Solar Terrestrial Activity Report

Last major update issued on April 6, 2010 at 03:25 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update October 4, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update October 4, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update October 4, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update April 2, 2010)]

The geomagnetic field was unsettled to severe storm on April 5. Solar wind speed ranged between 465 and 832 km/s, at first under the influence of a high speed coronal hole stream. SOHO observed a strong solar wind shock at 07:59 UTC, the arrival of the CME observed on April 3 after just 46 hours in transit. The solar storm caused active to severe storming for the remainder of the day.

Solar flux measured at 20h UTC on 2.8 GHz was 79.3. The planetary A index was 49 (STAR Ap - based on the mean of three hour interval ap indices: 48.6). Three hour interval K indices: 34476544 (planetary), 24475432 (Boulder).

The background x-ray flux is at the class A5 level.

At midnight there were 3 spotted regions on the visible solar disk.

Region 11059 developed new spots early in the day, then began to decay again.
Region 11060 decayed slowly and quietly.
New region 11061 emerged quickly in the northwest quadrant. C flares are possible. This region had spots already on April 3 but had lost the spots by the next day.

April 4-5: No obvious Earth directed CMEs were observed in LASCO or STEREO images.
April 3: A long duration event in region 11059 was associated with at least a partial halo CME.

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH398) in the northern hemisphere was in an Earth facing position on April 3-4.

Processed SOHO/EIT 195 image at 21:36 UTC on April 5. The darkest areas on the solar disk are likely coronal holes.

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is very poor. Propagation on long distance northeast-southwest paths is fair.

The geomagnetic field is expected to be unsettled to major storm on April 6 due to CME effects and quiet to active on April 7-8 due to effects from CH398.

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.

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/SWPC. 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 SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers.

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/SWPC) sunspot number. The official international sunspot number is typically 30-50% lower.
3) Running average based on the daily SWPC ap indices. Values in red are based on official NGDC ap indices.

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.