On October 15 at 2345 UTC, the Australian Space Forecast Centre issued a geomagnetic disturbance warning, which said that continued strengthening of the solar wind stream due to coronal hole effect may lead to isolated periods of minor geomagnetic storms on October 16.

Sunspot numbers during the October 8-14 reporting period were nearly the same as during the previous 7 days. Average daily sunspot numbers went from 37 to 36.9, and average daily solar flux dropped from 93.8 to 87.5

As in previous solar cycles, geomagnetic indicators are high as the cycle trends downward after the peak.

Go to the bottom of WM7D’s Solar Resource Page and note the graph for Ap (planetary A index) progression. If you look at the graph just above that for solar flux, see how the Ap index is high after the peak of solar flux or sunspot numbers.

From last week to this week, average daily planetary A index went from 24.3 to 25.1, and average mid-latitude A index moved from 15.7 to 17.6.

Predicted solar flux is 105 on October 16; 110 on October 17; 120 on October 18-21; 115 on October 22-23; 120 on October 24; 125 on October 25-26; then 130, 120, and 110 on October 27-29; 100, 90, and 85 on October 30-November 1; 80 on November 2-6; 85 on November 7-8, and 90 on November 9-11. Solar flux then rises to 130 on November 23 and drops below 100 after November 26.

Predicted planetary A index is 18, 15, and 12 on October 16-18; 8 on October 19-20; 5 on October 21-27; then 8, 12, and 10 on October 28-30; 8 on October 31-November 2; 20 on November 3; 15 on November 4-5; then 12, 8, 20, 15, and 18 on November 6-10; 20 on November 11-12; 15 on November 13, and 8 on November 14-18.

OK1MGW of the Czech Propagation Interest Group says to expect a quiet to active geomagnetic field on October 16-17, quiet to unsettled on October 18, mostly quiet October 19-20, quiet to unsettled October 21, quiet on October 22-26, mostly quiet October 27, quiet to unsettled October 28-30, quiet to active October 31 through November 1, active to disturbed November 2-5, quiet to unsettled November 6, quiet to active November 7-9, and quiet to unsettled November 10-11.

David Moore sent this from Space.com. “The sun has sprung a leak. A hole in the topmost layer of the sun and its magnetic field, the size of 50 Earths, is letting loose an ultrafast solar wind that has kicked off several nights of auroras down on Earth.”

Spaceweather.com has posted an image of the huge coronal hole.You can click on the image to zoom in. The white lines represent magnetic lines of force. Current images of the sun at various wavelengths are on the Atmospheric Imaging Assembly website.

The ARRL Technical Information Service has more information concerning radio propagation. For an explanation of the numbers used in this bulletin, see the article, “What the Numbers Mean, and Propagation Predictions — a brief introduction to propagation and the major factors affecting it,” by Carl Luetzelschwab, K9LA. An archive of past propagation bulletins is available. K9LA has information and tutorials on propagation on his website.

My own archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format. Click on “Download this file” to download the archive, and ignore the security warning about file format. Pop-up blockers may suppress the download.

Monthly propagation charts between four US regions and 12 overseas locations are also available on the ARRL website, as are instructions for starting or ending e-mail distribution of ARRL bulletins.

Sunspot numbers for October 8 through 14 were 24, 11, 22, 36, 51, 58, and 56, with a mean of 36.9. The 10.7 cm flux was 79.7, 81.2, 81.4, 84.6, 89.1, 95.6, and 100.7, with a mean of 87.5. Estimated planetary A indices were 56, 26, 12, 12, 22, 25, and 23, with a mean of 25.1. Estimated mid-latitude A indices were 41, 15, 9, 8, 16, 18, and 16, with a mean of 17.6.