domenica 17 Ottobre 2021
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The K7RA Solar Update

Tad Cook, K7RA, Seattle, reports: Last week, we reported a big increase in activity with the daily sunspot number reaching 124, but by the end of that week all sunspots had disappeared. The sun was blank for several days, but sunspots returned on September 19.

Average daily sunspot numbers this week were 28.7, which was below the 58.3 average reported a week earlier. Average daily solar flux was down by nine points from 87.4 to 78.4.

Geomagnetic indicators were higher, with the highest activity on September 17, when the planetary A index was 24 due to a minor geomagnetic storm triggered by a weak coronal mass ejection. The average daily planetary A index for the week increased from 7 to 9.1, and the average middle latitude A index went from 6.9 to 8.4.

Predicted solar flux for the next month is 90 and 92 on September 24-25; 95 on September 26-29; 92 on September 30; 84 on October 1-5; 82 on October 6; 80 on October 7-8; 78 on October 9-11; 75 on October 12-20; 80 on October 21-22; 82 on October 23-25; 84 and 82 on October 26-27, and 84 on October 28 – November 1.

Predicted planetary A index is 15, 8, and 20 on September 24-26; 35, 20, and 12 on September 27-29; 5 on September 30 – October 3; 8 and 12 on October 4-5; 5 on October 6-9; 12 on October 10; 5 on October 11-17; 8 on October 18-19; 10, 8, and 12 on October 20-22; 10 on October 23-24; 5 on October 25-30, and 8 and 12 on October 31 – November 1.

The autumnal equinox in the Northern Hemisphere occurred at 1920 UTC on September 22. Earth is bathed in approximately equal amounts of solar radiation over the Northern and Southern hemispheres, always a good sign for HF propagation. reported on September 23 that at 0442 UTC, sunspot group AR2871 produced a strong M3 class solar flare. A coronal mass ejection is headed our way but not directly toward earth. “A glancing blow might be possible on September 26-27,” said. If so, then the predicted planetary A index of 35 on September 27 may turn out to be a lower number.

Here’s the geomagnetic activity forecast for September 24 – October 19 from F.K. Janda, OK1HH. The geomagnetic field will be:

quiet on September 29, October 13, 16 – 18
quiet to unsettled on September 24, 27 – 28, October 1, 3 – 4, 7, 9, 12
quiet to active on September 25 ( – 26), 30, October 2, 8, 10 – 11
unsettled to active on October 5 ( – 6), 14 – 15, (19)
Active to disturbed: Nothing predicted
Solar wind will intensify on October (3, 8,) 11, (19)


* Parenthesis means lower probability of activity enhancement.

* Contradictory indications currently reduce the accuracy of the forecast.

N8II sent this update last week from West Virginia: “During the period when the SFI (10.7-cm Solar Flux Index) was near or over 100, conditions to Europe were somewhat disappointing on 15 — most of the time, a short opening of about an hour at 1400 UTC. September 16-17, the SFI was only 73, but there is now a minor to moderate solar storm in progress at 2400 UTC.

“As the storm was beginning, there was definitely enhanced high-band propagation to the higher latitudes. Around 1400 UTC, I easily worked 4S7AB, Sri Lanka on 15 CW, who was peaking S7, my first QSO with central Asia on 15 in a long time. Also, I worked OH0V, Aaland Islands around 1500 UTC, who was about S5. Geoff, GM8OFQ, in the Orkney Islands, north of Scotland (mainland) was easily 20 dB over S-9 on 17-meters SSB at about 1500 UTC on my dipole. I also worked HB0/DL5YM and YL on 15 CW peaking S-9. 7V7V portable on the beach in Algeria called about S-5. By 1600 UTC band conditions had drastically declined, but EU signals were very loud again on 20 at around 2000 UTC, including OH0V on CW at about 20 dB over S-9.”

N0JK wrote on September 17: “In your last propagation report, you mentioned KB0QZ working LU4HK on 10 CW. I think I know what was up. I neglected to send a report of the September VHF contest conditions. Sunday afternoon, September 12, there were reports of sporadic-E on 6 meters. I worked WA8QYJ (EL96) on 50.313 MHz FT8 at 2109 UTC on Es. KF0M (EM17) and WQ0P (EM19) also worked Florida stations on 6-meter Es at that time. I think it is plausible KB0QZ had a sporadic-E link to afternoon TEP on 10 meters. I also saw WW1L (FN54) spotted HC2FG at 2115 on 50.313 MHz. I suspect double-hop Es. There was single-hop 6-meter Es from the Gulf Coast to HC2FG.”

Space Weather Woman Tamitha Skov, WX6SWW, has released a new forecast.

Sunspot numbers for September 16 – 22 were 0, 0, 11, 13, 51, 50, and 76, with a mean of 28.7. The 10.7-centimeter flux was 73.2, 73.4, 73.7, 75, 80, 84.9, and 88.5, with a mean of 78.4. Estimated planetary A indices were 3, 24, 11, 3, 3, 8, and 12, with a mean of 9.1. Middle latitude A index was 3, 19, 14, 2, 4, 6, and 11, with a mean of 8.4.

For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check out this propagation page.

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