Forecasting Cycle 25—Great Conveyor Belt Theory

The last post reviewed a forecasted solar Cycle 25 based upon measuring the magnetic field of sunspots.   This posting uses the speed of the Sun’s Great Conveyor Belt(GCB) to forecast Cycle 25. This method considers sunspots as an indicator but the GCB speed determines how many sunspots appear.  I am not sure who, but perhaps Dibyendu Nandi of the Indian Institute of Science and Education and Research in Kolkata (aka, Calcutta) and his team  can claim this theory. The GCB has been studied for a number of years.  NASA Science says: “The Great Conveyor Belt is a massive circulating current of fire (hot plasma) within the sun. It has two branches, north and south, each taking about 40 years to complete one circuit.“  “The plasma flows travel along the Sun’s surface and plunge inward at the poles, and reappear again at the Sun’s equator.  When the sunspots begin to decay, surface currents sweep up their magnetic remains and pull them down inside the star; 300,000km below the surface, the sun’s magnetic dynamo amplifies the decaying magnetic fields.  Re-animated the sunspots become buoyant and bob up to the surface like a cork in water—voila! A new solar cycle is born.”

These belts can be likened to the Earth’s ocean currents.

NASA’s artistic sketch of the belt.

A May 2006 posting on Science News has Dr Hathaway predicting that Cycle 24 sunspots numbers would be perhaps greater than Cycle 23 (this part of the prediction is not faring well.) and Cycle 25 would be perhaps half of Cycle 23.  Dr Hathaway said that these predictions were based on a deceleration of these belts to 0.75m/s in the North and 0.35m/s in the south.  He said “We’ve never seen speeds so low”.    Hathaway in a September 2011 posting said:”…….that as the number of sunspots increases on the Sun, the speed of the GCB decreases and vice versa: fewer sunspots and the faster the speed of the Belt.”   This is somewhat contradictory,  because if the GCB speed is slowing down, based on his theory,  there would be more spots.

Dr. Nandi  adds some clarification when he lays out his theory here: “The fast-moving belt rapidly dragged sunspot corpses down to sun’s inner dynamo for amplification. At first glance, this might seem to boost sunspot production, but no. When the remains of old sunspots reached the dynamo, they rode the belt through the amplification zone too hastily for full re-animation.  Sunspot production was stunted.”  Nandi  then adds that late in the decade, “….according to the model, the Conveyor Belt slowed down again, allowing magnetic fields to spend more time in the amplification zone, but the damage was already done.  New sunspots were in short supply.  Adding insult to injury, the slow moving belt did little to assist re-animated sunspots on their journey back to the surface, delaying the onset of Solar Cycle 24.”  

Hathaway’s sunspot predictions are in Red.   Also on this chart, in Pink, are the Cycle 24 sunspot predictions by NCAR’s Mausumi Dikpata and her team based on their observations of the GCB.

Nandi  has made a presentation “Forecasting the Solar Cycle”at the Harvard Smithsonian Center for Astrophysics, Cambridge, USA  but I can not access the paper.

This theory says that the change of speed of the GCB predestines the solar çycle  robustness or lack there of.  For some insight of how they are able to track these plasma flows/GCBs/jet streams, click here.

Like the declining sunspot magnetic field, the theory of the GCB seem to me to be describing consequences of some other forcing that is not known or understood.  I think it likely that Cycle 25 will be weak.  However, until we know more about the functioning of the Sun,  we will be forecasting like the weather casters—tomorrow will be rainy because rain clouds are blowing our way from the west.  Like all of these theories, only time will tell if they are really capable of predicting accurately Cycle strength.

We are not through with Cycle prediction theories.  Next posting will discuss the bicentennial decrease in Total Solar Irradiance (TSI) unbalancing the Earth’s thermal budget.


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