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.

总结太阳是磁星。它的磁场渗透到其上层，大气和大部分太阳系。该磁场内的变化和复杂性，以及在太阳浅内部的相关质量流中，被认为是多种现象的原因。这些范围从黑子的形成和演变，到太阳耀斑和质量弹出，到太阳风的性质的变化以及对电信直接影响并有助于地球上的全球变化的近地环境。尽管它们的重要性，但太阳可变性的原因，磁场的作用以及它们与太阳内部内部材料流的关系尚不清楚。 Heliosemologist通过测量从表面发出的光中的多普勒移位来记录太阳上的低频声波。局部的Heliose术使用这些声波，通过太阳的大量巨型米表示传播，以制造太阳能内部的图像。这些图像揭示了物理特性的复杂变化和流动的复杂模式。通过使用声波直接观察太阳的内部，Heliosemologsist试图理解太阳可变性的起源，其与磁场的关系，并最终能够预测直接影响地球和近乎磨难环境的太阳事件的发生。该项目的目的是为HelioseStology带来一种新的技术方法，该方法将允许在时空和时间上更好地解决图像，而不是使用现有技术。这种新方法是波动方程式层析成像，是由有兴趣以高分辨率对地球进行成像的地震学家开发的，主要是为了为石油行业寻找石油和天然气。该行业已经对这些技术进行了巨大的投资，现在该投资的某些技术成果现在可以应用于新的科学领域。与地球上的地震或人为的来源相反，太阳声的来源不是离散的事件。相反，太阳能源分布在时空和时间上。为了使用此类波来对内部进行成像，现有技术必须在太阳的大区域和大量时间内首先平均数据。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。这些方法还基于射线理论的简化物理学的基础，并且由于这并不能完全解释声波的有限波长，因此它可以损害其在最佳尺度上的分辨率和准确性。在波动层析成像中，在计算机中模拟了波传播的完整物理，并将其用作成像的基础。这种方法避免了其他方法所需的平均值，也避免了与几何光学元件相关的近似值。在一项试点研究中，我们表明，新技术可用于具有分布源的合成太阳能数据。该方法在计算上是要求的，但是即使在3D中，也可以在现代计算机硬件上实现。在这个项目中，我们将开发此技术，以便将其定期应用于本地的Helioseisic数据。我们将在合成数据上测试我们方法的准确性和分辨率，并将其应用于ESA/NASA SOHO卫星的现有数据，并将其应用于计划于2008年推出的NASA SDO任务中收集的新的高分辨率数据。我们特别有兴趣将Sunspots和其他活跃磁性区域的方法应用于Sunspots和Sun the Sun the Sun的其他活动。在项目结束时，我们将发布计算机代码，以便其他正在从事Heliose震动数据的人可以将新方法应用于自己的问题。