Current Systems around Terrestrial Planets: EOF Analysis and Modeling

行星的磁层由许多因素控制，如本征磁场、大气层和电离层以及太阳风。这些控制因素的不同组合在水星、金星、地球和火星上起作用，因此它们形成了一套非常适合进行定量比较研究的集合。只有地球和水星上存在显著的本征偶极磁场。然而，水星的形态与地球有很大的不同，因为水星不支持大气层和电离层，偶极场要弱得多，太阳风更密集，而行星际磁场更强。火星和金星都有大气层，但缺乏全球行星磁场，火星上存在区域地壳磁化。这项建议旨在利用金星快车、火星全球探测器、CHAMP(地球)和信使(水星)等轨道航天器收集的磁矢量数据，调查和比较类地行星空间环境中的电流系统。我们建议构建数据驱动的和物理上有意义的表示，以揭示和量化各种控制因素的影响。为了实现这一点，我们将根据行星磁场观测的具体情况定制经验正交函数(EOF)分析和其他多变量方法。与建立在预定义函数(如球谐函数)上的表示法不同，EOF方法中的基函数直接从数据中推导出来。EOFs被设计成提取主要的相干变化，以便根据已知的物理现象进一步解释，然后在回归步骤中，使用合适的控制变量进行建模。因此，EOF方法可以单独量化每个行星的控制因素的相对重要性，从而有助于解决热门的科学问题。由此产生的经验模型将促进对类地行星当前系统的比较研究。

The magnetosphere of a planet is controlled by a number of factors such as the intrinsic magnetic field, the atmosphere and ionosphere, and the solar wind. Different combinations of these control factors are at work at the terrestrial planets Mercury, Venus, Earth, and Mars, hence they form a very suitable set for quantitative comparative studies. A significant intrinsic dipolar magnetic field is present only on Earth and on Mercury. However, the configuration at Mercury differs considerably from that at Earth because Mercury does not support an atmosphere and ionosphere, the dipolar field is much weaker, the solar wind denser, and the interplanetary magnetic field stronger. Both Mars and Venus have atmospheres but lack a global planetary magnetic field, with regional crustal magnetization being present on Mars. This proposal aims at investigating and comparing electrical current systems in the space environments of terrestrial planets using magnetic vector data collected by orbiting spacecraft such as Venus Express, Mars Global Surveyor, CHAMP (Earth), and MESSENGER (Mercury). We propose to construct data-driven and physically meaningful representations that reveal and quantify the influence of various control factors. To achieve this, we will tailor Empirical Orthogonal Function (EOF) analysis and other multivariate methods to the specifics of planetary magnetic field observations. In contrast to representations that build on predefined functions like spherical harmonics, basis functions in the EOF approach are derived directly from the data. EOFs are designed to extract dominant coherent variations for further interpretation in terms of known physical phenomena, and then, in a regression step, for modeling using suitable control variables. The EOF methodology thus allows quantifying the relative importance of control factors for each planet individually, and thus contributes to the solution of topical science questions. The resulting empirical models will facilitate comparative studies of current systems at the terrestrial planets.