The K7RA Solar Update


Finally! A sunspot group appeared this week, about three weeks since the last group disappeared. The first spotless day after sunspot group 1008's last appearance was Tuesday, November 18; the last spotless day before group 1009 emerged was Tuesday, December 9. As expected, this was another Solar Cycle 24 group, emerging far south of our Sun's equator.

Sunspot numbers for December 4-10 were 0, 0, 0, 0, 0, 0 and 13 with a mean of 1.9. The 10.7 cm flux was 69.6, 68.8, 69.1, 69, 68.5, 68.7 and 70.8 with a mean of 69.2. The estimated planetary A indices were 6, 10, 7, 6, 5, 0 and 2 with a mean of 5.1. The estimated mid-latitude A indices were 4, 7, 14, 6, 1, 1 and 2 with a mean of 5.

This weekend is the ARRL 10 Meter Contest. It would be great to have enough sunspots to drive the Maximum Usable Frequency (MUF) above 28 MHz, but that doesn't seem likely, as group 1009 is near the western limb of the visible solar disk.

What level of solar activity would we need in order to see the MUF above 28 MHz? That varies according to the locations of the two stations trying to communicate, the season and the time of day. For example, if the date is December 13, the path from Cleveland, Ohio to Dallas, Texas is likely to briefly have an MUF at 28.0 MHz around 1730 UTC, if the average sunspot number was at least 105 for several days. In our example, if the average sunspot number for several days was 125, the 3 hour period from 1700-2000 UTC would have an MUF above 28 MHz, and the 1730-1800 UTC period would likely have the best signals. If we calculate the path from Boston to Atlanta for the same date, the average sunspot number for several days should be at least 131 -- instead of 105 -- to reach an MUF of 28.0 MHz.

But don't expect 10 meters to be unusable this weekend. An MUF above 28 MHz is desirable for very reliable communications, but perhaps Sporadic-E will offer surprises. Summer Sporadic-E is more intense, but this time of year we should see at least some Sporadic-E.

A few weeks ago, Vic Woodling, WB4SLM, of Centerville, Georgia, wrote about an experience on 30 meters in the middle of the day, copying strong European stations and also 5R8IC working into Europe from Madagascar, but with weaker signals on Vic's end. This was at 1630 UTC, and when Vic came back to the radio at 1830 UTC, they were even stronger. Although in Vic's experience this is uncommon, a check with a propagation program for 30 meters on November 22 with zero sunspots between Georgia and England shows propagation closely matching his report. At 1630 UTC, it shows the relative signal level at 15 dB, and then at 1830 UTC it jumps to 29 dB. But if he looks further east to the Czech Republic, the signals stay around the level that they would be for England at 1630 UTC, all through the same period.

Ed Clulow, N7TL, of Portland, Oregon, commented on 75 meter conditions during the ARRL November Sweepstakes (Phone) that was November 15-17; he uses an inverted-V dipole. He said that after dabbling in contests for several decades, he had never seen propagation like it was on Saturday evening, saying it sounded more like 20 meters. He worked Midwest and East Coast stations with ease, snagging them on the first or second call. He knows some hams never venture below 20 meters, and thinks some of us may be missing good propagation at the bottom of the sunspot cycle.

Dave Bennett, VE7YJ, of Aldergrove, British Columbia, wrote, "Carrying on from WE0H's report on 600 meter activities, I have noted in the past week or so reception from the powerful Far Eastern Russian broadcasters on 153, 180, 189, 234 and 279 KHz. They were at their best on November 29, around 0700 UTC, but were heard as early as 0440 UTC. They haven't been as good the last couple of days, but were still detectable. I'm using an old IC-751A with a 160 meter inverted-V antenna and could probably get even better results with a bigger antenna. The last few nights, 160 meters has been spotty as well. VE6s were strong, but the Century Club Net on 1892 has been poor, whereas the week before I was hearing stations as far east and south as Texas and Ohio."

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.