Sunspot numbers drifted below 100 over the past week (May 14-20), and so the average daily sunspot number declined from 146.9 over the previous seven days to 92.1 in the recent period. Average daily solar flux dropped from 156.3 to 123.3.

You can see the decline in solar flux in addition to the decline in predicted numbers by downloading the spreadsheet at http://bit.ly/1KQGbRm, which shows us the daily readings and the shifting 45-day predictions from NOAA/USAF.

From that spreadsheet you can see that the predicted solar flux is 100 on May 22-28, 95 on May 24-28, 105 on May 29-30, 110 on May 31, 115 on June 1, 120 on June 2-3, 125 on June 4, 130 on June 5-6, 120 on June 7-12, 110, 115, 105 and 95 on June 13-16, 90 on June 17-19, 95 on June 20, and 105 on June 21-26. This value peaks again at 130 on July 2. ARRL Field Day is June 27-28, 2015 when predicted solar flux is 110 and 115, and predicted planetary A index is 5.

Predicted planetary A index is 5 on May 22-24, 8 on May 25-26, 5 on May 27-28, 8 on May 29-30, 5 on May 31 through June 1, 15 and 10 on June 2-3, 5 on June 4-6, 12 on June 7, 25 on June 8-9, 12 on June 10, 5 on June 11-12, then 8, 15 and 12 on June 13-15, and 5 on June 16-24. You can see these predicted values and more, going out 45 days, by downloading the spreadsheet at http://bit.ly/1IBXtnG .

OK1HH predicts geomagnetic activity will be quiet on May 22-23, mostly quiet May 24, quiet to active May 25, quiet May 26-27, quiet to unsettled May 28-29, mostly quiet May 30, quiet to unsettled May 31, mostly quiet June 1, active to disturbed June 2, quiet to active June 3, mostly quiet June 4-5, quiet to unsettled June 6, quiet to active June 7-9, disturbed June 10-11, mostly quiet June 12, quiet June 13, quiet to active June 14, active to disturbed June 15, quiet to active June 16, and quiet on June 17.

OK1HH says the reliability of his predictions are reduced (although I don’t know why) and that he sees a possible increase in solar wind on May 22-23, May 30, June 2-3, June 8-9 and June 12. He puts parenthesis around dates he is particularly uncertain about, and he has those around May 22-23 for both the quiet conditions prediction and the increase in solar wind. The two seem mutually exclusive to me, but since May 22-23 is today and tomorrow, we should know soon enough. He also has parenthesis around the increase in solar wind for June 8-9.

Jon Jones, N0JK, of Kansas shares this news about events on May 18: “An unexpected aurora event occurred May 18.

“Around 2245z aurora allowed stations in Minnesota, North Dakota, Illinois, Iowa, Michigan and southern Canada to make 6 meter contacts. I heard K9KU in Wisconsin and KC0CF in Iowa on 6 meter aurora in Kansas. The aurora was due to unsettled solar wind which sparked a G2-class geomagnetic storm.”


For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of the numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation. More good information and tutorials on propagation are at http://k9la.us/.

Archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format at http://bit.ly/1IBXtnG and http://bit.ly/1KQGbRm .

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 http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins.

Sunspot numbers for May 14 through 20 were 126, 113, 103, 75, 83, 84, and 61, with a mean of 92.1. 10.7 cm flux was 145.1, 136.5, 131, 119.6, 115, 110.3, and 105.6, with a mean of 123.3. Estimated planetary A indices were 10, 8, 6, 6, 16, 17, and 7, with a mean of 10. Estimated mid-latitude A indices were 9, 7, 7, 6, 15, 14, and 10, with a mean of 9.7.