Wave-equation helioseismology

波动方程日震学

• 批准号: PP/E002153/1
• 负责人: Michael Thompson
• 金额: $ 2.85万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=PP%2FE002153%2F1
• 关键词: Wave; equation; helioseismology

Summary The Sun is a magnetic star. Its magnetic field permeates its upper layers, its atmosphere, and much of the solar system. Variations and complexities within this magnetic field, and within related mass flows in the shallow interior of the Sun, are thought to be responsible for a wide range of phenomena. These range from the formation and evolution of sunspots, through solar flares and mass ejections, to changes in the properties of the solar wind and the near-Earth environment that have a direct effect on telecommunications and contribute to global change on Earth. Despite their importance, the causes of solar variability, the role of the magnetic field, and their relationship to the flow of material within the interior of the Sun, are not well understood. Helioseismologists record low-frequency sound waves on the Sun by measuring the Doppler shift in light emitted from the surface. Local helioseismology uses these sound waves, propagating through the upper few tens of mega-metres of the Sun, to make images of the solar interior. These images reveal complicated changes in physical properties, and complicated patterns of flow. By using sound waves to observe the interior of the Sun directly, helioseismologists are attempting to understand the origin of solar variability, its relationship to the magnetic field, and ultimately to be able to predict the occurrence of those events on the Sun that directly influence the Earth and the near-Earth environment. This project aims to bring a new technological approach to helioseismology that will allow images to be generated that are better resolved in both space and time than is possible using existing techniques. This new approach, wave-equation tomography, has been developed by seismologists interested in imaging the Earth at high resolution, principally to aid in the search for oil and gas for the petroleum industry. A huge investment in those techniques has been made by that industry, and some of the technical fruits of that investment can now be applied to a new area of science. In contrast to earthquakes or man-made sources on the Earth, sources of solar sound are not discrete events. Instead the solar source is distributed in both space and time. In order to use such waves to image the interior, existing techniques must first average data over a significant area of the Sun and over a significant time. This averaging necessarily limits the resolution in space and time that such methods can achieve. These methods also base their imaging on the simplified physics of ray theory, and since this does not fully account for the finite wavelength of sound waves, it can compromise both their resolution and accuracy at the finest scales. In wave-equation tomography, the full physics of wave propagation is simulated in the computer and used as the basis for imaging. This approach avoids both the averaging required by other methods, and the approximations associated with geometric optics. In a pilot study, we have shown that the new technique works on synthetic solar data with a distributed source. The approach is computationally demanding, but even in 3D it is achievable on modern computer hardware. In this project, we will develop this technique so that it can be applied routinely to local helioseismic data. We will test the accuracy and resolution of our method on synthetic data, and will apply it to existing data from the ESA/NASA SOHO satellite and to new higher-resolution data to be collected on the NASA SDO mission scheduled for launch in 2008. We are interested particularly in applying the method to data from sunspots and other active magnetic regions on the Sun. At the end of the project, we will release the computer codes so that others who are working on helioseismic data can apply the new methods to their own problems.

太阳是一颗磁性的星星。它的磁场渗透到它的上层，大气层和太阳系的大部分地区。这个磁场的变化和复杂性，以及太阳内部浅层的相关质量流，被认为是造成广泛现象的原因。这些变化包括太阳黑子的形成和演变，通过太阳耀斑和物质抛射，以及太阳风和近地环境特性的变化，这些变化对电信产生直接影响，并促成地球上的全球变化。尽管它们的重要性，太阳变化的原因，磁场的作用，以及它们与太阳内部物质流动的关系，并没有得到很好的理解。日震学家通过测量太阳表面发出的光的多普勒频移来记录太阳上的低频声波。当地日震学利用这些声波，通过太阳上部几十兆米的传播，制作太阳内部的图像。这些图像揭示了物理性质的复杂变化和复杂的流动模式。通过使用声波直接观察太阳内部，日震学家试图了解太阳变化的起源及其与磁场的关系，并最终能够预测太阳上直接影响地球和近地环境的事件的发生。该项目旨在为日震学带来一种新的技术方法，使生成的图像在空间和时间上都比使用现有技术更好地分辨。这种新方法，波动方程层析成像，是由对高分辨率地球成像感兴趣的地震学家开发的，主要是为了帮助石油工业寻找石油和天然气。该行业对这些技术进行了巨大的投资，这些投资的一些技术成果现在可以应用于一个新的科学领域。与地球上的地震或人造声源不同，太阳声源不是离散事件。相反，太阳源分布在空间和时间上。为了使用这种波来对内部进行成像，现有技术必须首先对太阳的重要区域和重要时间的数据进行平均。这种平均必然限制了这种方法可以实现的空间和时间分辨率。这些方法也基于射线理论的简化物理学，并且由于这不能完全解释声波的有限波长，因此它可以在最精细的尺度上损害它们的分辨率和准确性。在波动方程层析成像中，在计算机中模拟波传播的全部物理过程，并将其用作成像的基础。这种方法既避免了其他方法所需的平均，也避免了与几何光学相关的近似。在一项试点研究中，我们已经证明，新技术适用于分布式源的合成太阳能数据。这种方法对计算要求很高，但即使在3D中，它也可以在现代计算机硬件上实现。在这个项目中，我们将开发这种技术，使其可以常规地应用于当地的日震数据。我们将在合成数据上测试我们的方法的准确性和分辨率，并将其应用于欧空局/美国航天局SOHO卫星的现有数据和计划于2008年发射的美国航天局SDO使命收集的新的更高分辨率数据。我们特别感兴趣的是应用该方法的数据从太阳黑子和太阳上的其他活跃的磁性区域。在项目结束时，我们将发布计算机代码，以便其他正在研究日震数据的人可以将新方法应用于他们自己的问题。