ARLP043 Propagation de K7RA:
October 22, 2004

Propagation Forecast Bulletin 43 ARLP043
From Tad Cook, K7RA
Seattle, WA October 22, 2004
To all radio amateurs

ARLP043 Propagation de K7RA

Solar activity made a comeback this week. Today's sun shows a string of spots all across the solar disk. Average daily sunspot numbers from last week to this week rose nearly 45 points, and solar flux was up over 6. This bulletin was written late Thursday night West Coast time (around 0700z) and the solar flux Wednesday (October 20) was 111, Thursday it was 112 and later today (Friday) through Sunday it is predicted to be 115, 120 and 115. Funny how less than two weeks ago the sunspot count was 0 for two days running, and on October 20 the sunspot number was 129.

Doug Bender, WW6D of Santa Rosa, California sent an interesting article from NASA outlining the significance of the sun's two spotless days. Like our bulletin last week (ARLP042), it reports that one has to look back to early 1998 to find a day with no sunspots prior to January of this year. The article quotes a solar physicist who says that this behavior is a sign that the solar minimum is coming. He notes that solar cycles are not exactly 11 years long, but have been as short as 9 years, with the longest running 14 years.

Of course we don't know the length of the cycle until some time after it is over, because there is enough daily variation that nobody can tell for sure when the maximum or the minimum occurred until a smoothed running average can be observed. As we've mentioned in previous bulletins, this article places the next solar minimum in late 2006. The article describes a theory that places a prediction for solar minimum about 34 months after the first spotless day following the peak of a solar cycle. David Hathaway, the scientist quoted in the article thinks the solar maximum will come about four years after the minimum, so expect that in 2010.

This is important to hams, of course, because averaging over a decade each, one doesn't get to experience many solar cycles in one's lifetime, unless you start young. In my case, I started out as WN7CSK, a 12 year old Novice almost 40 years ago near the minimum between Cycle 19 and Cycle 20. But at 52, how many more will I see? Cycle 19, the best sunspot cycle ever, peaked when I was about six years old and hadn't been introduced to ham radio, and it is unlikely I will ever see one as fantastic as Cycle 19.

Check out the article yourself at,

You can read some articles on solar cycle prediction at, and

Wes Wysocki, SP2DX wrote to comment on the recent bulletins, which mentioned the need to activate bands which are actually open, but seem dead due to lack of activity. He said for over a quarter century he has made it a habit to call on empty bands, and he usually gets some kind of reply. Recently he has been doing this on 17 and 12 meters, and half the time he scares up something at a considerable distance.

If you would like to comment or have a tip, email the author at,

For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page at,

Sunspot numbers for October 14 through 20 were 38, 26, 43, 51, 86, 86 and 129 with a mean of 65.6. 10.7 cm flux was 90.7, 89.2, 91.7, 91.9, 96.2, 99.1 and 111.3, with a mean of 95.7. Estimated planetary A indices were 27, 9, 5, 3, 4, 4 and 12, with a mean of 9.1. Estimated mid-latitude A indices were 12, 6, 3, 0, 4, 3 and 9, with a mean of 5.3.