Solar Terrestrial Activity Report

Last major update issued on July 26, 2007 at 04:05 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update July 23, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 23, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 23, 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 very quiet on July 25. Solar wind speed ranged between 282 and 354 km/s (average speed was 327 km/s, decreasing 21 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 68.6. The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.3). Three hour interval K indices: 00011110 (planetary), 00011101 (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 23-25: 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 trans equatorial recurrent coronal hole (CH279) was in an Earth facing position on July 21-23. Another trans equatorial recurrent coronal hole (CH280) will rotate into an Earth facing position on July 25-27.

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Processed SOHO/EIT 195 image at 00:00 UTC on July 26. 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 poor. Propagation on long distance northeast-southwest paths is fair.

Monitoring remarks from a location near N58E06: July 26: At 02:30 UTC several stations from North America were audible. A few stations, like 1130 WBBR, had fair to good signals. Then, within minutes, nearly all trans Atlantic signals disappeared. A little later, at LSR, only stations from South America were audible with the best signals from 950 Radio Belgrano, 1220 Rádio Globo and 1500 Radio Dos Mil.

Forecast

The geomagnetic field is expected to be quiet to active on July 26 due to effects from CH279. Mostly quiet conditions are likely on July 27. Another high speed stream (from CH280) could cause unsettled to active conditions on July 29-30.

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.