Argentina) and Radio Rincón (Uruguay) as well as occasionally a station from Brazil.

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
10765 2005.05.19     N08W29     plage
10766 2005.05.21 7 3 N14E08 0030 DRO classification was BXO at midnight, area 0010
10767 2005.05.21 31 34 S08E12 0140 DAC beta-gamma
classification was DAI at midnight, area 0300
10768 2005.05.26 4 6 S08W48 0020 DRO formerly region S551
Total spot count: 42 43  
SSN: 72 73  

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)
2005.05 100.3 (1) 54.6 (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]