Solar Terrestrial Activity Report

Last major update issued on April 24, 2005 at 04:35 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 4, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 4, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 4, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update April 15, 2005)]

Recent activity

The geomagnetic field was quiet on April 23. Solar wind speed ranged between 454 and 584 km/sec under the influence of a weak high speed stream from CH160.

Solar flux measured at 20h UTC on 2.8 GHz was 79.3. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.3).
Three hour interval K indices: 11222222 (planetary), 11222432 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

April 21-23: No obvious fully or partly Earth directed 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 coronal hole (CH160) in the southern hemisphere was in an Earth facing position on April 20. A small trans equatorial coronal hole (CH161) was in an Earth facing position on April 23.

Processed SOHO/EIT 284 image at 19:06 UTC on April 23. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected be quiet to unsettled on April 24 due to effects from CH160. Quiet is likely on April 25 while a few unsettled intervals could be observed on April 26 due to weak effects from CH161.

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 stations tonight: Radio Cristal del Uruguay and Radio Rafaela (Argentina), both with weak signals. On other frequencies a few stations from Puerto Rico and Argentina (Radio Córdoba 700, Radio Diez 710, Radio del Plata 1030 kHz) were heard.

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.