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The K7RA Solar Update


We observed a return of sunspot activity during the past reporting week (September 6-12), with spots on four days, but not consecutive. Sunspots were visible on September 8-9 and 11-12. Average daily sunspot numbers increased to 7.6, compared to zero over the previous seven days.

Average daily solar flux increased from 67.8 to 68.6, and planetary A index doubled from 6.3 to 12.6, while mid-latitude A index went from 5.9 to 10.

The September 13 forecast predicted solar flux at 70 on September 14, 68 on September 15-22, 67 on September 23-24, 68 on September 25 through October 6, 70 on October 7-9, 68 on October 10-19, 67 on October 20-21, 68 on October 22-28.

The same forecast over the same period supposes planetary A index at 8 on September 14-15, 10 and 8 on September 16-17, 5 on September 18-21, 12 and 8 on September 22-23, 5 on September 24-30, then 8 and 10 on October 1-2. 5 on October 3-6, then 12, 35, 15, 12, 12, 8, 5, 10 and 8 on October 7-15, 5 on October 16-18, then 12 and 8 on October 19-20, 5 on October 21-27 and 8 on October 28.

As recently as September 9, the US Air Force predicted a rise of solar flux to 75 on September 17 before dropping below 70, followed by flux values of 70 on October 7-9. The day before, on September 8 the forecast showed flux values of 70 through September 16, 75 on September 17, and 72 on September 18-22. Predicted solar flux was 75 for October 10-14. This was considerably more optimistic than the latest forecast.


From OK1HH:

Geomagnetic activity forecast for the period September 14 until October 10, 2018

Geomagnetic field will be:

Quiet on September 17, 19

Quiet to unsettled on September 18, 20, 24, October 3

Quiet to active on September 14-15, 25-30, October 4-6, 10

Unsettled to active on September 16, 23, October 1-2, 9

Active to disturbed on September (21) -22, October 7-8

Solar wind will intensify on September 14-16, (21,) 22-24, (25), 29. October 1-2, 6-9


- Parenthesis means lower probability of activity enhancement.

F. K. Janda, OK1HH


Max White sent this link from the Financial Times about solar flares on September 9:

Here is the latest from Dr. Tamitha Skov, WX6SWW, on September 11:

“My newest ‘forecast shorty’ came out on You Tube today as we were passing the peak of this solar storm. As I feared (and mentioned on Twitter and on Patreon numerous times), we did reach G2-level storm conditions. In fact, we remained at G2-levels for over 6 hours. This meant emergency communication over the amateur radio bands was non-existent. Luckily, it looks like the worst is now over. This is good news as several hurricane watch nets are activating as early as tomorrow in anticipation of Hurricane Florence. However, the bad news is the fast solar wind is ongoing, and it will take several days yet for the radio bands to fully recover. Let’s hope they do before this Category 4 storm makes landfall. 

“Since becoming an Amateur Radio operator myself this summer (my call sign is now WX6SWW), I have really begun to appreciate the extent that Space Weather thwarts emergency responders during hurricane season. Even though I do not live on a coast threatened by hurricanes-- Los Angeles hardly gets any rain at all, let alone a hurricane-class storm-- like many, I am beginning to dread this time of year. The concern worsens when I read articles published in reputable weather journals that talk about the intensification of hurricanes in the coming years. For all our sakes, I hope that climate scientists determine a Category 6 for hurricanes is not warranted (see the picture above). Until then, articles like this one will continue to make me very nervous. It really makes me wonder what the peak of the hurricane season will be like in a few years when solar activity begins to rise. 

“Again, a huge debt of gratitude goes to the Patreon members, who are making these forecast shortys possible. Frequent forecast updates such as these prove so critical at times like now. Thank you for helping to keep communities aware so they can stay safe. You are my heroes.” 

See her latest video here:

For more information concerning radio propagation, see the ARRL Technical Information Service at For an explanation of numbers used in this bulletin, see
An archive of past propagation bulletins is at More good information and tutorials on propagation are at

Monthly propagation charts between four USA regions and twelve overseas locations are at 

Instructions for starting or ending email distribution of ARRL bulletins are at 

Sunspot numbers for September 6 through 12, 2018 were 0, 0, 16, 12, 0, 14, and 11, with a mean of 7.6. 10.7 cm flux was 67.4, 67.5, 68.7, 68.4, 69, 69.4, and 69.7, with a mean of 68.6. Estimated planetary A indices were 6, 5, 5, 7, 21, 35, and 9, with a mean of 12.6. Estimated mid-latitude A indices were 5, 5, 5, 6, 15, 24, and 10, with a mean of 10.