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.

拟议的研究计划由两个项目组成，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，我们将解决与太阳磁性有关的基本问题之一。太阳能表面通常包含暗特征，称为黑子，它们是强，局部磁场的位置。黑子的表面分布遵循众所周知的循环模式，在11年的时间内迁移了赤道的黑子出现区（仅限于低纬度）。据信，黑子是一个基础大规模磁场的表面表现，该磁场被太阳内部埋在深处。该磁场是通过太阳能内部的血浆的运动来生成和维持的，该磁场是通过（所谓的）发电机机制生成的。但是，这种太阳能发射过程尚未完全理解。我们的目的是确定黑子的纬度分布在多大程度上反映了地下大规模场的纬度分布（因此，这些表面观测限制了太阳能发电机的模型的程度）。为了实现这一目标，我们将研究磁性浮力，这是将磁通量从深内部传输到太阳表面的过程。这将通过分析和数值技术的组合进行研究。该过程的数值模拟的初始磁场分布将首次从现有的发电机模型中得出。我们将确定其中哪一个可以产生与太阳观测一致的黑子分布（对于该区域来说将是向前迈出的重要一步）。更好地了解太阳能发电机及其产生的环状活性将大大增强我们对太空天气和许多其他太阳磁现象的理解。我们的第二个项目涉及行星磁场。行星的磁场在其内部深处产生，该芯由芯组成，该核心由电导的流体（主要是岩石行星的液态铁和气体巨头的金属氢铁）。随着行星逐渐冷却，这种传导流体由于对流而旋转。这些运动会产生通过发电机过程诱导磁场的电流。行星演化模型表明，在我们太阳系的许多行星中，例如汞，地球和土星，核心的最外部部分可能不是对流的，那就是与深度的平均密度变化相对于对流的稳定。但是，该稳定层并没有静止：密度扰动均取决于流体的温度和化学成分，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外，这种情况还会发生。所有这些运动都会通过发电机效应并穿过稳定层，使芯中产生的磁场更深。水平流对磁场的影响已经研究了几十年，并且对它们的理解相当多。特别是，它们被用来解释土星和水星的磁场的令人惊讶的特征，即它们的磁场是轴对称的，即缺乏纵向依赖的特征。但是，垂直运动从未在行星岩心的背景下进行过研究，因此我们不知道它们对磁场有什么影响。在这个项目中，我们将通过研究对核心外部区域进行建模的计算机模拟中稳定层的运动来解决此问题。工作的主要目标是确定运动的大小和流速，并预测它们如何修改行星的磁场。