.....There has been quite a bit of news about a predicted grand minima in solar activity. We recently reported on a conference where three lines of evidence were presented, seeming to point to a future disappearance of sunspots, perhaps like the dreaded Maunder Minimum. I am not unbiased in this regard, and like most radio amateurs, yearn for high solar activity. Alas, a return of Solar Cycle 19, the granddaddy of them all, seems elusive. But there is some dissent regarding these predictions of no sunspots, which gives us hope.
On Wednesday, I spoke with Dr. Douglas Biesecker, an astrophysicist at the NOAA Space Environment Center in Boulder. He was mentioned in the
Solar Update for June 17, dissenting from the assertion that evidence points toward sunspots disappearing or another Maunder Minimum in our future.
He mentioned something called a Gleissberg Cycle. When we do a really long smoothing of sunspot numbers, the smoothed sunspot numbers we are familiar with -- the data used in those nice graphs of sunspot cycles -- average data over 13 months. So every place you look on the graph doesn’t show the variation that occurred during that month, but instead averages data over more than a year, to smooth out all the noise of daily variations. But what would happen if you smoothed the numbers over a much longer period, say 11 years? Could you find some periodicity that would suggest a cycle of cycles or perhaps predict clusters of decades with low or high solar activity?
Gleissberg cycles suggest a periodicity of about 87 years, and some have studied these to try to predict general levels of solar activity over multiple decades. But if a cycle is 87 years long -- and we only have about 256 years of directly observed solar data -- the most we could look at would be less than three cycles. That isn’t enough data to make even crude speculative projections.