Earth's Electromagnetic Environment: Advancing Recent Discoveries in Auroral Plasma Radio Emission Research

在距地面70英里以上，近地环境(地球空间)主要由地球磁场组成，在更远的距离上，磁场与太阳风(带电粒子、等离子体，从太阳以极快的速度流动)和行星际磁场(扩展的太阳磁场)相互作用。地球空间主要由起源于大气或太阳风的等离子体组成。这两个主要参与者--磁场和带电粒子--的相互作用具有各种形式，并产生许多有趣的电磁现象，如极光(北极光和南极光)、等离子体波、自然电磁辐射和电流等，特别是在这种相互作用最强烈并到达地球附近的极地地区。研究这些现象很重要，因为它们影响卫星仪器和通信，以及GPS(全球定位系统)等重要技术。一项以前由美国国家科学基金会资助、最近几年在南极洲进行的研究工作取得了与极地地区自然电磁现象有关的新发现。这些发现是：(1)在地球上空约200,000公里处观测到的强大的极光千米辐射与在南极站同时观测到的类似信号之间的关联；(2)发现了电子回旋频率(带电粒子在磁场中振荡的一个重要频率)高次谐波的辐射；(3)发现了一种源于极光的新型射电发射。这些现象最容易观察到，而且大多数情况下只能使用部署在人为电磁干扰最小的南极洲的仪器来观察。基于这些发现的新研究将极大地促进我们对地球自然电磁环境的了解，这反过来又对更广泛的地球空间环境和空间天气产生重大影响，因为这些系统是如何相互关联的。此外，这项研究探索的新发现代表了地球空间研究的突出问题，这些问题到目前为止还没有引起科学家的注意。这项研究是一项具有成本效益的投资，将促进地球航天领域的知识状况，并为达特茅斯学院的学生提供一个在实验测量和数据分析方面获得良好技能和经验的机会。

Above 70 miles over the ground, the near-Earth's environment (Geospace) is mostly organized by the Earth's magnetic field, which at a greater distance interacts with the solar wind (charged particles, plasma, flowing with a great speed from the Sun) and interplanetary magnetic field (extended Sun's magnetic field). Geospace is mostly populated by plasma that originates either in the atmosphere or in the solar wind. Interaction of the these two major players - magnetic fields and charged particles - takes various forms and produces many interesting electromagnetic phenomena such as aurorae (Northern and Southern lights), plasma waves, natural electromagnetic radiation and currents, etc., especially in the polar areas where this interaction is most intense and reaches close to the Earth. Studying these phenomena is important since they affect satellite instrumentation and communication, as well as important technologies such as GPS (Global Positioning System). A research effort previously funded by NSF and performed in Antarctica within the last few years made new discoveries related to natural electromagnetic phenomena in the polar areas. These discoveries are: (1) correlations between powerful auroral kilometric radiation observed at ~200,000 km above the Earth and analogous signals observed simultaneously at the South Pole Station; (2) discovery of radiation at a high harmonic of the electron cyclotron frequency (an important frequency at which charged particles oscillate in a magnetic field); and (3) discovery of a new type of radio emission of auroral origin. These phenomena are best observed, and in most cases can only be observed, using instruments deployed in Antarctica where a manmade electromagnetic interference is minimal.The new research built on these discoveries will significantly advance our knowledge of the Earth's natural electromagnetic environment, which in turn has significant impact on the broader Geospace environment and space weather because of how interconnected these systems are. Furthermore, the new discoveries probed by this research represent outstanding questions of Geospace research that have escaped scientists' attention so far. The research is a cost-effective investment that will advance the state of knowledge of the Geospace domain and provide students at Dartmouth College with an opportunity to obtain good skills and experience with experimental measurements and data analysis.