Solar Terrestrial Activity Report

Last major update issued on May 26, 2005 at 04:05 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 quiet on May 25. Solar wind speed ranged between 321 and 398 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 83.8. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.5).
Three hour interval K indices: 21211221 (planetary), 21211221 (Boulder).

The background x-ray flux is at the class A7 level.

At midnight there were 3 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10766 developed slowly and quietly.
Region 10767 added several small intermediate spots. C flares are possible.

Spotted regions not numbered by NOAA/SEC:
[S551] This region emerged in the southwest quadrant on May 25. Location at midnight: S08W36.

Coronal mass ejections (CMEs)

May 23-25: 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 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 26. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet on May 26 and most of May 27. Unsettled and active intervals are possible from late on May 27 until May 29 due to effects from CH167.

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) 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.

Propagation

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. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. At least one station from Argentina was audible as well. On other frequencies (930, 1130, 1500, 1510, 1520, 1540 and 1590 kHz) there were only a few stations with weak signals from Argentina and Uruguay.

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.

Monthly solar cycle data

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.