ARLP042 Propagation de K7RA:
October 17, 2003

Propagation Forecast Bulletin 42 ARLP042
From Tad Cook, K7RA
Seattle, WA October 17, 2003
To all radio amateurs

ARLP042 Propagation de K7RA

Solar flux and sunspot numbers were lower this week, and the planetary A index was higher. Generally we like to see the reverse for HF propagation. The planetary A index was low for October 9-12, but on October 14 and 15 conditions were quite stormy. This is because a coronal hole on the sun was spewing a strong solar wind, and the interplanetary magnetic field pointed south, leaving earth vulnerable. The planetary A index was 48 and 42 on October 14 and 15, and Alaska's high latitude college A index was 65 and 71.

When the sunspot count went to 24 on October 14, this was the lowest sunspot number since May 10 of this year, when it was 22. We should expect more days like this as the solar cycle declines.

Sam Coppedge, KC4AQT, a Technician class radio amateur in Richmond, Virginia wrote to ask if 10-meters would ever be open again at all. Expect to see less and less 10-meter propagation as time goes on. Even during the lower parts of the sunspot cycle 10-meters sometimes opens, but in those years there is so little activity in that part of the spectrum that nobody notices.

We can run some numbers to see what Sam is up against. From his license address, it looks like he has coordinates of 37.4862 degrees north latitude and 77.4699 degrees west longitude. Using W6ELprop, we can use the average sunspot number from the past few days, October 12-16, which is 28. You can use the sunspot number in W6ELprop by entering S before the digits. If I plot from his home in Virginia to mine in Seattle for October 16, it shows no opening at all on 10 and 12-meters and a remote chance of an opening on 15- meters from 1900-2100z. This is early afternoon on the Seattle end. If Sam gets his General Class license, he'd have a pretty good bet to talk to me on 17-meters and a greater opportunity on 20-meters.

Now let us compare that with a year ago. We can look at the sunspot numbers in old bulletins by checking the web site or check the data list in WA4TTK's solar plotting utility. It shows sunspots for the same five-day period leading to October 16, 2002 yielding an average number of 172. Plug that number into the same program, and the results are vastly different.

This is instructive, because the seasonal effects are identical. Last year at this time 10-meters should have opened solid with strong signals from morning until evening Seattle time, from 1500-0030z. 12-meters was open longer than that, and 15-meters was open from 1330-0230z. If Sam can upgrade and has room for a longer wavelength antenna, 160, 80 or 40-meters may be more to his liking over the next few years, especially on long winter nights.

Over the next few days, we should see sunspot numbers and solar flux rising, with solar flux values peaking around October 25 at 130. Solar wind over the next few days should cause more geomagnetic upset, with the October 17-22 planetary A index pegged at 25, 20, 15, 15, 30 and 25.

If solar flux and sunspot numbers rise as predicted over the next week, Sam could see some 10-meter openings. However, as days get shorter, the northern hemisphere is seeing less sunlight and we are further from the peak propagation around the equinox.

In last week's bulletin, solar activity forecasts by OK1HH were mentioned. Franta wrote to tell us they are available weekly on the web at When you check that web page, note the dates are in the format of 031017 for what most folks in North America would express as 10-17-03.

For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at Email the author of this bulletin at,

Sunspot numbers for October 9 through 15 were 68, 79, 77, 35, 25, 24 and 29, with a mean of 48.1. 10.7 cm flux was 110.8, 111.8, 105.8, 97.8, 94.4, 92.4 and 95.9, with a mean of 101.3. Estimated planetary A indices were 8, 5, 5, 6, 13, 48 and 42, with a mean of 18.2.