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The K7RA Solar Update


Sunspot numbers were lower for the past week, compared to the previous period. The average daily sunspot numbers fell nearly 11 points to 16.1. Sunspot numbers for June 17-23 were 14, 16, 28, 13, 14, 14 and 14, with a mean of 16.1. The 10.7 cm flux was 70.4, 70.5, 68.9, 70, 72, 73.3 and 74, with a mean of 71.3. The estimated planetary A indices were 10, 5, 4, 3, 5, 6 and 4, with a mean of 5.3. The estimated mid-latitude A indices were 8, 4, 2, 2, 6, 5 and 2, with a mean of 4.1.

ARRL Field Day is this weekend, and it looks like we could have unsettled to active geomagnetic conditions. NOAA predicts solar flux for June 25-27 at 75, 75 and 76, and planetary A index at 8, 15 and 12. Beyond that, the predicted solar flux for June 28 through July 1 is 76, 77, 77 and 72, with planetary A index of 10, 10, 12 and 15. Geophysical Institute Prague calls for unsettled conditions June 25, unsettled to active June 26, unsettled June 27-28, quiet to unsettled June 29 and unsettled June 30 and July 1.

The predicted solar flux for this weekend is slightly higher than it has been this week. In fact, solar flux has been below the 75-76 range since June 11-13. Of course, we want solar flux and sunspot numbers to be high, with geomagnetic indices such as planetary A index to be low.

In last week’s bulletin and the week before, we talked about solar flux, both observed and adjusted. The adjusted values are based on what the measurements would be if the distance from Earth to Sun were at 1 AU (Astronomical Unit), the average distance.

In the bulletin from two weeks ago, we mentioned an alleged increasing discrepancy between sunspots and solar flux, which seems apparent when you look here and see the gradually declining solar flux. But actually this is probably due to the changing distance between Earth and Sun, since these are observed numbers, not adjusted.

As noted last week, the observed values would be adjusted down in January and up recently to get the adjusted values, and this would probably yield a more constant value in the chart in the previous paragraph. If you want, you could chart it out yourself using the numbers here. Just compare the observed values in the “fluxobsflux” column with the adjusted values in the “fluxadjflux” column.

A note from K9LA, Carl Luetzelschwab points out that sunspot numbers and solar flux really don’t correlated that well. Go to Carl’s site and click on the Timely Topics link and then the June 23 link called “The Variability of the Sun.” Carl’s Web page has a great deal of good information explaining propagation concepts.

MSNBC has an interesting article about sunspots in popular culture; toward the end of the piece is even some useful information about the state of the current cycle.


All times listed are UTC, unless otherwise noted.


Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.




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