Fall 2004 Issue

PROPAGATION

The Cold Facts

Solar Cycle 23 is moving steadily toward the years of minimum activity, predicted to be toward the end of 2006 and the beginning of 2007. The monthly smoothed sunspot counts for each month in this period are expected to be between 28 and 23. Compare that with last year’s 57 to 52, and 2002’s 85 to 81. The resulting solar activity, as measured in the 10.7-cm flux, is quite a bit less this year than the last few years. Under such lowered activity levels, will there be much F2 VHF propagation this season? Without the supporting energizing influence of a moderate to highly active sun, with 10.7-cm flux readings above 200, it is unlikely that we’ll see significant VHF long-range DX via F2 propagation.

Autumn (November through January) is also not known to be typical transequatorial propagation (TEP) season. TEP, which tends to occur most often during spring and fall, requires high solar activity, energizing the ionosphere enough to cause the F-layer over the equatorial region to support VHF propagation. The normal TEP signal path is between locations on each side of the equator. However, without the level of solar activity needed to keep the F-layer energized enough for VHF propagation, these paths don’t materialize. The fall season of TEP usually tapers out by mid-November. This year, though, TEP is not a major player.

What could become an exciting mode of propagation this season is sporadic-E. This summer’s sporadic-E season was one of the best on record, surprising many VHF veterans, some of whom claim that this summer’s Es was the best since the 1960s.
 

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Aurora over the SuperDARN TIGER site in Tasmania, operated by the La Trobe University in Australia. (Composite image courtesy of photographer Danny Ratcliffe and the TIGER Consortium; source: National Science Foundation)