Solar Terrestrial Activity Report

Last major update issued on April 6, 2006 at 04:25 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 minor storm on April 5. Solar wind speed ranged between 298 and 425 (all day average 345) km/sec. Solar wind speed was low during the first half of the day and under the influence of a disturbance with an unidentified source. Then, near noon, a moderately high speed stream from CH218 arrived causing a decrease in geomagnetic disturbance levels for the remainder of the day.

Solar flux measured at 20h UTC on 2.8 GHz was 99.0. The planetary A index was 29 (STAR Ap - based on the mean of three hour interval ap indices: 28.9).
Three hour interval K indices: 34455432 (planetary), 43454322 (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 low. A total of 2 C class events were recorded during the day.

Region 10865 decayed in the intermediate spot section, however, the very large leading penumbra has many umbrae and may be capable of producing a minor M class event.
Region 10866 was quiet and stable.
Region 10867 decayed further in the trailing spot section. Flares: C2.6 at 13:07 and C8.1 at 15:21 UTC.
New region 10868 emerged in the southeast quadrant on April 4 and was numbered the next day by SEC.

Sptted regions not numbered by NOAA/SEC:
[S642] A new region emerged in the southeast quadrant on April 5. Location at midnight: S12E37

Coronal mass ejections (CMEs)

April 3-5: 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 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 19:06 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 unsettled on April 6-8. Unsettled to minor storm 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 very 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). Very few other trans Atlantic stations were audible.

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.