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The K7RA Solar Update


Solar activity increased somewhat over this week’s reporting period, July 30 through August 5, compared to the previous seven days.

Average daily sunspot numbers increased from 47.9 to 70.3, while average daily solar flux was up from 96.4 to 104.5. Average daily mid-latitude and planetary A index remained about the same, both around 10.

At 2348 UTC on August 5, Australia’s Space Weather Services issued a geomagnetic disturbance warning. A high speed stream of solar wind from a coronal hole is expected to cause unsettled to active conditions with possibility of magnetic storms over high latitude regions on August 7, then settling down to stable conditions by late August 8.

Earth is entering the debris field from Comet Swift-Tuttle, and the resulting Perseid meteor shower should peak August 12-13. This offers the possibility of VHF meteor scatter communication on 6 and 2 meters, and possible enhancement of the ionosphere for upper HF bands as well.

Predicted solar flux for the near term is 115 on August 7, 120 on August 8-9, 115 on August 10-11, 110 on August 12-13, 90 on August 14-15, 95 on August 16-19, 90 on August 20-21, 95 on August 22-23, 100 on August 24-25, 105 on August 26-28 and 100 on August 29 through September 2.

Predicted planetary A index is 23, 15 and 24 on August 7-9, then 20, 12 and 8 on August 10-12, then 5 on August 13-17, then 12, 10, 8 and 12 on August 18-21, then 10, 5 and 8 on August 22-24, 5 on August 25-26, then 12, 18, 25, 12 and 10 on August 27-31, then 8, 5, 12, 18 and 8 on September 1-5, and 5 on September 6-13.

OK1MGW predicts geomagnetic activity will be active to disturbed August 7-8, quiet to active August 9, quiet to unsettled August 10-11, mostly quiet August 12-13, quiet on August 14-15, quiet to unsettled August 16-17, quiet to active August 18, quiet to unsettled August 19-22, mostly quiet August 23, quiet to unsettled August 24, quiet to active August 25-26, active to disturbed August 27, quiet August 28, quiet to unsettled August 29-30, mostly quiet August 31 through September 1, and quiet to active September 2.

OK1MGW expects increases in solar wind on August 7-9 and 25-28.

Average daily sunspot numbers for July 2015 were 68.5. This is down from 77.4 in June and 83 in May.

For our three-month moving averages, the peak for the current cycle was in 2014, when the averages centered on February and March were 146.4 and 148.2. The three-month moving averages for the remainder of 2014 were all above 100. The averages centered on January through June 2015 were 98.2, 78.1, 68.2, 72.4, 77.7, and 76.3. So the last figure, centered on June averages all the daily sunspot numbers from May 1 through July 31.

We had no reports from readers, except K7HV in Seattle mentioned that he observes reliable paths to Europe on 20 meters after local sunset.

David Jennings, N2EIO, of Ladys Island, South Carolina (between Charleston and Savannah, Georgia) asked about how to use the numbers we report in this bulletin, and how they affect propagation from his location. At the bottom of this bulletin are some resources, including a link to the K9LA web site. From there you can download W6ELprop for doing your own predictions from your location. For example, if we see that the predicted solar flux is around 110, W6ELprop says from his location at 32.44 degrees north, 80.64 degrees west a path to Hungary for today on 20 meters would be best around 2100-0100 UTC, with another possible opening around 0430-0530 UTC. 40 meters would be best around 0000 UTC to 0500 UTC. Checking paths to Costa Rica, 40 meters should be open all day and night, with strongest signals from 0030-1030 UTC, and 20 meters having the best path at 2130-0700 UTC.

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 July 30 through August 5 were 83, 71, 70, 51, 62, 68, and 87, with a mean of 70.3. 10.7 cm flux was 102, 100.7, 102.9, 101.5, 105.6, 106.8, and 112.2, with a mean of 104.5. Estimated planetary A indices were 12, 14, 10, 11, 6, 7, and 6, with a mean of 9.4. Estimated mid-latitude A indices were 12, 16, 9, 13, 9, 9, and 7, with a mean of 10.7.