Solar Terrestrial Activity Report

Last major update issued on April 30, 2005 at 05:15 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 to active on April 29. Solar wind speed ranged between 321 and 404 km/sec. The first effects from a high speed stream associated with coronal hole CH162 were observed at ACE at 15:30 UTC. Solar wind speed has since then increased and is, when I write this, near 500 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 105.0. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 11.6).
Three hour interval K indices: 11322244 (planetary), 11323344 (Boulder).

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

At midnight there were 4 spotted regions on the visible solar disk. The solar flare activity level was low. A single C class event was recorded during the day.

Region 10756 developed slowly and added penumbral area in the southern and eastern sections of the huge penumbra. The southern part of the penumbra appears to be splitting off from the main penumbral area. This part of the region is the most complex as there is little distance between opposite polarity spots. A major flare is possible. Flare: C1.7 at 20:41 UTC.
Region 10757 decayed in the leader spots while slow development was observed in the eastern section.

Spotted regions not numbered by NOAA/SEC:
[S540] This region emerged to the west of region 10756 on April 28. Location at midnight: S10E07.
[S541] A new region emerged in the southeast quadrant on April 29. Location at midnight: S15E40.

Coronal mass ejections (CMEs)

April 27-29: 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 recurrent coronal hole (CH162) in the northern hemisphere was in an Earth facing position on April 27-29.

Processed SOHO/EIT 284 image at 01:06 UTC on April 29. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected be unsettled to major storm on April 30 and May 1 due to a high speed stream from CH162. Quiet to active is likely on May 2.

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. Near local sunrise only a few stations from Brazil were noted with Rádio 9 de Julho on 1600 kHz having the best signal.

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.