SOLARNET Conference: The Many Scales of the Magnetic Sun

The solar magnetic field is generated and sustained by the combined action of turbulent convection and differential rotation. This dynamo process can sometimes lead to magnetic cyclic variabilities, like the solar 11 years cycle. Traces of magnetic cycles have also been detected in other solar-like stars, ranging from a few years to a few tens of years. How is the solar cycle period controlled?
Recent 3D numerical simulations of solar-like stars show that different regimes of differential rotation can be characterized with the Rossby number (advection over Coriolis force). In particular, “anti-solar” differential rotation (fast poles, slow equator) may appear for high Rossby number (slow rotators). If large-scale flows transitions occur during the solar main sequence, we may wonder how the magnetic generation will be impacted.

We present a numerical multi-D study to understand the magnetic field generation and evolution of solar-like stars under various differential rotation regimes, in a Sun in time context. We find that short and local cycles near the surface are favoured for small Rossby numbers (fast rotators), while long and global cycles appear for intermediate (solar-like) Rossby numbers. Slow rotators (high Rossby number) are found to produce statistically steady dynamo with no cyclic activity in most cases considered. We further evaluate energy transfers in these models and quantify that dynamos can be powered by up to 3% of the stellar luminosity, part of it being then available to power surface events. In this regard, future Solar Orbiter observations outside the ecliptic will provide fantastic constraints on solar polar caps magnetic field, and thus on the type of dynamo that our Sun is most likely to operate.