Solar Terrestrial Activity Report

Last major update issued on July 19, 2007 at 02:20 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 very quiet on July 18. Solar wind speed ranged between 344 and 383 km/s (average speed was 352 km/s, decreasing 51 km/s from the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 69.6. The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.9). Three hour interval K indices: 11001011 (planetary), 11101111 (Boulder).

The background x-ray flux is below the class A1 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10963 decayed slowly and quietly. The region is about to rotate over the west limb.

Coronal mass ejections (CMEs)

July 16-18: 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 potentially geoeffective position on July 15-16. A trans equatorial recurrent coronal hole (CH279) will likely rotate into an Earth facing position on July 23-24.

.

Processed STEREO 195 image at 23:15 UTC on July 18. 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 19: 1470 kHz was again the most lively frequency. Several stations were noted with Radio Cristal del Uruguay dominating. At times LT28 Rafaela Argentina and at least one unidentified Argentinian had fair signals.

Forecast

The geomagnetic field is expected to be quiet most of July 19. A high speed stream from CH278 could arrive on July 19 and cause some unsettled and active intervals until July 21. Quiet conditions are likely on July 22-24.

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.