Solar Terrestrial Activity Report

Last major update issued on August 1, 2006 at 04:45 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 quiet to unsettled on July 31. Solar wind speed ranged between 354 and 651 km/s (all day average 489 km/s - increasing 84 km/s over the previous day) under the influence of a high speed stream from CH234.

Solar flux measured at 20h UTC on 2.8 GHz was 72.4. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 11.8).
Three hour interval K indices: 23333223 (planetary), 23333322 (Boulder).

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

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10901 decayed quietly and could soon become spotless.
Region 10902 decayed slowly.

Coronal mass ejections (CMEs)

July 29-31: No partly or fully Earth directed CMEs were detected in LASCO imagery.

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 well defined recurrent trans equatorial coronal hole (CH234) was in an Earth facing position on July 28-30. A recurrent coronal hole (CH235) in the southern hemisphere (with a trans equatorial extension) will likely rotate into an Earth facing position on August 3-4.

Processed SOHO/EIT 284 image at 01:06 UTC on August 1. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on August 1 due to a high speed stream from CH234 becoming quiet to unsettled on August 2-3.

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 poor. Propagation on long distance northeast-southwest paths is fair. From North America Newfoundland stations were noted on 620, 740, 800 and 930 kHz while weak signals could be heard from 1130 WBBR and 1510 WWZN. Propagation was best to southeastern Brazil, Argentina (good signals on 950 and 1190 kHz) and Chile (1180 and 1380 kHz). Radio Bethel (Argentina) was briefly audible on 1671.03 kHz.

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.