The Sun normally follows an 11-year cycle of activity. The current cycle, Cycle 24, is now supposed to be ramping up towards maximum strength. Increased numbers of sunspots and other indications ought to be happening: but in fact results so far are most disappointing. Scientists at the National Solar Observatory (NSO) now suspect, based on data showing decades-long trends leading to this point, that Cycle 25 may not happen at all.
According to a statement issued by the NSO, announcing the research:
An immediate question is whether this slowdown presages a second Maunder Minimum, a 70-year period with virtually no sunspots [which occurred] during 1645-1715.
NASA discusses the sunspot cycle
Alfin has a larger collection of articles discussing the shutdown of the solar cycle
Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715. Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research.
"This is highly unusual and unexpected," says Dr Frank Hill of the NSO. "But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation."
Penn and Livingston observed that the average field strength declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They also observed that spot temperatures have risen exactly as expected for such changes in the magnetic field. If the trend continues, the field strength will drop below the 1,500 gauss threshold and spots will largely disappear as the magnetic field is no longer strong enough to overcome convective forces on the solar surface.
In parallel with this comes research from the US Air Force's studies of the solar corona. Richard Altrock, in charge of this, has found a 40-year decline in the "rush to the poles" – the poleward surge of magnetic activity in the corona.
"Those wonderful, delicate coronal features are actually powerful, robust magnetic structures rooted in the interior of the Sun," Altrock says. "Changes we see in the corona reflect changes deep inside the Sun ...
"Cycle 24 started out late and slow and may not be strong enough to create a rush to the poles, indicating we'll see a very weak solar maximum in 2013, if at all. If the rush to the poles fails to complete, this creates a tremendous dilemma for the theorists ... No one knows what the Sun will do in that case."
According to the collective wisdom of the NSO, another Maunder Minimum may very well be on the cards.
"If we are right," summarises Hill, "this could be the last solar maximum we'll see for a few decades. That would affect everything from space exploration to Earth's climate."
The next few generations of humanity might not find themselves trying to cope with global warming but rather with a significant cooling. This could overturn decades of received wisdom on such things as CO2 emissions, and lead to radical shifts in government policy worldwide.
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