SB PROP @ ARL $ARLP017 ARLP017 Propagation de K7RA ZCZC AP17 QST de W1AW Propagation Forecast Bulletin 17 ARLP017 From Tad Cook, K7RA Seattle, WA April 29, 2005 To all radio amateurs SB PROP ARL ARLP017 ARLP017 Propagation de K7RA Solar flux and sunspot numbers continue their lull, although again this week their relative positions see-sawed. For last week's bulletin of April 22 (ARLP016), we reported average daily sunspot numbers up a little, and average daily solar flux down a bit. This change was noted when the numbers were compared to the data in the April 15 bulletin (ARLP015). This week the daily sunspot number on average dropped 25 points to 25.9, and the average daily solar flux increased a little over two points to 84. Nothing significant about any of this, which is common behavior as the solar cycle continues to decline. This week on Sunday, April 24 the earth-facing sun was spotless, and the sunspot number was 0. But the next day a new sunspot appeared, number 756, and it is a big one. The spot is growing quickly, and the resulting sunspot numbers for April 26-28 were 20, 45 and 71. Solar flux is heading toward 100. Predicted solar flux values for this weekend, April 29-May 1 are 103 on all days. Flux values should rise above 105 by Monday, May 2. Geomagnetic conditions have been nice and quiet, but this could change over the next week. The predicted planetary A index for April 29 through May 3 is 8, 8, 20, 40 and 15. A planetary A index of 40 indicates a major geomagnetic storm, which is expected from the reappearance of a recurring coronal hole and associated high velocity wind stream. The predicted smoothed sunspot number drops in May from 22 to 19. It will continue to decline, with the predicted smoothed sunspot number at 10 for the end of 2005 and 5 for the end of 2006, the predicted bottom of the solar cycle. In 2007 solar activity should rebound, and around the end of that year the smoothed sunspot number should be back to where it is now, 18 for November and 21 for December 2007. In 2008, based on the behavior of past solar cycles, sunspots should make a strong return. That's only three years from now. Robert Wilson, AL7KK wrote to say he worked for Voice of America and planned medium wave AM broadcasts that were around the 160 meter wavelength. He said that in 1989 he was using some propagation software that worked fine on 160 meters outside of the auroral zone. I've asked him to give us more detail, as the propagation programs I've used don't work below 3 MHz. I hope to have more information soon. David Moore sent us a fascinating article from SpaceRef.com about the structure of coronal holes and the associated solar wind. The article talks about observations published in the April 22 edition of Science. You can read the SpaceRef article at http://www.spaceref.com/news/viewpr.html?pid=16721 . If you would like to comment or have a tip, email the author at, k7ra@arrl.net. For more information concerning radio propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page at, http://www.arrl.org/tis/info/propagation.html. An archive of past bulletins is found at http://www.arrl.org/w1aw/prop/ . Sunspot numbers for April 21 through 27 were 22, 34, 35, 0, 25, 20 and 45 with a mean of 25.9. 10.7 cm flux was 77.1, 77.2, 79.3, 82.3, 86, 90.9 and 95.3, with a mean of 84. Estimated planetary A indices were 4, 9, 6, 10, 11, 5 and 4 with a mean of 7. Estimated mid-latitude A indices were 2, 7, 5, 5, 9, 2 and 1, with a mean of 4.4. NNNN /EX