SB PROP @ ARL $ARLP038<br />ARLP038 Propagation de K7RA<br /><br />ZCZC AP38<br />QST de W1AW <br />Propagation Forecast Bulletin 38 ARLP038<br />>From Tad Cook, K7RA<br />Seattle, WA September 9, 2005<br />To all radio amateurs <br /><br />SB PROP ARL ARLP038<br />ARLP038 Propagation de K7RA<br /><br />Last weekend began with a high speed solar wind provoking<br />geomagnetic instability, hence the high A index values. Conditions<br />quieted down after Sunday, but then sunspot 798 returned, which we<br />last saw in August. The spot released several powerful X-class solar<br />flares over the past couple of days, and although not squarely<br />pointed at Earth, glancing blows could cause greater geomagnetic<br />activity.<br /><br />Currently the interplanetary magnetic field points north, which<br />could offer some protection. The forecast for the planetary A index<br />for Friday through Monday, September 9-12 is 25, 20, 10 and 20.<br />Predicted solar flux for the same days is 100 for Friday, September<br />9, then values around 110 for the following week. A little higher<br />sunspot activity is welcome for the next couple of weeks, as we head<br />toward the Autumnal Equinox, usually a better time for HF<br />propagation.<br /><br />Randy Crews, W7TJ, asked about sunspot and solar flux numbers at the<br />bottom of the solar cycle, which is expected around the end of 2006,<br />or early 2007. Of course, there is enough daily variation that we<br />won't really know when the bottom was until well after it has<br />passed. We only know this for sure when looking at a smoothed curve<br />where daily numbers are averaged over many months.<br /><br />Of course we will see many days, sometimes weeks, with no sunspots<br />at all. Solar flux drops below 70 to a background level, around 67.<br />A typical low period was September and October 1996, in which the<br />average sunspot number was 2.6, and average solar flux was 69.3.<br />Perhaps we'll see these low numbers again about 12-18 months from<br />now.<br /><br />If you would like to comment or have a tip, email the author at,<br />k7ra@arrl.net.<br /><br />For more information concerning radio propagation and an explanation<br />of the numbers used in this bulletin see the ARRL Technical<br />Information Service propagation page at,<br />http://www.arrl.org/tis/info/propagation.html. An archive of past<br />bulletins is found at, http://www.arrl.org/w1aw/prop/.<br /><br />Sunspot numbers for September 1 through 7 were 24, 28, 14, 12, 12,<br />12 and 11 with a mean of 16.1. 10.7 cm flux was 79.2, 77.1, 74.2,<br />74.6, 75, 83.4, and 117, with a mean of 82.9. Estimated planetary A<br />indices were 21, 33, 32, 26, 14, 9 and 15 with a mean of 21.4.<br />Estimated mid-latitude A indices were 11, 24, 20, 18, 9, 6 and 18,<br />with a mean of 15.1.<br />NNNN<br />/EX

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