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The K7RA Solar Update


This week the average daily sunspot number moved up from 66.9 for the September 10-16 period, to 73 for the next seven days. Average daily solar flux changed from 97.3 to 106.7. There was one new sunspot group on September 20, two more on September 22, and another new one on September 23.

At 0005 UTC on September 20 the Australian Space Forecast Centre issued a geomagnetic disturbance warning for September 20 and 21 due to a coronal mass ejection. Sure enough, at the end of the day on September 20 the planetary A index hit 43, which indicates possible aurora and a high level of absorption for HF signals.  The college A index (Fairbanks, Alaska) reached 73. reported the CME impact hit earth a day earlier than expected.

A second similar warning was issued at 2255 UTC on September 21 for the following day, but the CME missed, and had no impact. Conditions were quiet and stable.

NOAA has had some trouble of late getting the daily 45 day forecast of solar flux and planetary A index from the Air Force. This is because of some issues with moving to new servers.  Thanks to Robert Steenburgh, AD0IU, who is a space scientist at NOAA for keeping us up to date with missing data.

If you check for updated forecasts and ever have a problem with the links, you can check here for the latest numbers for the current day only:

or here:

The latest forecast (from September 24) has predicted solar flux at 110 on September 25-26, 105 on September 27, 110 on September 28, 105 on September 29-30, 100 on October 1, 95 on October 2-5, 100 on October 6-7, 105 on October 8-11, 100 on October 12, 95 on October 13-15, 90 on October 16-17, and 110 on October 18-20.

Predicted planetary A index is 15 on September 25-26, then 8 on September 27-30, 20 on October 1, 15 on October 2-3, then 45, 25 and 18 on October 4-6, 12, 50 and 15 on October 7-9, and 12 on October 10-16.

In addition to the high A index predictions for October 4 and 8 (45 and 50), 45 is predicted again for October 31 and 50 again on November 4.

Petr Kolman, OK1MGW, of the Czech Propagation Interest Group sends along his weekly forecast for geomagnetic activity: Quiet to unsettled conditions on September 25, quiet on September 26-28, mostly quiet September 29, quiet to unsettled September 30, quiet to active October 1-3, quiet to unsettled October 4-6, active to disturbed October 7-8, quiet to unsettled October 9-10, quiet to active October 11-14, quiet to unsettled October 15, quiet to active October 16-17, mostly quiet October 18-20, and quiet to unsettled on October 21. Petr also expects increases in solar wind on October 1-3, 7-10, and 16-17.

The Autumnal equinox was on Wednesday, September 23 at 0822 UTC. This is when the Northern Hemisphere moved into Fall, and the Southern Hemisphere saw spring. Right now, close to the equinox is a good time for HF propagation, particularly between the Northern and Southern Hemispheres.

Thanks to Frank Donovan, W3LPL, for alerting us to a new scientific paper in the Astrophysical Journal, “The Recent Rejuvenation of the Sun's Large-Scale Magnetic Field: A Clue for Understanding Past and Future Sunspot Cycles” showing evidence that perhaps solar cycle 25 won’t be weaker than the current Solar Cycle 24.



The paper begins: “The quiet nature of sunspot cycle 24 was disrupted during the second half of 2014 when the Sun's large-scale field underwent a sudden rejuvenation: the solar mean field reached its highest value since 1991, the interplanetary field strength doubled, and galactic cosmic rays showed their strongest 27-day modulation since neutron-monitor observations began in 1957; in the outer corona, the large increase of field strength was reflected by unprecedentedly large numbers of coronal loops collapsing inward along the heliospheric current sheet.”

Jon Pollock, K0ZN, of DeSoto, Kansas reports in an e-mail titled “Excellent 10 MHz Propagation”, “Sunday night (9/20/15) from 0300 to about 0330 UTC, 3B8CF (Mauritius Island, in the Indian Ocean) was quite strong into Eastern Kansas. That is a 10,400 mile path from my home. Obviously, I have no way of proving it, but due to the relative lack of fading on his signal, I suspect ionospheric ducting; not an uncommon event on 10 MHz from what I have seen. Thirty meters was extremely quiet that evening after about 0245 which probably led people to think it was ‘dead’, but I have heard this many times before. I could hear absolutely no state side stations east of here but I could hear 3B8CF responding to them giving good reports, again confirming how long the skip was. When the 30 meter band gets very quiet at night, it is usually very long skip to some part of the world.”

Check out K0ZN’s description of his antenna system on his biography.

Dick Bingham, W7WKR, of Stehekin, Washington is excited about 160 meters and WSPR mode. He sent this report a week ago: “One hundred and sixty meters seems to be perking up now. I was running 5 watts in WSPR-mode last week and had a nice report of being ‘heard’ by VK2KRR down under. Not bad for 5 watts. I will be trying JT9 software tonight. It is supposedly better on MF and 160-meters, by several dB, than WSPR and the JT65 modes other 160-meter folks are using.

“If you have not already tried some of the K1JT digital modes, I would suggest you at least try WSPR for a few days. I was very impressed after my first attempts using it and am now 'sold' on the mode. WSPR is a great way to see where you are being 'heard', and how well, in the days before a contest.

“The antenna I use on 160-meters is what is called a ‘Half-Square.’ It is a great antenna if you have tall trees or towers available. My H-S is supported at about 90-feet at both ends of an L/2 top-wire phasing section (basically a non-radiator). Two L/4 end wires connected to the top wire ends slope away toward 10-feet above ground where one end is fed using a Hi-Z tuner.  My H-S's Figure-8 pattern basically radiates E/W, so Australia is on the great-circle path and probably the reason I get into that part of the world, running 5 watts, so well.

“I have found this antenna highly desirable because it seems to work well without a ground more significant than an eight-foot ground rod pounded into my gravel/sand valley bottom where I live here at Stehekin. One hundred watts has gotten me into England, Germany and Sweden using CW and the H-S.

“You will be amazed at what you hear, and who hears you, after you load and run the WSPR software. Look for the WSPR4.00r4171.exe software as opposed to earlier versions.

“Those of us who are part of the ARRL 600-meter experiment (WD2XSH-##) find WSPR to be a useful tool for our propagation studies on 475.7KHz.

“The most modest of antennas will perform well for you. Once you run for a week or so, make some improvements in your antenna and then run another week to evaluate your improvements. Barring markedly different propagation conditions, you should be able see differences between antennas. Run 1 watt and be ready to be surprised to see how many stations will copy you!”

Here are some details on half-square antennas:

Here is information on WSPR:

For more information concerning radio propagation, see the ARRL Technical Information Service at For an explanation of the numbers used in this bulletin, see An archive of past propagation bulletins is at More good information and tutorials on propagation are at

My own archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format at and .

Click on “Download this file” to download the archive and ignore the security warning about file format. Pop-up blockers may suppress download. I’ve had better luck with Firefox than Internet Explorer.

Monthly propagation charts between four USA regions and twelve overseas locations are at

Instructions for starting or ending email distribution of ARRL bulletins are at

Sunspot numbers for September 17 through 23 were 72, 62, 61, 74, 68, 79, and 95, with a mean of 73. 10.7 cm flux was 106.8, 102.8, 105.7, 110.4, 103.4, 107, and 110.7, with a mean of 106.7. Estimated planetary A indices were 12, 13, 16, 43, 9, 10, and 14, with a mean of 16.7. Estimated mid-latitude A indices were 12, 11, 12, 32, 9, 8, and 13, with a mean of 13.9.




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