The Australian Bureau of Meteorology’s Space Forecast Centre issued a geomagnetic warning at 0009 UTC on September 4:
“The IMF Bz [Interplanetary Magnetic Field] has been strongly southward over the last 3 hours (2100 UTC on September 3 to present). However, the current solar wind speeds are at moderate levels, which are unfavourable to cause any major geomagnetic disturbance. If the solar wind speeds elevate in the coming 24 hours, active to minor storm conditions are possible. If this happens, there is chance that aurora would be visible during the local night hours of the 4 Sep from Tasmania and other southern most regions of Australia.
“Increased geomagnetic activity expected due to coronal hole high speed wind stream for September 4, 2015.”
Over this reporting week, August 27 through September 2, the average daily sunspot number was 48.3, which is 21.4 points lower than the previous 7 days. Average daily solar flux declined 22.7 points to 97.
New sunspot groups appeared on August 27, 29, 30, 31, September 1, and 3, but activity is still very weak, and the sunspots are not magnetically complex or strong.
Now that we are in early September, we can look at recent monthly averages for sunspot numbers. For May through August the monthly daily sunspot numbers averaged 83, 77.4, 68.5, and 61.7, respectively. As you can see, there has been a steady decline in activity.
For our 3-month moving average of daily sunspot numbers, the past 3 months — June 1 through August 31 — averaged 69.1. This is centered on July 2015. For the past 12 months, the 3-month moving averages of daily sunspot numbers were 108.4, 107, 104.7, 107.8, 98.2, 78.1, 68.2, 72.4, 77.7, 76.3, and 69.1, respectively. According to the same figures, the current sunspot cycle peaked between January and April 2014, when the 3-month moving average centered on those months was 138.5, 146.4, 148.2, and 129.6.
The latest predicted solar flux values for the near term from NOAA/USAF forecasters are 85 on September 4; 90 on September 5-8; 85 on September 9-10; then 95 and 105 on September 11-12; 115 on September 13-22; then 110, 105, and 100 on September 23-25; 90 on September 26-28, and then bottoming out at 85 on September 29 through October 7. Although this is a long way out, flux values are predicted to rise to 115 for October 10-18.
Planetary A index predictions show values of 8, 10, and 9 on September 4-6; then 10, 12, and 9 on September 7-9; then 5 on September 10-11; 12, 15, and 10 on September 12-14; 8, 10 and 5 on September 15-17, then 8, 20 and 10 on September 18-20, 5 on September 21-23, and 15, 10, 5, 8, 20, and 22 on September 24-29. A quiet period with planetary A index at 5 is predicted for October 4-8.
Petr Kolman, OK1MGW, of the Czech Propagation Interest Group predicts geomagnetic conditions will be quiet to unsettled on September 4-5, mostly quiet September 6-8, quiet on September 9-10, quiet to active September 11-13 (with the possibility of disturbed conditions on September 11), quiet to unsettled September 14, quiet to active September 15-16 (possibly disturbed September 15), quiet to unsettled September 17-18, active to disturbed September 19, mostly quiet September 20-21, quiet to active September 22, active to disturbed September 23-24, quiet to unsettled September 25, quiet September 26-28, mostly quiet September 29, and quiet to unsettled September 30.
Petr expects increased solar wind on September 10-13, 15-16, 19, and 22-24.
Spaceweather.com reports that 156 years ago this week, on September 2, 1859 the huge Carrington Event occurred — the monster geomagnetic storm in which a 1 billion ton coronal mass ejection (CME) smashed into Earth, setting fire to telegraph stations around the world. Check Spaceweather.com, using the archive feature in the upper right corner of the site, to select September 2, 2015.
David Moore sent a link to a dramatic video from the Solar Dynamics Observatory, showing sunspot group 2403 breaking up in the past week. David sent another link about solar activity and aurora over the past week:
Slate has posted animation created by stringing together a long series of hand-drawn sunspot maps.
For more information concerning radio propagation, see the ARRL Technical Information. See “What the Numbers Mean, and Propagation Predictions — a brief introduction to propagation and the major factors affecting it” for an explanation of the numbers used in this bulletin. An archive of past propagation bulletins is on the ARRL website, and the website of Carl, K9LA, offers more good information and tutorials on propagation.
Click on “Download this file” to download the archive and ignore the security warning about file format. Pop-up blockers may suppress downloads. (I’ve had better luck with Firefox than with IE).
See monthly propagation charts between four US regions and 12 overseas.
Instructions for starting or ending email distribution of ARRL bulletins are on the ARRL website.
Sunspot numbers for August 27 through September 2 were 46, 52, 50, 50, 50, 49, and 41, with a mean of 48.3. The 10.7 cm flux was 110.2, 109.1, 100.1, 91.6, 91, 89, and 88.2, with a mean of 97. Estimated planetary A indices were 53, 43, 16, 5, 6, 6, and 7, with a mean of 19.4. Estimated mid-latitude A indices were 26, 28, 13, 5, 5, 7, and 10, with a mean of 13.4.
Send me your reports and observations! — Thanks to Tad Cook, K7RA