The K7RA Solar Update


Tad Cook, K7RA, Seattle, reports: Lots of news lately about the solar cycle, but no sunspots. Today, September 18, is the 29th consecutive day with no sunspots.

The news this week was about the Solar Cycle 24 minimum, announced recently as having occurred during December 2019 and indicating the start of Solar Cycle 25. The reason that announcement is just coming out now has to do with the nature of moving averages, which in this case is a smoothed sunspot number, derived from arithmetical averaging of sunspot numbers over a whole year, i.e., half before December and half, to derive a mid-point average.

Recent news stories offer predictions for Solar Cycle 25, such as this one from SpaceRef.

The reporting week of September 10 – 16 gave us an average daily solar flux of 69.2, no significant difference from the previous week’s 69.7. Average daily planetary A index was 5.3, up only a little from 4.4 the previous week. Average daily mid-latitude A index went from 4.9 to 5.4.

Predicted solar flux for the next 45 days (September 18 – November 1) is the same as reported in past recent bulletins, 70 on every day.

Predicted planetary A index is 5 on September 18 – 22; 8, 10, 15, 10, 25, 15, and 10 on September 23 – 29; 5 on September 30 – October 14; 8 on October 15 – 16; 5 on October 17 – 19; then, as in the earlier period, 8, 10, 15, 10, 25, 15, and 10 on October 20 – 26, then back to 5 on October 27 – November 1.

Here’s a geomagnetic activity forecast for September 18 – October 13 from F.K. Janda, OK1HH. The geomagnetic field will be:

  • quiet on September 21-22, October 6-8

  • quiet to unsettled on September 18, October 3-5, 9-10, 13

  • quiet to active on September 19-20, 23-24, 29-30, October 1-2

  • unsettled to active (September 25-28, October 11-12)

  • active to disturbed: not expected

  • Solar wind will intensify on September (19,) 22-23, 27-29, October (3-4,) 11-13

Note: Parentheses mean lower probability of activity enhancement. The predictability of changes remains lower because there are few unambiguous indications.

Steven Rudnick, W1KYB, Santa Fe, New Mexico, asked, “How did they come to the conclusion that we are in a new cycle when the sunspot number has been zero for 27 days now?”

Scientists probably looked at a couple of factors. One is the polarity of sunspots. As the sun transitions from one cycle to the next, the polarity of sunspots changes. It starts with a few sunspots having opposite polarity from sunspots in the recent cycle, then gradually it shifts so eventually the majority have the new cycle polarity.

The other factor is the smoothed sunspot number, which is an average based on an entire year of sunspot numbers. This reduces the noise in the numbers, so it is easier to see the trends.

The smoothed sunspot number for December 2019 would be based on the monthly sunspot numbers for approximately July 2019 through July 2020.

Here’s the data.

If you look at the monthly averages, they jump all over the place.

The monthly averages for September 2019 through March 2020 were 1.1, 0.40, 0.50, 1.5, 6.2, 0.20, and 1.5.

But the smoothed numbers for those same months were 3.1, 2.6, 2, 1.8, 2.2, 2.8, and currently undetermined for March, placing the lowest number in December.

At some point in the future, the current dearth of sunspots over the past month may just look like noise in retrospect. Or maybe not, should it continue. I hope it does not persist.

From the NOAA Space Weather Prediction Center (SWPC), predicted solar flux and sunspot numbers through December 2040.

Here’s NASA’s take on Solar Cycle 25.

Here’s the latest report from Space Weather Woman Tamitha Skov, WX6SWW.

Sunspot numbers for September 10 through 16, 2020 were 0, 0, 0, 0, 0, 0, and 0, with a mean of 0. The 10.7-centimeter flux was 69.3, 68.7, 69.3, 69.8, 68.9, 68.8, and 69.5, with a mean of 69.2. Estimated planetary A indices were 2, 3, 5, 6, 11, 7, and 3, with a mean of 5.3. Middle latitude A index was 2, 2, 6, 7, 10, 8, and 3 with a mean of 5.4.

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. Monthly charts are no longer be updated on this page. For customizable propagation charts, visit the VOACAP Online for Ham Radio website.

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