Solar Terrestrial Activity Report

Last major update issued on May 20, 2007 at 04:00 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, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 6, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update May 6, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update May 18, 2007)]

Recent activity

The geomagnetic field was quiet to unsettled on May 19. Solar wind speed ranged between 466 and 660 km/s (average speed was 570 km/s, increasing 136 km/s over the previous day) under the influence of a high speed stream from CH269.

Solar flux measured at 20h UTC on 2.8 GHz was 74.8. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 11.5). Three hour interval K indices: 23322333 (planetary), 23332323 (Boulder).

The background x-ray flux is at the class A2 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10956 decayed losing both spots and penumbral area, particularly in the northern part. The main penumbra decreased in size as well, however, opposite polarity spots are rather close to each other. An M class flare is possible. A B9.5 event peaking at 13:02 UTC had its origin in a filament eruption near this region. The event was associated with a type II radio sweep and possibly a CME (no LASCO images covering the time of interest are currently available).

Coronal mass ejections (CMEs)

May 17-19: No obvious fully or partially Earth directed CMEs were observed in available LASCO imagery.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH269) in the southern hemisphere was in an Earth facing position on May 15-16. Another recurrent coronal hole (CH270) in the southern hemisphere will likely rotate into an Earth facing position on May 21-23.

Processed STEREO 195 image at 20:52 UTC on May 19. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on May 20-21. If a CME was associated with the erupting filament just after noon on May 19, a solar winf shock would likely be observed on May 22. If there was no CME quiet conditions are likely on May 22-23. Unsettled to minor storm is expected for May 24-26 due to a high speed stream from CH270.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)

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) Effects from a CME are likely to be observed at 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.


Daily monitoring will not resume until a local noise problem (related to construction work on a neighboring property) has been fixed. Occasional monitoring reports will be submitted when propagation is good.

April 8, 2007: Stations from the Canadian Atlantic provinces had strong signals during the night. Some stations from the northeastern USA and from Florida did well too, in particular 1510 WWZN was impressive.

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
10956 2007.05.14 21 22 N02W06 0150 DAC beta-gamma-delta
10957 2007.05.16 3   S05W60 0030 CRO classification was CAO at midnight
Total spot count: 24 22  
SSN: 44 32  

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)
2006.02 76.5 4.9 18.6 (-2.2)
2006.03 75.4 10.6 17.4 (-1.2)
2006.04 89.0 30.2 17.1 (-0.3)
2006.05 80.9 22.3 17.3 (+0.2)
2006.06 76.5 13.9 16.3 (-1.0)
2006.07 75.7 12.2 15.3 (-1.0)
2006.08 79.0 12.9 15.6 (+0.3)
2006.09 77.8 14.4 15.6 (+0.0)
2006.10 74.3 10.4 14.2 (-1.4)
2006.11 86.3 21.5 (12.7 predicted, -1.5)
2006.12 84.5 13.6 (12.0 predicted, -0.7)
2007.01 83.3 16.9 (11.5 predicted, -0.5)
2007.02 77.7 10.6 (11.2 predicted, -0.3)
2007.03 72.2 4.8 (11.1 predicted, -0.1)
2007.04 72.4 3.7 (11.6 predicted, +0.5)
2007.05 76.9 (1) 16.6 (2) (11.7 predicted, +0.1)

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% lower.

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]