Collaborative Research: GEM: Propagation and Dissipation of Electromagnetic Ion Cyclotron Waves in the Magnetosphere and Ionosphere

地球磁层中有多种类型的等离子体波。几十年来，人们已经观察到在接近离子回旋频率的Pc1-2频率范围(0.1-5 Hz)的超低频电磁离子回旋(EMIC)波是磁层-电离层系统的一个显著特征。这些波在将电离层离子加热到磁层能量、调节磁层中的压力各向异性、在亚暴期间用高能重离子填充磁层以及诱导质子增强方面发挥着重要作用。已知激磁波在内部磁层的磁赤道附近以左手极化波的形式被激发，然后到达地面，沿着磁力线传播。高频EMIC波在向地面传播的过程中通常会被过滤，而低频EMIC波可以有效地到达地面。理解这一现象是复杂的，因为EMIC波可能受到各种物理过程、磁层/电离层中沿传播路径的等离子体环境以及波特性的影响。该团队建议使用模型以及空间和地面观测来更好地了解EMIC波的传播和消散。这个合作研究项目由来自四个研究所的科学家组成，其中包括两个非R1学院。这个项目旨在通过回答以下四个科学问题来研究EMIC波在磁层和电离层中的传播和耗散：1.EMIC波是如何到达地面的？2.EMIC波的传播是如何受到地磁活动的影响的？3.地磁场的拓扑结构，如压缩和拉伸磁场，如何影响波的传播？4.在上述参数的背景下，EMIC波的极化有什么意义？波的极化与传播有何关系？该团队将使用最先进的全波模拟程序Petra-M，该程序使用有限元方法。使用有限元方法的一个优点是，在模拟程序中可以很容易地采用各种磁场拓扑和背景等离子体参数。Petra-M代码将利用真实的地球磁场拓扑(偶极磁场和压缩磁场)和来自经验密度模型的密度配置。将进行波浪模拟以检查波浪的产生和传播。该团队还将分析多颗卫星最近对这些波的观测，并将它们与地面磁力计网络的观测结果进行比较。为了考虑电磁波在内磁层中的传播，作者将研究空间(GOES卫星)与地面之间的EMIC波事件的以下特征，空间分布(L和MLT)，与太阳和地磁活动的关系，GOS卫星到等离子体顶层位置的距离，以及波的特性，如极化、频率和法向角。对于外部磁层中的EMIC波，该小组还将使用高纬度地面站调查空间(MMS、THEMIS和星系团)-地面共轭观测。这一奖项反映了NSF的法定任务，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

There are many types of plasma waves in the Earth's magnetosphere. For decades it has been observed that ultra-low frequency electromagnetic ion cyclotron (EMIC) waves in the Pc 1-2 frequency range (0.1-5 Hz) near the ion cyclotron frequency are a prominent feature of the magnetosphere-ionosphere system. These waves play an important role in heating ionospheric ions to magnetospheric energies, regulating pressure anisotropy in the magnetosphere, populating the magnetosphere with energetic heavy ions during substorms, and inducing enhanced protons. EMIC waves are known to be excited as left-hand polarized waves near the magnetic equator in the inner magnetosphere and reach the ground propagating along the magnetic field line. Higher-frequency EMIC waves are often filtered during wave propagation to the ground, while lower-frequency EMIC waves can effectively reach the ground. Understanding this phenomenon is complicated because EMIC waves can be affected by various physical processes, the plasma environment along the propagation path in the magnetosphere/ionosphere, and wave properties. The team proposed to understand better the propagation and dissipation of EMIC waves using models and both space and ground-based observations. This collaborative research project consists of scientists from four institutes, including two non-R1 colleges. This project aims to investigate the propagation and dissipation of EMIC waves in the magnetosphere and ionosphere by answering these four scientific questions: 1. How do EMIC waves reach the ground?2. How is EMIC wave propagation affected by geomagnetic activity?3. How does geomagnetic field topology, such as compressed and stretched magnetic field, affect wave propagation?4. What is the significance of EMIC wave polarization in the context of the above parameters and how are wave polarizations related with propagation?The team will employ a state-of-art full-wave simulation code, Petra-M, which uses the finite element method (FEM). One advantage of using the FEM is that various magnetic field topologies and background plasma parameters are easily adopted in the simulation code. The Petra-M code will utilize realistic terrestrial magnetic field topologies (dipole and compressed magnetic field) and density configurations from empirical density models. Wave simulations will be performed to examine wave generation and propagation. The team will also analyze recent observations of these waves by multiple satellites and compare them with the ground magnetometer network observations. To consider the EMIC wave propagation in the inner magnetosphere, the proposers will investigate the following characteristics of the EMIC wave events between space (GOES satellite) and ground, spatial distribution (L and MLT), relationship with solar and geomagnetic activity, the distance between GOES satellites and plasmapause locations, and wave properties such as polarization, frequency, and normal angle. For the EMIC waves in the outer magnetosphere, the team will also investigate space (MMS, THEMIS, and Cluster)-ground conjugate observations using high-latitude ground stations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.