Helioseismic Probing of Convection Zone Dynamics

研究太阳对流区的动力学需要在日震逆理论方面取得重大进展，以便开发新的分析技术，这是充分利用全球振荡网络小组和其他日震观测提供的高度振荡数据所必需的。 波场扭曲和频率分裂的高度振荡应该允许一个测量大规模的流动和相关的温度波动在对流区直接在太阳表面之下。 本项目将开发和完善先进的反演技术，以解释观测到的频率分裂和扭曲波场以下两种方法。 第一种方法采用从3-D傅立叶变换获得的功率谱的环形图来进行流场和热场的马赛克映射，这些环形的详细形状和位移取决于每个小区域内的平均速度及其梯度。 最近，利用初步的环形图分析发现了地表以下的纬向喷流，这为这项工作增添了强大的动力。 第二种方法使用声波序列的希尔伯特变换，分析它们的相位和振幅变化，以检测由底层温度和磁场引起的波传播速度的变化。 相位信息所提供的希尔伯特变换的扭曲波包，因为它们通过一个组件的对流细胞作为输入到反演程序，以获得声速变化的空间地图。 环形图和希尔伯特波列分析是互补的：环形分析是一个强大的局部过程，它简化了某些全局信息，而希尔伯特技术更复杂，在广泛分离的流动区域中关联相位，以获得比傅立叶技术更高的空间分辨率。 这两种方法对于了解太阳对流区的运作方式都是必不可少的。 这种程序将首先用于国家太阳观测台目前利用高度日震仪获得的高度振荡数据，以便将其发展为完善的工具，供以后用于其他日震数据集，包括由国家科学基金资助的GONG项目和SOHO航天器上的SOI-MDI仪器提供的数据集。 ***

Toomre 9417337 The study of the dynamics of the solar convection zone requires substantial advances in helioseismic inverse theory in order to develop new analysis techniques that are needed to make good use of the highdegree oscillation data to be provided by the Global Oscillations Network Group (GONG) and by other helioseismology observations. The wave-field distortions and frequency splittings of high-degree oscillations should allow one to measure large-scale flows and associated temperature fluctuations in the convection zone immediately beneath the surface of the sun. This project will develop and refine advanced inversion techniques to interpret the observed frequency splittings and distortions in the wave field following two approaches. The first employs ring diagrams of power spectra obtained from 3-D Fourier transforms to do mosaic mapping of the flow fields and thermal fields, with the detailed shapes and displacements of such rings depending upon the averaged velocities and their gradients within each of the small areas being assessed. The recent potential discovery of zonal jets below the surface using preliminary ring-diagram analysis adds strong impetus to this work. The second method uses Hilbert Transforms of acoustic wave trains, analyzing their phase and amplitude variations to detect changes in wave propagation speeds caused by underlying temperature and magnetic fields. Phase information provided by the Hilbert transform of distorted wave packets as they travel through an assembly of convection cells is used as input to inversion procedures to obtain spatial maps of sound-speed variations. The ringdiagram and Hilbert wave-train analyses are complementary: ring analysis is a robust local procedure which sacrificeq certain global information for simplicity, whereas the Hilbert technique is more sophisticated, relating phases in widely separated regions of the flow to obtain higher spatial resolution than is possible by Fourier techniques. Both methods are essential to understanding how the solar convection zone operates. Such procedures will be first employed on high-degree oscillation data now being obtained at the National Solar Observatory with the HighDegree Helioseismometer (HDH) in order to develop them as refined tools for later use on other helioseismic data sets, including those to be provided by the NSF-funded GONG project and by the SOI-MDI instrument on the SOHO spacecraft. ***