Solar Terrestrial Activity Report

Last major update issued on May 23, 2007 at 03:00 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 active on May 22. Solar wind speed ranged between 377 and 453 km/s (average speed was 421 km/s, decreasing 37 km/s from the previous day). Wind density was mostly high during the latter half of the day.

Solar flux measured at 20h UTC on 2.8 GHz was 72. The planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 10.8). Three hour interval K indices: 12122343 (planetary), 21232333 (Boulder).

The background x-ray flux is at the class A1 level.

At midnight there were 2 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 10956 decayed further and could soon become spotless.

Spotted regions not numbered by NOAA/SEC:
[S703] This region rotated into view at the southeast limb on May 22. Location at midnight: S09E74.

Coronal mass ejections (CMEs)

May 19-20: Very faint full halo CMEs were observed both days, probably associated with weak activity in and near region 10956.
May 21-22: 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 (CH270) in the southern hemisphere was in an Earth facing position on May 21-23.

Processed STEREO 195 image at 21:32 UTC on May 22. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on May 23 due to a weak CME passage. Unsettled to minor storm is expected for May 24-26 due to a high speed stream from CH270.

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.

Propagation

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.

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% 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.