Solar Terrestrial Activity Report

Last major update issued on July 21, 2006 at 05:00 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update July 19, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 19, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 19, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update July 9, 2006)]

Recent activity

The geomagnetic field was inactive to very quiet on July 20. Solar wind speed ranged between 271 and 328 km/s (all day average 283 km/s - increasing 10 km/s over the previous day).

Solar flux measured at 20h UTC on 2.8 GHz was 72.2. The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.0).
Three hour interval K indices: 11001111 (planetary), 11112012 (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 10900 decayed further and had only a single tiny spot left at the end of the day.

Coronal mass ejections (CMEs)

July 18-19: No partly or fully Earth directed CMEs were detected in LASCO imagery.
July 20: A partial halo CME was observed after noon as a result of the eruption of a large filament in the southeast quadrant.

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 trans equatorial coronal hole (CH232) will rotate into an Earth facing location on July 21. This coronal hole has decayed substantially over the past two solar rotations and is currently poorly defined.

Processed SOHO/EIT 284 image at 01:06 UTC on July 21. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet on July 21-22. The CME observed on July 20 could reach Earth during the latter half of July 23 and cause unsettled to active conditions. A low speed stream from CH232 could influence the geomasgnetic field on July 24-25 resulting in some unsettled intervals.

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 fair. Propagation on long distance northeast-southwest paths is good. The MW band was monitored after 23h UTC. 1610 Radio Guaviyś (Argentina) was heard as early as 2320 UTC and almost continuously until 1 hour after LSR, sometimes with an amazingly good signal. Propagation strongly favored Argentina and Uruguay after LSR with good signals from a number of stations (Argentina: 590, 710, 870, 950, 1190, 1350, 1510 and 1540 kHz. Uruguay: 930, 1050, 1130, 1329.85 (Radio Fenix), 1410 and 1470 kHz). Between 01 and 03h UTC quite a few stations from North America were audible with good signals from 590 VOCM, 930 CJYQ, 1030 WBZ, 1130 WBBR, 1510 WWZN, 1520 WWKB, 1540 WDCD and 1560 WQEW.

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.