RUI: Magnetic Diffusivity in a Predictive Solar Dynamo Model

理解太阳活动周期仍然是太阳物理学的关键问题之一。观测到的磁场活动，如太阳黑子周期和磁场逆转，会产生太阳耀斑和日冕物质抛射，对地球产生重大影响。物理学家普遍认为，磁流体发电机通过在太阳对流区(太阳外部30%)产生和改变磁场来产生观察到的11年活动周期。太阳能发电机理论已经取得了进展，计算模型现在可以(在一定程度上)用作预测工具。太阳能发电机依赖于磁等离子体的剪切、浮力、扭曲和流动，磁等离子体是构成太阳的高温电离气体。太阳能发电机最不为人所知的一个方面是太阳本身的物质属性--磁扩散系数，它会导致磁场的变化，而它本身又会受到动态磁场的影响。为了更全面地理解太阳发电机，需要更全面地了解对流区的磁扩散率及其对太阳磁场演变的影响。这不仅是太阳物理学和磁流体力学中一个有趣的理论问题，而且对于对太阳活动敏感的技术(从通信卫星到电网)以及理解可变太阳对我们生物圈的影响也具有实际意义。在这里，一个经过验证的太阳发电机模型将得到改进，以更好地预测未来的太阳周期。二维、非线性、运动的通量输运发电机模型将被用来研究由于温度、湍流和局部磁场强度的变化等因素导致的半径、纬度和时间的扩散率变化的详细原因和影响。齐塔博士将开展的研究将包括重要的新物理学，如扩散系数的动态磁猝灭，以及由于扩散系数梯度而产生的磁平流。对每种影响的系统评估，以及与其他关键发电机元素的比较，将加深对太阳能发电机的基本机制的了解。她的研究将直接有助于太阳物理学的关键目标，包括了解磁场如何在太阳内部出现、分布和消失；以及量化该系统在太阳周期内的物理、动力学和行为。这项研究将产生(1)基于物理的扩散率模型，供太阳能发电机建模人员使用；(2)改进的发电机模型，用于预测未来的太阳活动周期。这项工作还可以阐明其他恒星、星系和聚变等离子体中的发电机；以及在太阳色球和日冕中磁能转化为热的机制，因为这些都需要更好地了解磁扩散系数。本科生将直接参与所有阶段的研究。与国家大气研究中心高海拔天文台正在进行的科学合作将使学生获得高质量的研究体验。齐塔博士还积极参与公共科学素养和对女孩的科学推广活动，她所在的机构是向代表不足的群体的学生推广科学知识的先驱。像这里支持的工作这样的研究项目通常会被纳入跨学科的大学课程。最后，该项目将加强长青学院近年来与高海拔天文台合作建立的太阳物理研究基础设施。

Understanding the solar activity cycle remains one of the key problems in solar physics. Observed magnetic activities, such as sunspot cycles and magnetic field reversals, produce solar flares and coronal mass ejections, with significant influences on the Earth. Physicists generally believe that a magnetohydrodynamic dynamo produces the observed 11-year activity cycle by generating and changing magnetic fields in the solar convection zone (the outer 30% of the Sun). Progress has been made in solar dynamo theory to the point that computational models may now be used as predictive tools (to a certain extent). The solar dynamo depends on the shearing, buoyancy, twisting and flows of magnetic plasma, the hot ionized gas that makes up the Sun. One of the least understood aspects of the solar dynamo concerns a material property of the Sun itself - the magnetic diffusivity, which contributes to changes in magnetic fields, and is itself changed by dynamic magnetic fields. A more complete understanding of the magnetic diffusivity in the convection zone, and of its effects on the evolution of solar magnetic fields, is required to more fully understand the solar dynamo. This is not only an interesting theoretical problem in solar physics and magnetohydrodynamics, it is also of practical importance to technologies that are sensitive to solar activity (from communications satellites to power grids), and to understanding the impact of the variable Sun on our biosphere.Here, a proven solar dynamo model will be improved to better predict future solar cycles. The two dimensional, nonlinear, kinematic flux-transport dynamo model will be used to investigate the detailed causes and effects of diffusivity variations in radius, latitude, and time, due to factors such as temperature, turbulence, and changes in the local magnetic field strength. Dr. Zita will carry out investigations that will include important new physics such as dynamical magnetic quenching of diffusivity, and magnetic advection due to diffusivity gradients. Systematic evaluation of each effect, and comparison with other key dynamo elements, will deepen insight into the fundamental mechanisms of the solar dynamo. Her investigations will contribute directly to key goals in solar physics, including understanding how magnetic fields appear, distribute, and disappear from their origin in the solar interior; and quantification of the physics, dynamics, and behavior of the system over the solar cycle. The research will produce (1) physics-based diffusivity models for use by solar dynamo modelers and (2) an improved dynamo model for prediction of future solar cycles. This work can also illuminate dynamos in other stars, galaxies, and fusion plasmas; and mechanisms by which magnetic energy can be transformed into heat in the solar chromosphere and corona, as these all require better understanding of magnetic diffusivity. Undergraduates will be directly involved in the research at all stages. Ongoing scientific collaborations with the High Altitude Observatory at the National Center for Atmospheric Research will give students access to high quality research experiences. Dr. Zita is also active in public science literacy and science outreach to girls, and her home institution is a pioneer in outreach to students from underrepresented groups. Research projects such as the work supported here are routinely integrated into interdisciplinary college curricula. Finally, the project will strengthen the infrastructure for solar physics research, established in recent years at Evergreen College in the collaboration with the High Altitude Observatory.