Spring 2006 Issue

PROPAGATION

The Cycle Minimum is Here
Cycle 24 Predicted to be the Best in 50 Years!

 By Tomas Hood, NW7US/AAAØWA

The start of the solar Cycle 23 minimum has officially been declared, signaling the fast approach of the end of the roughly 11-year sunspot cycle. Most likely, the end of the current cycle will be in December 2006, with the start of Cycle 24 occurring in January 2007.

The official declaration of the arrival of solar minimum was made by NASA, whose solar scientists believe that we’re now witnessing the ending of the current sunspot cycle. This assessment is based on the frequent longer periods of solar calm, when for many days at a time the sun has no visible sunspots. The first of these significantly long periods of total solar quiet was the 10-day run starting on January 29, 2006, when there were no sunspots on the visible sun. Nearly the entire month of February passed without sunspots, too. There were sunspots on only nine days in February. During solar minimum whole months can go by without a single sunspot.

February 2006 was the first month in almost ten years with mostly no sunspots. We can now expect this situation to continue for the rest of 2006, until the next cycle, solar Cycle 24, fires up.
Without any significant sunspot activity, there’s very few, if any, solar flaring or coronal mass ejections. When sunspots develop, they tend to be small and not very complex, triggering only minor flares which rarely exceed the C-class X-ray classification. This low solar activity means that VHF radio propagation via the F-layer is non-existent, because the ionosphere can only refract radio signals when it is energized by solar energy.

In May, and during the rest of the year, we still may have occasional sunspots and solar flares. During the first week in April 2006, for instance, we saw K-index readings of 6, indicating significant geomagnetic activity. This storm-level geomagnetic activity triggered a bit of aurora, which could have been enough to support aurora-mode propagation and sporadic-E propagation via the auroral ionization. During this same period in April, the 10.7-cm flux readings reached 100.

Historically, during each of the last three solar cycle minima in 1976, 1986, and 1996, the sun unleashed at least one X-class flare and produced at least one giant sunspot. However, the overall condition is a very quiet sun. Perhaps we’re in store for a surprise event that could wake up VHF activity during this period (May, June, and July).

Solar Cycle 24—The Best in 50 Years

In March 2006, a team led by Mausumi Dikpati of the National Center for Atmospheric Research (NCAR) announced that the new solar Cycle, the 24th since sunspots were faithfully recorded, will be the most intense solar maximum in 50 years. Researcher Dikpati says, “The next sunspot cycle will be 30 percent to 50 percent stronger than the previous one.” If this prediction is correct, the solar activity in just a few years will be second only to the historic solar cycle maximum of 1958.

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