The K7RA Solar Update

SEATTLE, WA, Oct 17, 2003--Solar flux and sunspot numbers were lower this week, but the planetary A index was higher. In general, we like to see the reverse for favorable 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. 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 licensee in Richmond, Virginia, wrote to ask if 10 meters ever would open again. Expect to see less and less 10-meter propagation as the current cycle declines. While it's true that 10 meters can and does open even during the low points of the sunspot cycle, often on those occasions there is so little activity in that part of the spectrum that nobody notices.

We can run some numbers to see what KC4AQT is up against. From his license address, it looks like his coordinates are about 37.5 degrees north latitude and 77.5 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.

Plotting from his location in Richmond to mine in Seattle for October 16, it shows no openings at all on 10 or 12 meters and a remote chance of an opening on 15 meters from 1900 to 2100 UTC. That's early afternoon on the Seattle end. If KC4AQT upgrades, we'd have a pretty good chance of being able to contact each other on 17 meters, and an even greater opportunity on 20!

Let's compare that with conditions just one year ago. We can look at the sunspot numbers in old bulletins 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 until 0030 UTC. Twelve meters was open longer than that, and 15 was open from 1330 to 0230 UTC. If KC4AQT (and others in his situation) can upgrade, and if he has room for a larger antenna, 160, 80 or 40 meters may be more to his liking over the next few years--especially on those proverbial "long winter nights."

Over the next few days, sunspot numbers and solar flux should rise, 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, our friend in Richmond could see some 10-meter openings. However, as days get shorter, the northern hemisphere sees less sunlight, and we are farther from the peak propagation around the equinox.

Last week's bulletin mentioned solar activity forecasts by OK1HH. Franta informs that they are available weekly via the Web. When you check that Web page, note the dates are in the format such as 031017. We in North America would express that 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.

Sunspot numbers for October 9 through 15 were 68, 79, 77, 35, 25, 24 and 29, with a mean of 48.1. The 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.

Amateur solar observer Tad Cook, K7RA, Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday and an abbreviated version also appears in The ARRL Letter. Readers may contact the author via k7ra@arrl.net.

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