Wobbly Universe

25 January 2007, From New Scientist

"There's a dimmer switch inside the sun that causes its brightness to rise and fall on timescales of around 100,000 years - exactly the same period as between ice ages on Earth. So says a physicist who has created a computer model of our star's core.

Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the sun's interior. According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that slight variations should be possible.

He took as his starting point the work of Attila Grandpierre of the Konkoly Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a collaborator, Gábor Ágoston, calculated that magnetic fields in the sun's core could produce small instabilities in the solar plasma. These instabilities would induce localised oscillations in temperature.

Ehrlich's model shows that whilst most of these oscillations cancel each other out, some reinforce one another and become long-lived temperature variations. The favoured frequencies allow the sun's core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says that random interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other."

-end quote- see article for more

Solar Resonant Diffusion Waves as a Driver of Terrestrial Climate Change is the original article in the astrophysics archive. It is clear from this article that Ehrlich's model produces a series of periods of the form 360,000 years / n^2 where n is 1, 2, 3, 4, although the figure 360,000 years seems just a little low. This gives periods corresponding to the 4 main Milankovitch cycles of 400,000, 100,000, 41,000 and 23,000 years. Previously these periods were considered to appear in the climate record because they related to earth orbital and axial dynamics, so the new proposal is a surprise.