Tad Cook, K7RA, Seattle, reports: Solar activity quieted this week, with the average daily sunspot number declining from 57.6 to 28.9, and the average daily solar flux softening from 108.1 to 91.9. On December 8 – 10, the sunspot number was 11 on each day, which is the minimum non-zero sunspot number.

Sunspot group 2786 provided some great activity, but it is about to rotate off the sun’s visible surface. But a look at STEREO satellite images on Thursday night (December 10) shows some magnetic complexity about to became geo-effective from the sun’s southern hemisphere. This could mean more great conditions.

The average daily planetary A index went from 6.4 to 4.4, and average daily middle latitude A index went from 5.6 to 3.1.

Predicted solar flux for the next 45 days is 82 on December 11 – 12; 84 on December 13 – 14; 80 on December 15 – 18; 92 on December 19 – 24; 94 on December 25 – 28; 96, 94, and 92 on December 29 – 31; 90 on January 1 – 4; 88 on January 5 – 7; 86 on January 8 – 11; 84, 85, and 88 on January 12 – 14; 92 on January 15 – 20, and 94 on January 21 – 24.

The forecast for the planetary A index shows 12, 8, and 8 on December 11 – 13; 5 on December 14 – 18; 20 and 8 on December 19 – 20; 5 on December 21 – 22; 8, 10, and 8 on December 23 – 25; 5 on December 26 – January 5; 10 and 8 on January 6 – 7; 5 on January 8 – 13; 12, 20, and 8 on January 14 – 16; 5 on January 17 – 18; 8, 10, and 8 on January 19 – 21, and 5 on January 22 – 24.

Daily updates of these numbers are available, typically after 2120 UTC, from the Space Weather Prediction Center.

A coronal mass ejection on December 7 was expected to spark a geomagnetic storm on December 10-11, which is why the planetary A index was predicted at 40, 25, 8, and 8 on December 10-13. This was revised to the forecast of December 10, above. Minnesota Public Radio aired a story on what happened and how we missed the storm.

The ARRL 10-Meter Contest is this weekend, much anticipated because of recent increased solar activity. I was concerned about the forecast from earlier in the week, but now it looks like good conditions are expected. Around this time each December, sporadic-E activity is possible, as well as enhancement from the Geminids meteor shower. This year the shower does not peak until the day after the contest, December 14, but it’s already under way.

Here’s the geomagnetic activity forecast for December 11 – January 5 from F.K. Janda. OK1HH. The geomagnetic field will be:

• quiet on December 13, (29,) January 12, 4

• quiet to unsettled on December 1416, 21, January 5

• quiet to active on December 12, 1718, 2223, 26, 30

• unsettled to active December (11, 24,) 2526, (27,) 31, (January 3)

• active to disturbed December 19 (-20,) 28

• solar wind will intensify on December (11, 19,) 2022, (23,)

• 27 (28-29, January 5)

Note: Parentheses mean lower probability of activity enhancement.

Max White, M0VNG, shared this article about the European Space Agency’s Solar Orbiter.

Tony Dixon, G4CJC, compiles a weekly 10-meter report, which is posted by Southgate Amateur Radio News.

Space Weather Woman Tamitha Skov, WX6SWW, has posted her latest forecast.

Here’s another article about that optimistic Solar Cycle 25 forecast:

“Massive sunspot AR 2786” is the focus of this article in The Arcadian.

Some great images from Sky and Telescope show the transition of sunspot group 2786:

Sunspot numbers for December 3 – 9 were 40, 38, 42, 25, 35, 11, and 11, with a mean of 28.9. The 10.7-centimeter flux was 102.9, 95.8, 99.9, 90.9, 89.5, 82.4, and 82.1, with a mean of 91.9. Estimated planetary A indices were 3, 2, 5, 6, 3, 5, and 7, with a mean of 4.4. Middle latitude A index was 1, 1, 4, 4, 2, 4, and 6, with a mean of 3.1.

For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check out K9LA’s Propagation Page.

A propagation bulletin archive is available. For customizable propagation charts, visit the VOACAP Online for Ham Radio website.

Instructions for starting or ending email distribution of ARRL bulletins are on the ARRL website.

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