Physical causes and consequences of the solar magnetic activity cycle

太阳磁场是决定太阳活动的所有物理现象的能量来源和动力驱动因素。反过来，太阳磁场的时空演变是由一个磁发电机过程驱动的，它的能量来自太阳内部的导电流体流动，主要是湍流对流和微分旋转。这种流场相互作用基本上是一个非线性过程，对于太阳内部条件，可以用磁流体动力学（MHD）近似很好地描述。一个非常突出的进化时间尺度是所谓的11年太阳磁活动周期，与全球太阳磁场的定期极性逆转有关。这一周期调节了所有对地球有效的太阳喷发现象的频率，以及影响地球上层大气和地理空间环境的辐射和颗粒变率。因此，理解和预测太阳磁场活动周期是空间天气研究的基石，也是在更长的时间尺度（即空间气候）上展开的现象调查的基石。

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.