A study was published in 2012, “Sudden transitions and grand variations in the solar dynamo, past and future” by Cornelis DeJager and Silvia Duhan . The authors attempt to predict whether Solar Cycle 25 will transition to a “Grand Minimum” or “Regular “ Episode. They believe the Sun is transitioning from a “Grand Maximum” to one or the other aforementioned Episodes. This study is being used because their prediction was based upon knowing the Solar Cycle 24’s maximum Sunspot number which we now have.
First a look at the “Episodes” that the authors have placed the Solar Cycles from 1620 to the present.
This an interesting diagram so it is worth pointing out some of the details. The International Smoothed Sunspot number at the time of the Solar Cycle maximum, (Rmax) for each, is noted on the diagram with a star.
Maunder Grand Minimum was a time of exceptionally cold global temperatures. That Episode is characterized by Rmax at or near the zero line. There were 5 Cycles (each a full Schwabe 11 year cycle) with little or no Sunspots.
At the other end is the Grand Maximum episode where the sunspot numbers Rmax were uniformly high with Solar Cycle 19 holding the record with Rmax of 201. The last completed Solar Cycle was Cycle 23. The global temperatures during this period have been the highest of any time during this period beginning in 1620.
The Regular Episode is one where most of the RMaxs were in the neighborhood of the”standard”. During the Regular Episode, the Dalton Minimum occurred (note by the green D). This was a period of global temperature cooling, but it was a not a deep or sustained period such as occurred during the Maunder Minimum.
There are only 24 named Solar Cycles. Those that are shown in the Maunder Minimum Episode are reconstructed from proxies such as C14 and Be.
Finally in the chart are two triangles. These are the author’s 2011 predictions of Solar Cycle 24’s Rmax .
The work they have done leads them to believe that the Rmax of Solar Cycle 24 and the aa-max geomagnetic index from Solar Cycle 23 will allow them to predict the nature of the following Episode. The authors said that their Solar Cycle 24 Rmax would be 62 +/- 12. If the actual was at the high end, 74, they predict the Episode would be Regular. If it was at the low end, 50, they predicted that it would be a Maunder Minimum Episode.
We do have Solar Cycle 24 Rmax and it will be no lower than 82. So, Regular it is.
They expected the next Episode to be Regular. The authors take the Hallstatt Periodicity seriously. The Hallstatt is a 2300 yearlong sine wave. According to theory, Grand Minimum can only occur in the negative phase. The curve entered the positive phase around the year 1935.
The Hallstatt Periodicity is shown below.
Most solar scientists seek some correlation that seems to provide the solution to the puzzle. Before Solar Cycle 24 took off, most predictions were Rmax in the 100+ range. Few predicted the 80’s for the Rmax. They were saying it would be like or bigger than Cycle 23. Now most of them are predicting Cycle 25 Rmax to be lower than Cycle 24. Thus the next cycle will look like the current cycle. Not too bad a way to go. The weather forecasts work on that premise. What is obvious, is that the Sun is still a mystery.
A final word, on the authors work: It is a nice piece of explaining the Sun’s dynamics. I suggest you read the report. Furthermore, there are two DVDs that illustrate the Solar Dynamo. One is “Toroidal and Poloidal Magnetic Fields” and the other is “Plasma Flows”.
I am having trouble with links. So if you want to read the report use http://www.swsc-journal.org/articles/swsc/abs/2012/01/swsc120009/swsc120009.html
for the DVDs please use these
I may put together a summary of their work because they explain the “dynamo, the various solar magnetic fields, the geomagnetic field (for which aa-min is a longstanding measurement) , nT, etc. Reporting on studies can be a lot of work when the objective is to make it a “readers digest” version.