Solar Terrestrial Activity Report

Last major update issued on April 5, 2006 at 03:05 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 quiet to unsettled on April 4. Solar wind speed ranged between 276 and 318 (all day average 296) km/sec. The interplanetary magnetic field has been weakly to moderately southwards since 07h UTC on April 4. A weak geomagnetic disturbance is in progress.

Solar flux measured at 20h UTC on 2.8 GHz was 99.5. The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 6.9).
Three hour interval K indices: 00132223 (planetary), 01232322 (Boulder).

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

At midnight there were 5 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 10865 lost the trailing spots and decayed in the intermediate spot section. The leading penumbra became very large after the merger of the two major penumbrae.
Region 10866 developed slowly. A positive polarity area has emerged just ahead of the leader spots.
Region 10867 decayed and was quiet.

Sptted regions not numbered by NOAA/SEC:
[S640] This region emerged in the southeast quadrant on April 4. Location at midnight: S07E07.
[S641] A new region emerged near the central meridian on April 4, approximately midway between regions 10866 and S640. Location at midnight: S06W03.

Coronal mass ejections (CMEs)

April 2-4: No partly or fully Earth directed CMEs were observed in LASCO imagery. An apparently full halo (complex) CME was observed beginning in LASCO C3 images at 09:42 UTC on April 4. With no flares or disappearing filaments observed during the hours immediately before this, the CME source was likely backsided.

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 small coronal hole (CH218) in the northern hemisphere may have been in an Earth facing position on April 3. A moderately large trans equatorial coronal hole (CH219) will likely rotate to an Earth facing position on April 6-8.

Processed SOHO/EIT 284 image at 01:06 UTC on April 5. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on April 5, quiet to unsettled on April 6-8. Unsettled to active conditions are likely on April 9-11 due to effects from CH219.

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 poor. Propagation on long distance northeast-southwest paths is poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). From North America only stations located on Newfoundland were audible at 02:30 UTC.

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.