[font face=Serif][font size=5]Royal Astronomical Society’s National Astronomy Meeting 2015 – report 4[/font]

Posted on 9 July 2015 by Astronomy Now

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The two-hearted Sun beckons new ‘mini ice-age’

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Our Sun has an approximately 11-year activity cycle. During peak periods, it exhibits lots of solar flares and sunspots. Magnetic bubbles of charged particles (coronal mass ejections) may burst from the surface during this period, streaming material into space. These ejections can affect satellites and powerlines on Earth. During lull periods, such activity may almost stop altogether. But the 11-year cycle isn’t quite able to predict all of the Sun’s behaviour — which can seem erratic at times. Zharkova and her colleagues (Professor Simon Shepherd of Bradford University, Dr Helen Popova of Lomonosov Moscow State University, and Dr Sergei Zarkhov of Hull University) have found a way to account for the discrepancies: a ‘double dynamo’ system.

The Sun, like all stars, is a large nuclear fusion reactor that generates powerful magnetic fields, similar to a dynamo. The model developed by Zharkova’s team suggests there are two dynamos at work in the Sun; one close to the surface and one deep within the convection zone. They found this dual dynamo system could explain aspects of the solar cycle with much greater accuracy than before — possibly leading to enhanced predictions of future solar behaviour. “We found magnetic wave components appearing in pairs; originating in two different layers in the Sun’s interior. They both have a frequency of approximately 11 years, although this frequency is slightly different [for both] and they are offset in time,” says Zharkova. The two magnetic waves either reinforce one another to produce high activity or cancel out to create lull periods.

She and her colleagues used magnetic field observations from the Wilcox Solar Observatory in California for three solar cycles, from the period of 1976 to 2008. In addition, they compared their predictions to average sunspot numbers — another strong marker of solar activity. All the predictions and observations matched closely. Their predictions using the model suggest an interesting longer-term trend beyond the 11-year cycle. It shows that solar activity will fall by 60 percent during the 2030s, to conditions last seen during the Maunder Minimum of 1645-1715. “Over the cycle, the waves fluctuate between the Sun’s northern and southern hemispheres. Combining both waves together and comparing to real data for the current solar cycle, we found that our predictions showed an accuracy of 97 percent,” says Zharkova.

The model predicts that the magnetic wave pairs will become increasingly offset during Cycle 25, which peaks in 2022. Then during Cycle 26, which covers the decade from 2030-2040, the two waves will become exactly out of synch, cancelling one another out. This will cause a significant reduction in solar activity. “In cycle 26, the two waves exactly mirror each other, peaking at the same time but in opposite hemispheres of the Sun. We predict that this will lead to the properties of a ‘Maunder minimum’,” says Zharkova.

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