The K7RA Solar Update


We soon may be talking about a day or two without sunspots as the norm, perhaps when looking at a preceding month -- quite the opposite of noting the few days with sunspots. It seems like a long time ago because of the long strings of spotless days. We saw eight days in a row with visible sunspots around mid-October, followed by another eight days around the start of November, then after just three days of no spots. By the end of today -- Friday, November 14 -- we may see five straight days, possibly followed by more.

Sunspot numbers for November 6-12 were 11, 0, 0, 0, 16, 18 and 21 with a mean of 9.4. The 10.7 cm flux was 68.6, 67.8, 68.3, 68.4, 69.3, 71.4 and 70.9 with a mean of 69.2. The estimated planetary A indices were 1, 8, 14, 12, 3, 1 and 2 with a mean of 5.9. The estimated mid-latitude A indices were 0, 7, 11, 10, 3, 1 and 4 with a mean of 5.1.

We have to look at last year to find long periods without spotless days. From June 25, 2007 until July 19, 2007, there were 25 days with sunspots that were continuously visible. From April 25, 2007 until May 23, 2007, there were 29 days with spots; from December 30, 2006 until February 10, 2007, there were 43 days with spots. This makes January 2007 the last time we observed a calendar month with no spotless days.

Why are sunspots important? They correlate with a reflective or refracting ionosphere. The University of Iowa has a nice picture illustrating the how the Earth's ionosphere works. Another illustration -- this one from Ray Heffer, G4NSJ -- shows a shortwave radio signal travelling a great distance via the ionosphere.

There are variations influenced by time of day, season and location, but generally the higher the sunspot number, the higher the frequency that can be used for communication. This is important, because when you double the frequency you are operating on (for instance, from 20 to 10 meters), the relative size of your antenna can be cut in half to still have the same efficiency. So, with enough solar activity, you could communicate around the world on 10 meters (28 MHz) with a highly efficient directional antenna that is much smaller and easier to construct than an equally efficient 20 meter (14 MHz) antenna. At the higher frequencies, there is also less absorption of higher frequency shortwave signals.

There is a critical number called the Maximum Usable Frequency (MUF). This number is be calculated based on the factors mentioned above: time of day, time of the year, the two locations trying to communicate and the level of solar activity. Radio waves at a frequency above the MUF just pass on through the ionosphere, never to be heard again. For calculating conditions based on these factors, check the reference to the same W6ELprop program mentioned in the last week's bulletin last week.

The ARRL SSB Sweepstakes Contest is this weekend. With the recent sunspot activity, conditions should be better on 15 meters than they would be without sunspots. For example: California to Ohio. If there had been no sunspots leading up to the contest weekend, 15 meters looks rough, but could open from 1800-1930 UTC, perhaps as early as 1600 to as late as 2100 UTC. But with recent sunspots, a great opening from 1630-2100 UTC is likely and could start an hour earlier and end 30 minutes to an hour later.

With no sunspots over that path this weekend, the MUF would rise above 20 MHz 1730-2000 UTC, peaking around 20.6 MHz at 1830 UTC. But with sunspots over a few days, the MUF is likely to go above 21 MHz from 1630-2100 UTC, peaking at 23.7 MHz around 1830 UTC.

On 20 meters with no sunspots, the path looks good 1430-1530 UTCand 1800-1830 UTC. With sunspots, 20 meters looks good 1430-1500 UTC, and excellent 1600-2000 UTC. Forty meters is good over the path day and night, sunspots or no. Strongest signals are from when the Sun sets around 0047 UTC in California to within the hour after the sun rises in Ohio around 1219 UTC.

Jeff Hartley, N8II, of Shepherdstown, West Virginia, wrote to us last week about the phone weekend of the CQ Worldwide DX Contest, October 25-26: "I operated the CQWW single band on 15 meters and the band was poor compared to most years, probably about the same as in 2007. The skip zone was long enough that I didn't work several active northern Caribbean countries until mid-afternoon Sunday. There appeared to be sporadic-E to VE1/VY2 and VE3 Saturday morning, and to VP5/VP9/C6 on Sunday. The closest F2 contact to my south was KP2M. There was decent propagation to very southern EU both days. I caught VU7SJ (loud) about the same time as the Es around 1400 UTC Saturday and VU2PAI (weak) called in Sunday around 1600 UTC for my best polar opening DX. It was possible to work about 30 zones on 15 meters from the USA. From 1245-1355 UTC Sunday, there was a big opening with S9+ EU signals about as far as Lithuania. I worked three Russians in UA3 and UA6 and one UR. On Sunday afternoon, 5R8FU was loud with a huge pile-up; all of Africa was workable, but zones 34 (missed), 36, 37 and 39 were pretty rare. Best Pacific DX was AH0 around 23 UTC Sunday. "Forty and 30 meters seem to be staying open to EU quite late some days which is encouraging."

Owen Duffy, VK1OD, of Ainslie, near Canberra in Southeast Australia, sent in a link to a chart he made of spotless days around the solar cycle transition. Check out the rest of his site, too.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.