SB PROP @ ARL $ARLP025 ARLP025 Propagation de K7RA ZCZC AP25 QST de W1AW Propagation Forecast Bulletin 25 ARLP025 From Tad Cook, K7RA Seattle, WA June 25, 2010 To all radio amateurs SB PROP ARL ARLP025 ARLP025 Propagation de K7RA Sunspot numbers were lower for the past week, compared to the previous period. Average daily sunspot numbers fell nearly 11 points to 16.1. 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 Propagation Forecast bulletins ARLP024 and ARLP023 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 one AU or Astronomical Unit, which is the average distance. ARLP023 mentioned an alleged increasing discrepancy between sunspots and solar flux, which seems apparent when you look at the information at http://www.solen.info/solar/ 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 in ARLP024, 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 at, http://tinyurl.com/ks8tvn. Just compare the observed values in the "fluxobsflux" column with the adjusted values in the "fluxadjflux" column. A note from Carl Luetzelschwab, K9LA points out that sunspot numbers and solar flux really don't correlated that well. On his web page http://mysite.ncnetwork.net/k9la/ click on the "Timely Topics" link and then the June 23 link, "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 at http://tinyurl.com/27nh6ky and toward the end of the piece is even some useful information about the state of the current cycle. If you would like to make a comment or have a tip for our readers, email the author at, k7ra@arrl.net. For more information concerning radio propagation, see the ARRL Technical Information Service web page 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. Find more good information and tutorials on propagation at, http://mysite.ncnetwork.net/k9la/index.html. 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 June 17 through 23 were 14, 16, 28, 13, 14, 14, and 14 with a mean of 16.1. 10.7 cm flux was 70.4, 70.5, 68.9, 70, 72, 73.3 and 74 with a mean of 71.3. Estimated planetary A indices were 10, 5, 4, 3, 5, 6 and 4 with a mean of 5.3. Estimated mid-latitude A indices were 8, 4, 2, 2, 6, 5 and 2 with a mean of 4.1. NNNN /EX