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。在过去的15年里，我的研究小组已经在国际舞台上确立了自己的地位，主要是通过制作第一个全球（3D） MHD模拟太阳对流产生规律的类太阳磁周期，最近通过成功地将这些模拟扩展到观测太阳型恒星的恒星周期。另一个重要的和最近的突破是混合发电机模型的发展，允许自一致地详细研究不断变化的表面磁性对磁周期后续演变的影响，这是将太阳数据同化到基于发电机的周期预测模拟的重要过程。提出的研究主要是为了进一步加深我们对太阳（和恒星）磁活动周期的物理理解，主要是通过全球MHD模拟，但也通过几何和动态简化模型，允许很长的时间积分。研究目标包括：(1)了解地磁周期和振幅的物理机制；(2)了解周期变化的起源，包括强烈抑制活动的时期，如17世纪的蒙德极小期；(3)将数据同化到发电机模型中，改进太阳周期预报方案；(4)将数据同化到耀斑能量释放的雪崩模型中，改进太阳耀斑预报方案。

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.