Fall 2005 Issue

Is the End of Cycle 23 Near?

 By Tomas Hood, NW7US/AAAØWA

Does solar Cycle 23 have enough life left to spark some excitement for those of us hunting for exotic VHF propagation? Also, what is the outlook for Cycle 24?

The current cycle has not been too exciting for VHF enthusiasts, with Cycle 23 peaking at a smoothed sunspot number of 120.8. That’s a bit dismal compared to previous cycles. Cycle 21 peaked at 164, and Cycle 22 peaked at 158. Compare these last three 11-year solar activity cycles to Cycle 19 from the late 1950s, which had a smoothed peak of 201.3. That’s a cycle remembered fondly among VHF veterans, with frequent worldwide F-layer openings on 6 meters and plenty of aurora-mode propagation.

The official prediction for the ending of the current solar cycle is around the end of 2006. This prediction has not been changed for several years and is thought to still be valid. However, a panel of scientists is planning to meet in early 2006 and hopes to provide an update in April 2006. I don’t expect the outlook to change too much, and I continue to postulate the end of Cycle 23 to occur in the fall of 2006.

Despite the impending death of Cycle 23 in about a year’s time, there have been recent moments of rather energetic bursts of solar activity. An example occurred during September, when a huge sunspot rounded the sun’s eastern limb. As soon as it appeared it exploded, producing one of the brightest x-ray solar flares so far recorded (see Table 1). As it traversed the visible solar disc, the complex and ever-growing spot exploded at least nine more times. Each X-class flare caused a radiation storm and provided conditions for modest aurora-mode propagation. On September 10th and 11th, ruby-red auroras were seen as far south as Arizona.

It is typical during the decline of recent solar cycles to see moments of strong activity, although they are less frequent than in the years centered on a cycle’s maximum. What makes 2005 unique, though, is the strength of these occasional solar flare-ups. The year started immediately on New Year’s Day with the first of many X-class flares! Since then we’ve experienced four severe geomagnetic storms and 14 more X-flares.

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