The K7RA Solar Update
The recent sunspot activity that we've been experiencing remains strong. The weekly averages of daily sunspot numbers that we've been reporting over the past six weeks were 1.9, 21.1, 31.4, 21.9, 14.6 -- and now 26.4. Sunspot region 1035 re-emerged as region 1040 on January 7 and has been growing steadily. For January 7-14, the total area of region 1040, as expressed in millionths of a solar hemisphere, was 80, 40, 70, 130, 300, 300, 380 and 290. It passed the 0 degree meridian (the imaginary vertical line on the visible Sun that faces straight toward Earth) and now looks like it has another four days before it crosses the Sun's western horizon; you can see this on the STEREO Web site. A bright area that may be a sunspot is slipping out of the dark area, the approximately 12.8 percent of the Sun unseen by the STEREO craft. This may reach our Sun's eastern horizon just after region 1040 passes over the western horizon.
Sunspot numbers for January 7-13 were 15, 14, 20, 25, 35, 35 and 41 with a mean of 26.4. The 10.7 cm flux was 78.1, 77.4, 81.7, 84.4, 89.2, 93.3 and 90.5, with a mean of 84.9. The estimated planetary A indices were 1, 2, 1, 2, 6, 3 and 6, with a mean of 3. The estimated mid-latitude A indices were 0, 0, 1, 2, 4, 2 and 4 with a mean of 1.9.
Ed McKie, KB5GT, of Yazoo City, Mississippi, wrote to ask how high the solar flux has to go before he starts noticing a big difference in HF propagation. He wondered if we could use 20 meters as an example. I told Ed that I have heard that flux is a good relative indicator related to sunspot activity, but I've also been told that the popular prediction software is best used with sunspot numbers. The algorithms are based on the predicted smoothed sunspot number, which of course is an average going six months back and six months into the future, so half of it is a guess. The programs are a statistical guess based on the conditions being at least as good as predicted half the time and less than that the other half, based on that smoothed number. You can find the latest predicted smoothed sunspot numbers here.
Another source is the Preliminary Report and Forecast of Solar Geophysical Data from the NOAA Space Weather Prediction Center. Usually, the first issue of any new month will give a new table of predictions, along with a graph. The recent issue, #1792, has the information on page 9.
One approach would be to make a rough estimate, month by month as the smoothed sunspot number increases, to specific locations from your QTH, using W6ELprop. There is a good introduction to using W6ELprop on Carl Luetzelschwab's, K9LA, Web site: Just click on "Tutorials," then "Downloading and Using W6ELprop."
KB5GT is located at 32.867 degrees north latitude, 90.367 degrees west longitude. Let's try a prediction from his location to Spain, for mid-February, with the predicted smoothed sunspot number of 17.4 and look at 20 meters. On February 15 using 14.1 MHz, we see the A and B rated (meaning good probability of a path) period runs from 1630-2000 UTC, with relative signals at 25-28 dB above a half microvolt. On March 15 and a smoothed sunspot level of 20.2, the A-rated opening starts an hour earlier at 1530 UTC, but 4 dB lower than the previous month; from 1800-1830 UTC, it drops about 8 dB. The B-rated period ends at 2200 UTC. So the opening should last longer, but with lower signal levels than February. The following month using 23 for the smoothed sunspot number, the opening starts slowly, with signal levels gradually improving until 0100 UTC.
You can see how this exercise gives one an appreciation for seasonal variations more than anything. Skipping ahead to September with a sunspot number of 37.1, we see another slowly improving opening, ending around 2330 UTC. Note also that the 17 meter conditions are quite good. In February, any 17 meter opening was predicted as very brief. Looking at November 15, 2010 and using a sunspot number of 42.5, the openings are short in the dark Northern Hemisphere. Go to September 2011with a sunspot number of 67.9, 20 meters is open longer. Note also the odd improvement in the odds at 0430 UTC.
So when has it improved? The improvement is gradual, and there aren't any rules for what is "good enough." As you learn about your station's capabilities, you will form your own opinion. But don't let the perfect be the enemy of the good. By all means, get on the air!
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 each Thursday 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.