Physical causes and consequences of the solar magnetic activity cycle

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The solar magnetic field is the energy source and dynamical driver of all physical phenomena collectively defining solar activity. The spatiotemporal evolution of the solar magnetic field, in turn, is powered by a hydromagnetic dynamo process, tapping its energy in the flow of electrically conducting fluid within the solar interior, chiefly turbulent convection and differential rotation. This flow-field interaction is a fundamentally nonlinear process, which for solar interior conditions is well-described by the magnetohydrodynamical (MHD) approximation. A very prominent evolutionary timescale is he so-called eleven year solar magnetic activity cycle, associated with the regular polarity reversals of the global solar magnetic field. This cycle modulates the frequency of all geoeffective solar eruptive phenomena, as well as radiative and particulate variability influencing the Earth's upper atmosphere and geospatial environment. Accordingly, understanding and predicting the solar magnetic activity cycle is a cornerstone of space weather research, as well as investigations of phenomena unfolding on much longer timescales (known as space climate).Over the past 15 years my research group has solidly positioned itself on the international scene, primarily through the production of the first global (3D) MHD simulations of solar convection generating regular solar-like magnetic cycles, and more recently via the successfull extensions of these simulations to observed stellar cycles in solar-type stars. Another important and recent breakthrough is the development of a hybrid dynamo model allowing to investigate self-consistently in detail the impact of evolving surface magnetism on the subsequent evolution of the magnetic cycle, an essential process towards solar data assimilation into dynamo-based cycle prediction simulations.The proposed research aims primarily at furthering our physical understanding of the solar (and stellar) magnetic activity cycle(s), primarily through global MHD simulations, but also via geometrically and dynamically simplified models allowing very long temporal integrations. Research objectives include: (1) understanding the physical mechanisms setting the magnetic cycle's period and amplitude; (2) understanding the origin of the cycle's variability, including epochs of strongly suppressed activity, such as the seventeenth century Maunder Minimum; (3) improving solar cycle forecasting schemes by data assimilation into dynamo models; (4) improving solar flare forecasting schemes by data assimilation into avalanche models for flare energy release.