New Solar Cycle 25 Forecasts and Revision of an Older One

The last month has had a couple of interesting items related to the new solar cycle.  One is the forced retraction of a paper by a researcher whom I've covered; the other is a new forecast from a group I haven't seen, using a new technique.  This technique predicts a better cycle 25 than virtually everyone I've seen, but it has its problems, too.  

To begin with, Watts Up With That reports the recent retraction of a Nature publication on solar cycles, predicting a ‘modern Maunder Minimum’ before 2050.  The paper, by a team including Dr. Valentina Zharkova was published in June 2019 and retracted by the journal March 4, 2020.   I've quoted Dr. Zharkova in these pages several times; perhaps the most detailed description of her work is in November of '18.  

Dr. Zharkova's work is on the solar dynamo, the magnetic fields that create virtually everything we see on the sun.  It began by observing the sun and attempting to come up with a model to explain the patterns we see.  Reviewing this work and trying to see the differences between this and some of her publications which I've talked about in the past, it's very similar to the research published in Nature.  That 2015 prediction was based on two Principal Components measured over perhaps three cycles (~33 years). 

In the current work, she includes more terms of the Principal Components, four terms instead of two.  Adding more terms should produce a better model fit.

The article on WUWT goes into why the paper was retracted by Nature. 

Post publication, a number of astrophysicists pointed out that a key calculation assumption—Earth/Sol barycenter fluctuations are random—was just wrong. Nature editors therefore had no choice but to retract the faulty paper when this was easily verified. (See the linked retraction notice footnotes.)

The WUWT author goes into some detail of what he considers a problem that I also expressed doubt over: they found their four principal components in a 33 year sample of the solar cycles.  My problem with that is the unstated assumption that everything that's visible in the solar dynamo now has always been there, will always be there, and nothing else has ever been in the dynamo.  They extrapolate their 33 years over thousands of years and while I understand constancy is a common assumption in science, I always wonder how well a rare event can be predicted. 

The author invokes Nyquist's sampling theory, but pretty badly.  Some of the commenters did a better job of it.

The other big story was mentioned in the ARRL Letter, their weekly news bulletin, on July 9th.  Just as Dr. Zharkova's technique was newly discovered and applied to the problem of solar activity forecasting, the authors of this paper (pdf) "Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude," applied a new technique.  

The paper notes that recent studies have illustrated a relationship between the sun's 22-year Hale magnetic cycle and the production of sunspot cycle landmarks and patterns, but not the amplitude of the cycle.

"Using discrete Hilbert transforms on 270 years of monthly sunspot numbers to robustly identify the so-called 'termination' events -- landmarks marking the start and end of sunspot and magnetic activity cycles -- we extract a relationship between the temporal spacing of terminators and the magnitude of sunspot cycles," the abstract explains. "Given this relationship and our prediction of a terminator event in 2020, we deduce that Sunspot Cycle 25 will have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of Sunspot Cycle 25 magnitude."

That sounds pretty spectacular, but my skeptical take comes forward.  Cycle 19 is the strongest cycle on record.  Granted that we didn't have the radio technology much before the 30s to determine that, but I'm always skeptical when someone predicts we'll have a repeat of something we know happened once in human history.  It sometimes seems as if every few months someone predicts another Carrington Event.  I'm highly skeptical of those predictions.

The prediction that "Cycle 25 will have a magnitude that rivals the top few since records began" sounds nice, but we get predictions like this almost every cycle.  The last cycle (24) is the only cycle I can't recall reading predictions that it would equal cycle 19.  What they don't say in that extract is that their prediction band is so big that the cycle could approach the strongest cycle on record, but it could also approach the weakest cycle on record.  Look at the plot on the left.  The low end is around Sunspot Number (SSN) of 80.  The consensus predictions for this cycle seem to have it as a duplicate of the previous cycle.  That's stronger than the bottom of the light blue band.  Their high confidence predictions, in the darker blue background, show 25 being markedly better than 24 (circled). 

 

Where does that leave us?  I'm afraid I get nothing out of that new paper making predictions of termination events.  With Dr. Zharkova's paper being retracted, we're left with a consensus like that last link, right above the graphs.  If this newest paper is right, it should be apparent in the next year or two.