Solar Terrestrial Activity Report

Last major update issued on May 17, 2005 at 03:20 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 15, 2005)]

Recent activity

The geomagnetic field was quiet to major storm on May 16. Solar wind speed ranged between 449 and 976 km/sec, still strongly influenced by the CME which arrived early on May 15.

Solar flux measured at 20h UTC on 2.8 GHz was 99.1. The planetary A index was 33 (STAR Ap - based on the mean of three hour interval ap indices: 32.9).
Three hour interval K indices: 46534522 (planetary), 46533422 (Boulder).

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

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 6 C and 2 M class events was recorded during the day.

Region 10759 decayed further and has no penumbra outside of the main penumbra.
Region 10763 added several small spots and lost some penumbral area in the trailing spot section. There is still a magnetic delta structure in the largest trailing penumbra and poor separation between the opposite polarity areas in the leading spot section. Further M class flares are possible. Flares: M1.4/1B at 02:43, C2.9 at 03:36, M1.6 at 09:08, C1.3 at 10:00, C1.8 at 16:06, C2.0 at 16:51, C5.5 at 19:47 and C1.1 at 20:42 UTC.

Coronal mass ejections (CMEs)

May 14-16: 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 (CH166) in the northern hemisphere will likely be in an Earth facing position on May 17. CH166 may be too far to the north to become geoeffective.

Processed SOHO/EIT 284 image at 01:06 UTC on May 17. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected be quiet to minor storm on May 17 and quiet to unsettled on May 18-19.

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 with a poor signal. On other trans Atlantic frequencies only stations from Brazil were noted with the best signal on 1100 kHz.

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.