Solar Terrestrial Activity Report

Last major update issued on July 21, 2007 at 03:35 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update June 3, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update June 3, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update June 3, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update July 1, 2007)]

Recent activity

The geomagnetic field was quiet to active on July 20. Solar wind speed ranged between 299 and 533 km/s (average speed was 389 km/s, increasing 55 km/s over the previous day). The high speed stream associated with CH278 was observed arriving at ACE just after 05h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 67.3. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 12.3). Three hour interval K indices: 01334322 (planetary), 01434322 (Boulder).

The background x-ray flux is below the class A1 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)

July 18-20: No obvious fully or partly Earth directed CMEs were observed.

Coronal holes

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 (CH278) in the southeastern quadrant was in a geoeffective position on July 15-16. A trans equatorial recurrent coronal hole (CH279) will likely rotate into an Earth facing position on July 22-23.

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Processed STEREO 195 image at 21:45 UTC on July 20. The darkest areas on the solar disk are likely coronal holes.

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 fair to good.

Monitoring remarks from a location near N58E06: July 21: Many stations from Argentina, Brazil and Uruguay were heard until about 10 minutes after LSR when signals disappeared fairly quickly. 1430, 1470, 1510 and 1540 kHz all had at least 2 stations at times.

Forecast

The geomagnetic field is expected to be quiet to unsettled on July 21, perhaps with a few active intervals due to effects from CH278. Quiet conditions are likely on July 22-24. A high speed stream from CH279 could arrive on July 25 and cause unsettled to minor storm conditions that day and on July 26.

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/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.