Tad Cook, K7RA, Seattle, reports: An extended lull in solar activity persists. The smoothed sunspot minimum occurred last December, but the flurry of moderate sunspot activity in August has not continued.

An event to look forward to is the autumnal equinox, which occurs at 1330 UTC on Tuesday, September 22. We should see a seasonal improvement in HF propagation around that date because the northern and southern hemispheres are bathed in roughly equal solar radiation, enhancing north-south propagation.

Thursday, September 10 was the 20th consecutive day with no sunspots, but Spaceweather.com reported a small sunspot with a Cycle 25 magnetic signature may be forming in the sun’s southeastern quadrant. As of Thursday night it was still too small to merit numbering.

Average daily solar flux barely budged from 69.6 to 69.7. Geomagnetic indicators were very quiet, with average daily planetary A index declining from 13.1 to 4.4. As with last week’s forecast, predicted solar flux is 70 on every day over the next 45 days, September 11 – October 25.

Predicted planetary A index is 5 on September 11 – 17; 8 on September 18 – 19; 5 on September 20 – 22; 8, 10, and 15 on September 23 – 25; 10, 25, 15, and 10 on September 26 – 29; 5 on September 30; 8 on October 1; 5 on October 2 – 14; 8 on October 15 – 16; 5 on October 17 – 19, and 8, 10, 15, 10 and 25 on October 20 – 25.

F.K. Kanda, OK1HH, in the Czech Republic has shared geomagnetic activity forecast for September – October 6.

The geomagnetic field will be:

• quiet on September 11 – 13, 16 – 17, 20 – 21

• quiet to unsettled on September 14, 22 – 25, 29, October 1 – 2

• quiet to active on September 15, 18 – 19, 26 – 27, (October 5 – 6)

• unsettled to active (September 28 – 30; October 3 – 4)

• active to disturbed not expected

Solar wind will intensify on September (15, 19,) 22 – 23, (October 3 – 4)

Note: Parentheses mean lower probability of activity enhancement.

Frank Donovan, W3LPL shared this on September 6:

“Exactly 3 years ago, on September 6, 2017, the sun ejected the strongest solar flare and earth-directed coronal mass ejection (CME) of Solar Cycle 24. Solar region 2673 produced four X-class solar flares, including a massive X-class solar flare of magnitude 9.3, from 1153 to 1210 UTC.

Just over 8 minutes later, powerful hard X-rays from the flare increased D-layer ionization by several orders of magnitude, completely blacking out HF skywave propagation on the daylight side of Earth for about an hour — an event called a “sudden ionospheric disturbance” (SID).

Solar flares are commonly followed by CMEs. Solar region 2673 ejected powerful Earth-directed CMEs on September 6, 2017, causing visible aurora on September 7 and 8, and a severe geomagnetic storm the planetary Kp index reached magnitude 8 on September 8.

See the SpaceWeatherLive.com YouTube presentation.

The strongest solar flare measured in modern times was an X28 flare on October 28, 2003, which blacked out HF skywave propagation on the sunlit side of Earth for several hours. Extremely powerful CMEs on October 28 and 29 caused severe geomagnetic storms on October 29, 30, and 31, and the Kp index reached magnitude 9 on all 3 days.

A 3-hour video from WX6SWW! Coronal Holes and Sources of the Solar Wind — Part 2.

Sunspot numbers for September 3 – 9 were 0, 0, 0, 0, 0, 0, and 0, for a mean of 0. The 10.7-centimeter flux was 70, 69.7, 69.2, 69.5, 70.2, 69.9, and 69.7, with a mean of 69.7. Estimated planetary A indices were 4, 8, 6, 4, 4, 4, and 1, with a mean of 4.4. Middle latitude A index was 3, 9, 7, 5, 5, 4, and 1 with a mean of 4.9.

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

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