Fall 2008 Issue

VHF PROPAGATION

Sleeping on the Job . . .

By Tomas Hood, NW7US

Figure 1. After weeks of a spotless sun and very few sunspots

this entire year, SOHO observed an active region (seen here on September 23, 2008) with the first new cycle sunspot since May 10, 2008. (Source: SOHO)

Perhaps you’ve heard the speculation that our local star is in a coma. Not only amateur radio operators, but now the general press, are picking up the solar buzz, wondering out loud if the sun is in hibernation with a seemingly longer than usual solar cycle minimum. Where are the sunspots? Where’s the activity of a new solar cycle? “We’re going to see another Maunder Minimum and a mini-ice age!”

Really? The Maunder Minimum occurred during the period starting in 1645 and ending in 1715, an incredible 70 years during which sunspots were rarely observed. To the observer, this period is void of any evidence of 11-year solar cycles. What’s more, this period coincided with the famous “Little Ice-Age,” a series of extraordinarily cold winters occurring in the Northern Hemisphere. Is a new Maunder Minimum unfolding on our watch?

A fair amount of chatter developed during August 2008 because it was the first time since 1913 that there was a month or more between sunspot appearances. Certainly, it stood out as unique because it was the first time that a whole calendar month went by without observed sunspots. In a practical sense, however, this is not that remarkable; calendars mark arbitrary beginnings and endings, and a 30-day period occurring at any time is just that—30 days without sunspots. Also, such periods are not uncommon during the solar cycle minimums of the past.

On September 11 a sunspot developed that ended a period of 52 continuous days with no spots. This is the fourth longest spot-free period on record. Both May and June 1913 were spotless, in a continuous spotless run of 92 days from April 8 to July 8. Cycle 19 was the biggest solar cycle on record, and it is interesting to note that it was preceded by long periods without spots. There was a 26-day spotless run from February 15 to March 4, 1953, followed by 27 days from January 12 through February 7, 1954, and 30 days beginning on June 3, 1954 and running through July 2.

Then, on September 22, 2008, SOHO (the Solar & Heliospheric Observatory) observed an active region with the first new-cycle sunspot since May 10, 2008 (figure 1). It had both the magnetic orientation and the high-latitude position of a sunspot belonging to solar Cycle 24.

Recent sunspots belong to either the dying Cycle 23 or to the new Cycle 24. How do we know which cycle a sunspot belongs to? Sunspots are classified based on the magnetic polarities occurring in the complex structures within the sunspot group. When one cycle merges into the next, the magnetic polarities reverse. The latest sunspots are more often occurring with the magnetic polarities consistent with the new solar Cycle 24.

Clearly, the new cycle has begun, even though it seems that the period of calm between Cycle 23 and 24 is unusually long. This sunspot, and the shorter time between recent sunspots, appears to indicate that our sun is waking up from a more normal-looking cycle minimum.

David Hathaway, NASA solar physicist, has reported that the quiet of 2008 is not the second coming of the Maunder Minimum. “We have already observed a few sunspots from the next solar cycle,” he says. “This suggests the solar cycle is progressing normally.”

During a solar cycle maximum, typically lasting several years, huge sunspots and intense solar flares are a daily occurrence. This in turn triggers spectacular auroras that at times are observable in Florida and New Zealand. VHFers enjoy such periods of intense activity because of the related modes of propagation—bouncing VHF signals off the E-layer during aurora or establishing DX contacts by way of a highly energized F-layer. I recall driving in my vehicle with a basic 6-meter mobile whip hooked up to an ICOM IC-706MIIG and having a reasonably long conversation with a famous bass player in a southern rock band who was traveling somewhere in the southeastern United States. While the solar maximum of Cycle 23 was not as intense as Cycle 22, there were some memorable moments in the years around 2000–2002.

During solar cycle minimums quite the opposite occurs. Solar flares are almost nonexistent, while whole weeks or even months go by without a single tiny sunspot anywhere on the sun. While there is continual coronal-hole activity (figure 2), which may trigger some aurora, the intensity and frequency of significant events that birth great VHF moments are rare at this point between solar cycles.

With the sun being so quiet lately, it seems that amateur radio operators are growing restless, asking the question, “Isn’t this an unusually lengthy solar minimum?” With the media picking up on these mumblings, many are speculating that it is longer than usual and that perhaps something very significant is occurring.

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