Spring 2008 Issue

A Broad Look at 6m F2 Propagation
for Cycle 24 and Beyond

Press releases in January told of the beginnings of solar Cycle 24. Now that it seems to have begun,
the next question is what the cycle will look like over the next few years. K9LA gives some insight
into what to expect for the new cycle.

By Carl Luetzelschwab, K9LA

Earlier this year, on January 4, Sunspot Region 981 rotated into view. It was at 30°N solar latitude, and it was of the opposite magnetic polarity compared to previous Northern Hemisphere sunspots of Cycle 23. Since sunspots at the end of Cycle 23 occur near the solar equator, and since this new sunspot was at high latitude and of the opposite magnetic polarity, it turned out to be the long-awaited first sunspot of Cycle 24.

What does Cycle 24 hold in store for 6-meter F2 propagation? From a prediction of the Cycle 24 magnitude, we can make a rough estimate of when to expect 6-meter F2. Unfortunately, there is no single consensus for the magnitude of Cycle 24. Of the many predictions in the scientific community (more than 30, and they range from very low to very high), the general consensus among scientists is that Cycle 24 will either be a larger than average cycle or a slightly smaller than average cycle. Figure 1 shows these two predictions from the Solar Cycle 24 Prediction Panel in terms of 10.7-cm solar flux, and adopted by the International Space Environment Service (from http://sec.noaa.gov/SolarCycle/). Note that the rate of ascent of Cycle 24 at the beginning of 2009 may give us an early indication of where Cycle 24 is headed.

The prediction for the larger than average cycle says a maximum smoothed 10.7-cm solar flux of around 185 will occur in late 2011. The prediction for the slightly smaller than average cycle says a maximum smoothed 10.7-cm solar flux of around 140 will occur in mid-2012.

From probabilities of 6-meter F2 propagation versus 10.7-cm solar flux (Emil Pocock, W3EP, “Predicting Transatlantic 50-MHz F-Layer Propagation,” QST, March 1993), we can estimate when we’re likely to see 6-meter F2 propagation during Cycle 24. The W3EP data indicates the first signs (low probability) of 6-meter F2 propagation may occur when the 10.7-cm solar flux is around 140, and 6-meter F2 propagation increases to a probability of 50% when the 10.7-cm solar flux is around 220. It should be noted that these flux values need to be concurrent with a fall, winter, or spring month for those of us in the Northern Hemisphere, as these months result in the highest daytime maximum usable frequencies.

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