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The K7RA Solar Update


All daily sunspot numbers dipped into the double digits last week, with the average declining from 73.7 to 43.4. This compares the latest July 16-22 period against the previous seven days.

Over the same periods, average daily solar flux went from 114.8 to 95.1.

Geomagnetic indices were mostly quiet, with average daily planetary A index going from 13.7 to 6.1 and average mid-latitude A index declining from 12.3 to 8.1.

At 0749 UTC on July 23 the Australian Space Forecast Center posted a geomagnetic disturbance warning: “A sustained period of southward IMF is resulting in mildly elevated levels of geomagnetic activity, particularly at high latitude regions. Further mildly elevated levels of geomagnetic activity are possible during the remainder of 23 July.”

And indeed the planetary A index for the day was 23, with planetary K index reaching 3, 4, 5 and 3 over the first four 3-hour readings. The high latitude college A index was 33, with the first K index readings at 3, 4, 7, and 4.

Predicted solar flux is 90 on July 24, 95 on July 25, 100 on July 26-27, 105 on July 28-30, 110 on July 31, 115 on August 1-4, 110 and 105 on August 5-6, 100 on August 7-9, then 95 on August 10-13, finally dipping to 85 by August 15, then peaking (weakly) at 115 on August 28-31.

Predicted planetary A index is 15, 12, 8 and 5 on July 24-27, then 10, 8, 5 and 18 on July 28-31, then 25 and 12 on August 1-2, 5 on August 3-5, then 20, 25, 15, 10, and 8 on August 6-10, 5 on August 11-15, 10 on August 16, 5 on August 17-18, then 15 and 10 on August 19-20, 5 on August 21-26, then 18, 25 and 12 on August 27-29.

NOAA says the geomagnetic field is expected to be quiet to active on July 24-25 and quiet to unsettled on July 26.

OK1HH sees the geomagnetic field as quiet to active on July 24, quiet to unsettled July 25, mostly quiet July 26, quiet July 27, mostly quiet July 28, quiet July 29, quiet to active July 30, active to disturbed July 31 through August 1, quiet to active August 2, mostly quiet August 3, quiet on August 4, mostly quiet August 5, quiet to active August 6, active to disturbed August 7-8, quiet to active August 9, quiet to unsettled August 10, mostly quiet August 11, quiet August 12-14, mostly quiet August 15, quiet to unsettled August 16, mostly quiet August 17 and quiet on August 18.

He sees increases in solar wind on July 24-26, August 1-5, and 8-10. He sees uncertainty though for any predictions on July 26, August 1-5, August 8, August 17 and 18.

Here is an interesting article about how the far side views of the Sun from the STEREO mission are disrupted because the satellite transmissions back to Earth are blocked by the Ssun. But here the Curiosity rover on Mars fills in.

Check this table of predicted International Sunspot Numbers:


Note the next minimum is predicted roughly for July 2019, just four years from now, and unlike the last minima, there is some sunspot activity!  Let’s hope this is correct. Compare those numbers with all of 2009 in the same table. These are smoothed sunspot numbers, and someone out there is optimistic.

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

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 IE.

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 July 16 through 22 were 55, 40, 52, 46, 39, 37, and 35, with a mean of 43.4. 10.7 cm flux was 99.6, 97.4, 96, 99.4, 93.2, 91, and 89, with a mean of 95.1. Estimated planetary A indices were 8, 5, 4, 3, 5, 10, and 8, with a mean of 6.1. Estimated mid-latitude A indices were 15, 7, 4, 3, 7, 12, and 9, with a mean of 8.1.




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