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The K7RA Solar Update


Tad Cook, K7RA, Seattle, reports: Sun watchers saw no spotless days this week. Average daily sunspot numbers rose from 17.7 last week to 21.7 for the August 19 – 25 reporting week. Average daily solar flux increased from 73.8 to 78.5.

Geomagnetic indicators were quiet, with average daily planetary A index declining from 6.1 to 4.7, and average daily middle latitude A index dropping from 7.6 to 5.7.

We are less than one month away from the autumnal equinox in the Northern Hemisphere on Wednesday, September 22. On that day, both hemispheres will be bathed in equal measures of solar radiation, always a positive for HF propagation.

Predicted solar flux is 90 on August 27 – September 2; 85 on September 3; 73 on September 4 – 11; 74 on September 12 – 15; 76 on September 16 – 18; 77 on September 19 – 20; 76 on September 21; 75 on September 22 – 29, and 73 on September 30 – October 8.

Predicted planetary A index is 16, 12, 10, and 8 on August 27 – 30; 5 on August 31 – September 1; 8 and 12 on September 2 – 3; 5 on September 4 – 10; 10 and 8 on September 11 – 12; 5 on September 13 – 18; 8 on September 19 – 20; 15 and 10 on September 21 – 22; 7 on September 23 – 24; 5 on September 25 – 28; 8 and 12 on September 29 – 30, and 5 through the first week in October.

I find it encouraging that the above solar flux forecast from USAF and NOAA was revised upward over the past few days and that the sunspot number (47) on Thursday, August 26, was much higher than the average daily sunspot number (21.7) over the previous 7 days.

Here’s the geomagnetic activity forecast for August 27 – September 21, from F.K. Janda, OK1HH.

The geomagnetic field will be:

  • quiet on September 1, 5, 10, 14 – 18

  • quiet to unsettled on August 28, 31, September 2 – 4, 6 – 9, 19 – 20

  • quiet to active on August 29 – 30, September 11 – 13, 21

  • unsettled to active August (27)

  • active to disturbed, nothing predicted

Remarks: Parenthesis means lower probability of activity enhancement.

At 0839 UTC on August 26, the Australian Space Forecast Centre issued a geomagnetic warning.

“A weak, slow-moving CME [coronal mass ejection] associated with a disappearing solar filament on 23 August may have a glancing impact at Earth late on the UT day of 26 or into 27 August. Mildly elevated geomagnetic activity may occur following the impact. Another weak, slow-moving CME observed occurring toward the middle of the UT day on 24 August appears to be primarily eastward, although there is a chance it may also have a glancing impact at Earth during 27 August, potentially resulting in mildly elevated geomagnetic activity.”

Darrell Emerson, AA7FV wrote:

“I have a question about a possible 17-meter propagation anomaly between my location (AA7FV in Tucson, DM42pg, 32.3° N, 110.7° W) and the NCDXF beacon W6WX (CM97ae). According to, W6WX is at a bearing of 301° and 1,158 kilometers from AA7FV. Sunset at W6WX is 0249 UTC, and sunset at AA7FV is 0158 UTC.

“I have been using the program Faros to look at the propagation times from various NCDXF beacons. As you know, the NCDXF beacons are time-synchronized using GPS, and so by looking at the arrival times of transmissions from a given beacon, it is easily possible to distinguish between short-path and long-path propagation. This is what the program Faros does.

“As a check, here is data taken at the same time with the same setup on the beacon ZL6B, which shows no anomaly. You can see that I was receiving the beacon from about 0000 UTC until about 0430 UTC. The propagation delays line up precisely with the delay (about 39 ms) expected for short-path propagation. The expected long-path delay would be nearly 100 ms, but no signals are observed with that delay during this time period.”

[Darrell sent graphics that I am unable to reproduce here, but you could email him via his address on, if you want a copy.]

I referred his question to Carl, K9LA, who responded:

“ZL6B sunrise is around 1906 UTC, so I would have expected that you’d see him again later in the day (a bit after 1906 UTC). But perhaps the MUF wasn’t high enough at that time. Or something else was going on. Dropping out around 0430 UTC is understandable, as your sunset is around 0200 UTC and the MUF was slowly dropping until ZL6B (still in daylight) went away around 0430 UTC.

“As for the W6WX results, being only 1,158 kilometers from you says a relatively high elevation angle would be required on the true great circle path. And that says the MUF over that path would not likely be high enough for normal refraction at a high elevation angle on 18 MHz (since we’re just starting to come out of solar minimum). So, your comment about an unusual ionized cloud (or an enhanced area in the ionosphere) is a possible explanation.

“The 20 ms or so delay suggests an off-great circle path from an enhanced area of ionization. And my guess is that this area was south of you and W6WX as that puts it closer to the equatorial ionosphere, where more interesting short-term events happen than north of your location. It’s too bad that the azimuth arrival angle isn’t measured.

“If you’re interested in some more Faros results, check out these documents: and”

By the way, Carl says he accidentally deleted an email from someone named Edgar in Toronto who had questions about VOACAP, and now he has no way to respond. If you are Edgar, please contact K9LA.

Ken Brown, N4SO (EM50tk), in Alabama reported hearing the XE1FAS/b beacon on 28.171 MHz at 0542 UTC (12:42 AM local time) on August 26. “Just above the noise and then faded out,” he said. The path distance was 1,001 miles.

K6HPX has some fascinating antenna photos on his profile.

Here’s the latest video from Tamitha Skov, WX6SWW, the Space Weather Woman. You can always find her new videos here.

Sunspot numbers for August 19 – 25 were 25, 14, 25, 16, 14, 29, and 29, with a mean of 21.7. The 10.7-centimeter flux was 74.9, 77.7, 77.1, 77.1, 78.1, 80.9, and 83.6, with a mean of 78.5. Estimated planetary A indices were 4, 5, 3, 3, 4, 5, and 9, with a mean of 4.7. Middle latitude A index was 5, 6, 4, 4, 8, 5, and 8, with a mean of 5.7.

For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check out the propagation page of Carl, K9LA.

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.

Share your reports and observations.



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