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The K7RA Solar Update


Solar activity strengthened during the past week. Average daily sunspot numbers increased from 34.3 to 112.4, and average daily solar flux rose from 97.8 to 131.4. The middle latitude A index for June 10-11 can only be guessed, due to some sort of outage depriving us of K-index data over a 27 hour period. The outage began sometime after 1200 UTC June 9 and ended sometime before 1800 UTC June 10.

June 8 was the day with the most geomagnetic upset, when the planetary A index rose to 33.

Predicted planetary A index for the near term is 20, 15 and 16 on June 12-14, then 10, 8 and 6 on June 15-17, then 5 on June 18 through July 3. We then see another active period on July 4-9 when the predicted A index is 8, 20, 28, 20, 10 and 8, followed by 6, 5 and 8 on July 10-12, and 5 on July 13 and beyond.

At 0202 UTC on June 10 the Australian Space Forecast Centre predicted increased geomagnetic activity on June 12 due to a coronal mass ejection.

They issued a second warning at 0336 UTC predicting a glancing blow at earth early in the UTC day on June 12.

Predicted solar flux for the near term is 140 on June 12-13, then 135, 130, 125, 120 and 115 on June 14-18, 120 on June 19-26, 115 on June 27, and 120 on June 28-29. The forecast then shows solar flux rising to 145 on July 5-7 before settling back to 120 after July 12.

Petr Kolman, OK1MGW, of the Czech Propagation Interest Group gives us a geomagnetic forecast this week. He expects mostly quiet conditions on June 12, quiet on June 13, active to disturbed on June 14, quiet to active June 15-16, quiet June 17-21, quiet to unsettled June 22-25, quiet to active June 26-27, quiet on June 28-30, mostly quiet July 1-2, quiet to unsettled July 3, active to disturbed July 4, quiet to active July 5, and quiet to unsettled July 6-8.

He expects an increase in solar wind on June 14-15 and July 4-5.

OK1MGW has been writing these weekly forecasts with OK1HH since 1978.

David P. Moore sent us a link to an article titled “New Tool Could Predict Large Solar Storms More Than 24-hours in Advance.”

There were no reports from readers this week.

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 the file format.

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 June 4 through June 10 were 80, 105, 129, 136, 122, 110, and 105, with a mean of 112.4. 10.7 cm flux was 118, 126, 132.7, 137.3, 134.2, 136.5, and 131.4, with a mean of 131.4. Estimated planetary A indices were 3, 3, 5, 7, 33, 13, and 12, with a mean of 10.9. Estimated mid-latitude A indices were 4, 4, 7, 8, 22, 12, and 11, with a mean of 9.7.




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