Rieger, Schwabe, Suess-de Vries: The sunny beats of resonance

by Frank Stefani (Helmholtz-Zentrum Dresden - Rossendorf)

Tuesday 1 Oct 2024, 15:00 → 16:00 Europe/Stockholm

https://stockholmuniversity.zoom.us/j/940229961

 

In the first part of the talk, we discuss a model of the solar dynamo that tries to explain its various periodicities on widely different time scales in a self-consistent manner. Starting with Rieger-type periods, we show that the two-planet spring-tides of Venus, Earth and Jupiter can excite magneto-Rossby waves in the solar tachocline with periods between 100 and 300 days and amplitudes of m/s or even more. We further show that the dynamo-relevant quadratic action of these waves contains a beat period of 11.07 years, and that its axisymmetric part might indeed be strong enough to synchronize the entire solar dynamo via parametric resonance. Then we argue that a second beat between the arising Hale cycle and the 19.86-year periodic motion of the Sun around the barycenter of the solar system may explain the longer-term Gleissberg and Suess-de Vries cycles. The spectrum emerging from this double-synchronized dynamo model shows amazing correspondence with climate-related data.

In the second (and shorter) part of the talk, we examine the present status of the DRESDYN precession-driven dynamo experiment. One of its motivations stems from the poorly understood spin-orbit coupling effect in our solar dynamo model. We discuss the combined numerical and experimental efforts to identify dynamo-optimizing precession ratios and nutation angles, and illustrate the steps in the construction of the machine that is presently under commissioning.