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Solar and Planetary Physics at Newcastle University

纽卡斯尔大学太阳与行星物理学

基本信息

批准号：
ST/W001039/1
负责人：
Celine Guervilly
金额：
$ 46.32万
依托单位：
Newcastle University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2022
资助国家：
英国
起止时间：
2022 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FW001039%2F1
关键词：
Solar Planetary Physics Newcastle University

项目摘要

The proposed research programme consists of two projects that aim to explain some of the surprising features of the magnetic fields of the Sun and planets.In the first project, we shall address one of the fundamental questions relating to solar magnetism. The solar surface often contains dark features, known as sunspots, that are the sites of strong, localised magnetic fields. The surface distribution of sunspots follows a well-known cyclic pattern, with zones of sunspot emergence (which are restricted to low latitudes) migrating equatorwards over an 11 year period. It is believed that sunspots are the surface manifestation of an underlying large-scale magnetic field that is buried deep with the solar interior. This magnetic field is generated and maintained by the motions of the plasma within the solar interior, via a (so-called) dynamo mechanism. However, this solar dynamo process is not fully understood. Our aim is to determine the extent to which the latitudinal distributions of sunspots truly reflects the latitudinal distribution of the subsurface large-scale field (and hence the extent to which these surface observations constrain models of the solar dynamo). To achieve this, we will be studying magnetic buoyancy, which is the process by which magnetic flux is transported from the deep interior to the solar surface. This will be investigated via a combination of analytical and numerical techniques. For the first time, the initial magnetic field distributions for the numerical simulations of this process will be derived from existing dynamo models. We shall determine which of these could produce a sunspot distribution that is consistent with solar observations (which would be an important step forward for this area). A better understanding of the solar dynamo and the cyclic activity that it produces would considerably enhance our understanding of space weather and many other solar magnetic phenomena. Our second project concerns planetary magnetic fields. The magnetic field of a planet is generated deep in its interior, in the core which is composed of an electrically conducting fluid (mainly liquid iron for rocky planets and metallic hydrogen for gas giants). This conducting fluid swirls around due to convection as the planet gradually cools down. These motions generate electric currents that induce the magnetic field through a dynamo process. Planetary evolution models indicate that, in many planets of our solar system, such as Mercury, the Earth and Saturn, the outermost part of the core might not be convective, that is the mean variation of density with depth is stable to overturning convection. This stable layer is not at rest though: the density perturbations depend both on the temperature and the chemical composition of the fluid and this can lead to vertical flows. This happens in addition to horizontal flows that are driven by latitudinal variations of density. All these motions can distort the magnetic field produced deeper in the core by the dynamo effect and passing through the stable layer. The effects of the horizontal flows on the magnetic field have been studied for several decades and they are fairly well understood. In particular, they are used to explain a surprising feature of Saturn's and Mercury's magnetic fields, namely that their magnetic field is axisymmetric, i.e. it lacks longitudinally-dependent features. However, the vertical motions have never been studied before in the context of planetary cores, so we do not know what their effect is on the magnetic field. In this project, we will address this issue by studying the motions of the stable layer in computer simulations that model the outer region of the core. The main objectives of the work are to determine the size and flow speed of the motions, and to predict how they modify the planet's magnetic field.

拟议中的研究计划包括两个项目，旨在解释太阳和行星磁场的一些令人惊讶的特征。在第一个项目中，我们将讨论与太阳磁性有关的一个基本问题。太阳表面通常包含深色的特征，即太阳黑子，它们是强大的局部磁场的所在地。太阳黑子的地表分布遵循一个众所周知的周期模式，黑子出现区（仅限于低纬度地区）在11年的周期内向赤道迁移。据信，太阳黑子是深埋在太阳内部的大规模磁场的表面表现。这个磁场是由太阳内部等离子体的运动产生并维持的，通过一个（所谓的）发电机机制。然而，这个太阳能发电机的过程还没有被完全理解。我们的目的是确定太阳黑子的纬向分布在多大程度上真实地反映了地下大尺度场的纬向分布（从而确定这些地表观测对太阳发电机模型的约束程度）。为了实现这一目标，我们将研究磁浮力，这是磁通量从太阳内部深处传输到太阳表面的过程。这将通过分析和数值技术的结合进行调查。这一过程数值模拟的初始磁场分布将首次从现有的发电机模型中推导出来。我们将确定其中哪一个可以产生与太阳观测相一致的太阳黑子分布（这将是该领域向前迈出的重要一步）。更好地了解太阳发电机及其产生的周期活动将大大提高我们对空间天气和许多其他太阳磁场现象的理解。我们的第二个项目涉及行星磁场。行星的磁场产生于其内部深处，在由导电流体组成的核心（岩石行星主要是液态铁，气体巨星主要是金属氢）。当行星逐渐冷却时，这种导电流体由于对流而旋转。这些运动产生电流，通过发电机过程感应磁场。行星演化模型表明，在我们太阳系的许多行星中，如水星、地球和土星，核心的最外层可能不是对流的，即密度随深度的平均变化稳定到推翻对流。然而，这个稳定层并不是静止的：密度的扰动取决于温度和流体的化学成分，这可能导致垂直流动。除了由密度的纬度变化驱动的水平流动之外，还会发生这种情况。所有这些运动都会使磁芯深处由发电机效应产生的穿过稳定层的磁场发生畸变。水平流对磁场的影响已经研究了几十年，并得到了很好的理解。特别是，它们被用来解释土星和水星磁场的一个令人惊讶的特征，即它们的磁场是轴对称的，也就是说，它没有纵向依赖的特征。然而，以前从未在行星核心的背景下研究过垂直运动，所以我们不知道它们对磁场的影响。在这个项目中，我们将通过研究稳定层在模拟地核外部区域的计算机模拟中的运动来解决这个问题。这项工作的主要目标是确定运动的大小和速度，并预测它们如何改变地球的磁场。