Solar Terrestrial Activity Report

Last major update issued on May 11, 2005 at 04:35 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 10. Solar wind speed ranged between 445 and 559 km/sec. 

Solar flux measured at 20h UTC on 2.8 GHz was 119.2. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.5).
Three hour interval K indices: 33322222 (planetary), 33322232 (Boulder).

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

At midnight there were 6 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 7 C and 1 M class events was recorded during the day.

Region 10758 developed moderate quickly in the leading and intermediate spot section with most spots inside a huge penumbral area. A magnetic delta structure inside this penumbra is strengthening and an M class flare is possible. Flares: C1.7 at 02:19, C2.0 at 04:00, M1.3 at 05:23 (with an associated moderate type IV radio sweep), C2.2 at 09:05, C1.5 at 12:26 and C1.3 at 14:12 UTC.
Region 10759 was mostly unchanged and remains capable of producing an M class flare. Flares: C1.1 at 16:12 and C5.8/1F at 19:58 UTC.
Region 10761 was quiet and stable.

Spotted regions not numbered by NOAA/SEC:
[S545] A new region emerged in the southeast quadrant on May 9. The region decayed slowly on May 10. Location at midnight: S06E15.
[S546] A new region emerged in the southeast quadrant on May 9 just south of region S545. Slow development was observed on May 10 and the region has mixed polarities. Location at midnight: S12E16.
[S547] This region rotated partly into view at the southeast limb late on May 10. Location at midnight: S16E81.

Coronal mass ejections (CMEs)

May 8-10: No obviously fully or partly potentially geoeffective CMEs were observed.

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 narrow elongated coronal hole in the northern hemisphere near the equator will be in an Earth facing position on May 10-11.

Processed SOHO/EIT 284 image at 19:06 UTC on May 10. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected be quiet to unsettled on May 11-12. Quiet to active is possible on May 13-14 due to a low speed stream from CH164.

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 stations tonight: Radio Cristal del Uruguay and CPN Radio (Perú). both weak weak signals. Signal levels didn't pick up until after local sunrise when propagation favored stations from Argentina (710 Radio 10 and 1190 Radio América both reached a fair signal level).

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.

SEC active region data for May 10 was unavailable at the time of this report.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10758 2005.05.02   35 S08W38 0570 FKI beta-gamma-delta
10759 2005.05.08   12 N12E47 0420 EKO  
10761 2005.05.09   1 N03E47 0010 HRX  
S545 emerged on
  5 S06E15 0030 CAO  
S546 emerged on
  14 S12E16 0070 DAI beta-gamma
S547 visible on
  1 S16E81 0010 AXX  
Total spot count: 56 68  
SSN: 106 128  

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)
2005.05 109.7 (1) 23.6 (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]