Solar Terrestrial Activity Report

Last major update issued on April 15, 2006 at 05:35 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 1, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 1, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 1, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update April 3, 2006)]

Recent activity

The geomagnetic field was active to severe storm on April 14. Solar wind speed ranged between 443 and 546 (all day average 492) km/sec under the influence of a strong high speed stream from CH220.

Solar flux measured at 20h UTC on 2.8 GHz was 78.9. The planetary A index was 58 (STAR Ap - based on the mean of three hour interval ap indices: 58.4).
Three hour interval K indices: 46775544 (planetary), 45674444 (Boulder).

The background x-ray flux is at the class A3 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 10871 was quiet and stable.
Region 10872 was quiet. The single penumbra lost a little area.
Region 10873 decayed and could soon become spotless.

Coronal mass ejections (CMEs)

April 12-14: No partly or fully Earth directed CMEs were observed in LASCO imagery.

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 trans equatorial coronal hole (CH220) was in an Earth facing position on April 11-14.

Processed SOHO/EIT 284 image at 19:06 UTC on April 14. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 14-16 under the influence of a high speed stream from CH220.

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

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor to useless. Propagation on long distance northeast-southwest paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. At and near local sunrise propagation was best to Argentina (best signals noted on 700, 710, 950 and 1190 kHz) and Colombia (the Calí stations on 980 and 1230 kHz had good signals).

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.