Code & Data for: High frequency Faraday rotation observations of the solar corona

Published in 2007, Elizabeth A. Jensen's disseration included several appendices. Appendix F consisted of CDs with the raw radio frequency data used for the analysis and MATLAB processing codes. Appendix C consisted of total electron content data collected during portions of the observing via Differenced Range Versus Integrated Doppler. The receiving antenna array was the Deep Space Network in Goldstone, CA. Source Manuscript: Proquest Dissertations And Theses 2007. Section 0031, Part 0606 264 pages; [Ph.D. dissertation].United States -- California: University of California, Los Angeles; 2007. Publication Number: AAT 3268543. Source: DAI-B 68/06, Dec 2007. https://ui.adsabs.harvard.edu/abs/2007PhDT.........4J/abstract Abstract The million degree solar corona generates the solar wind that in turn controls the Earth's "space weather". The solar coronal magnetic field within 0.25AU (60 solar radii) plays a critical role in the acceleration but is largely "invisible", and can presently only be measured by the Faraday rotation of high frequency electromagnetic radiation. Faraday rotation is the observed rotation in the plane of polarization of an EM wave as it traverses a magnetized medium. The amount of observed Faraday rotation is the integration along the propagation direction of the product of the component of the magnetic field parallel to the propagation vector and the electron density. Faraday rotation is clearly useful for measuring the solar coronal magnetic field. As a remote observation, Faraday rotation measurements require careful consideration of the medium in the analysis. This thesis details the theory of Faraday rotation, previous experiments observing Faraday rotation using the carrier signal from a spacecraft in superior conjunction, the equipment used for the Cassini Faraday rotation observations, the signal analysis and steps taken to acquire a Faraday rotation observation from radio frequency data, the model used to fit the observations, all ancillary data required for these steps, and all the code created for this purpose. The data and code are provided in the attached DVD media. All previous Faraday rotation experiments observed coronal mass ejections (CMEs) producing either 'W' or sigmoid features. These observations are reproduced herein using a Taylor-state flux-rope model crossing the line of sight at different sizes, twist, and orientations, showing that Faraday rotation can be used to measure the magnetic field of CMEs. Using a forward model to fit Faraday rotation and columnar electron density observations, a first order investigation into force balance in the solar corona was conducted. From these fits, the gradients in the magnetic and thermal pressure and the gravitational force per volume were calculated. For the solar wind to escape the gravitational force of the Sun, the magnetic and thermal pressure gradients must dominate. We show from the fits on 2002 June 20 that small adjustments to the PFSS model can provide the necessary magnetic field strengths to supply the needed pressure for solar wind flow; however, the fits from June 21st cannot. The closest approach of the June 21st measurements were all below the source surface of 2.5 solar radii indicating a problem in the use of the PFSS model to determine the structure of the coronal magnetic field below the source surface. Large amplitude 4 minute period Alfven waves have been observed in Helios and Cassini Faraday rotation observations. Using a simple open-ended box model through which magnetohydrodynamic waves can propagate, it is demonstrated that the combination of Faraday rotation and columnar electron density observations can distinguish Alfven waves due to their lack of fluid perturbation. It is also shown that the 2nd harmonic in the Faraday rotation observations is the result of the electron density fluctuation in the magnetosonic (fast and slow) modes. This demonstrates that previous Helios observations producing the 2nd harmonic were MHD magnetosonic waves. Cassini's observation of an Alfven wave is modeled to determine the amplitude of the magnetic perturbation. If we assume that these waves are continuously generated in all directions then the wave energy flux is 1.6 × 10 19 W; for comparison, the kinetic energy flux of the solar wind at 1AU is 1.7 × 10 20 W. With better technology and the maturity of 3D tomography, the solar radioscience community is experiencing a resurgence of interest in the phenomenon of Faraday rotation. This thesis demonstrates that Faraday rotation can be used to determine the magnetic structure of CMEs, the solar wind, and MHD waves propagating from the solar corona. These observations enable us to predict the geoeffectiveness of a CME, study force balance in the solar wind, and measure magnetic energy flux in important regions such as the solar wind acceleration region.

本数据集源自伊丽莎白·A·延森（Elizabeth A. Jensen）2007年发表的博士论文，内含多个附录。附录F包含用于分析的原始射频数据光盘与MATLAB处理代码。附录C包含通过差分距离与积分多普勒（Differenced Range Versus Integrated Doppler）方法在部分观测时段采集的总电子含量数据。观测所用接收天线阵列位于美国加利福尼亚州戈德斯通的深空网（Deep Space Network）。

手稿来源：Proquest学位论文库2007年版，第0031部分第0606节，共264页；[哲学博士学位论文]。美国加利福尼亚州：加利福尼亚大学洛杉矶分校；2007年。出版物编号：AAT 3268543。来源：DAI-B 68/06，2007年12月。https://ui.adsabs.harvard.edu/abs/2007PhDT.........4J/abstract

摘要：温度达百万摄氏度的太阳日冕会产生太阳风，进而调控地球的“空间天气”。0.25天文单位（AU，即60倍太阳半径）范围内的日冕磁场对太阳风加速起到关键作用，但该磁场基本处于“不可见”状态，目前仅能通过高频电磁波的法拉第旋转（Faraday rotation）进行测量。法拉第旋转指电磁波穿过磁化介质时，其偏振平面发生的可观测旋转现象。观测到的法拉第旋转量，是沿电磁波传播方向，对平行于传播矢量的磁场分量与电子密度的乘积进行积分得到的结果。法拉第旋转可有效用于日冕磁场测量。作为一种遥感观测手段，法拉第旋转测量在分析过程中需要对传播介质进行细致考量。

本论文详细阐述了法拉第旋转的理论基础、此前利用处于上合位置的航天器载波信号开展的法拉第旋转观测实验、卡西尼号（Cassini）法拉第旋转观测所用设备、从射频数据中提取法拉第旋转观测结果所需的信号分析流程与操作步骤、用于拟合观测数据的模型，以及上述流程所需的全部辅助数据与相关代码。本论文所用数据与代码均存储于随附的DVD光盘中。

此前所有法拉第旋转观测实验均针对产生“W”形或S形特征的日冕物质抛射（Coronal Mass Ejection, CME）。本文采用泰勒态磁通绳模型，令其以不同尺寸、扭缠度与方位角穿过视线方向，重现了上述观测结果，证明法拉第旋转可用于测量日冕物质抛射的磁场。

本研究采用正向模型拟合法拉第旋转与柱积分电子密度观测数据，对太阳日冕中的力平衡开展了一阶分析。通过上述拟合结果，我们计算得到了磁场压强、热压强的梯度以及单位体积的引力。若要让太阳风脱离太阳引力束缚，磁场与热压强的梯度必须占据主导地位。我们通过2002年6月20日的拟合结果证明，对势场源表面模型（Potential Field Source Surface, PFSS）进行小幅调整，即可提供太阳风流动所需的磁场强度以满足压强需求；但2002年6月21日的拟合结果则无法满足这一条件。6月21日的观测最接近点均位于2.5倍太阳半径的源表面下方，这表明利用势场源表面模型确定源表面以下的日冕磁场结构存在局限性。

赫利俄斯号（Helios）与卡西尼号的法拉第旋转观测中均观测到了周期为4分钟的大振幅阿尔文波（Alfvén wave）。我们采用可传播磁流体动力学（Magnetohydrodynamics, MHD）波的开放式箱体模型，证明法拉第旋转与柱积分电子密度观测数据的组合可区分阿尔文波：这是因为阿尔文波不存在流体扰动。我们同时证明，法拉第旋转观测中的二次谐波源于磁流体动力学磁声（快、慢）模中的电子密度涨落。这表明此前赫利俄斯号观测到的二次谐波实为磁流体动力学磁声波。

我们对卡西尼号观测到的阿尔文波进行建模，以确定磁扰动的振幅。若假设这些波在所有方向上持续产生，则其波能通量为1.6×10^19 W；作为对比，1天文单位（AU）处太阳风的动能通量为1.7×10^20 W。

随着技术进步与三维断层成像技术的成熟，太阳射电科学学界对法拉第旋转现象的研究兴趣再度复苏。本论文证明，法拉第旋转可用于确定日冕物质抛射、太阳风以及从太阳日冕传播而出的磁流体动力学波的磁场结构。此类观测可帮助我们预测日冕物质抛射的地球效应、研究太阳风中的力平衡，并测量太阳风加速区域等重要区域的磁能通量。