Collaborative Research: GEM--The Excitation and Propagation of Fast Magnetosonic Waves and Their Effect on Radiation Belt Electrons

合作研究：GEM--快磁声波的激发和传播及其对辐射带电子的影响

• 批准号: 1602388
• 负责人: Kyungguk Min
• 金额: $ 29.74万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1602388&HistoricalAwards=false
• 关键词: Collaborative; Research; GEM; Excitation; Propagation

This project will investigate the generation, propagation and dissipation of magnetosonic waves in the inner region of the magnetosphere as well as the energization of radiation belt electrons interacting with them. In the space environment near Earth, the plasma is so tenuous that plasma particles (ions and electrons) rarely collide. However despite this, some portion of the electrons in the magnetosphere reach dangerously high energies exceeding a million electron volts. This energy is high enough to pose a risk to satellites orbiting within the inner regions of the magnetosphere, a preferred location for communications, navigation, search-and-rescue, weather prediction and national security satellites. Plasma waves are mainly responsible for the acceleration of radiation belt electrons to these high energies but they can also contribute to the scattering of radiation belt particles into the Earth's atmosphere. Many types of plasma waves are generated in a collisionless plasma in the presence of a magnetic field and each has its own set of interactions with the charged particles in the plasma. These waves play a significant role in the dynamics of the inner magnetosphere and radiation belts. Magnetosonic waves, the focus of the proposed investigation, are found in the vicinity of the magnetic equatorial plane in a wide region near the dayside portion of the magnetosphere. The component of the wave electric field, which is aligned along a magnetic field line, can continuously accelerate electrons traveling near the speed of the wave in much the same way that a surfer is pushed forward by an ocean wave. This is termed Landau damping. Magnetosonic waves are thought to be generated by ring current protons, and dissipated in accelerating radiation belt electrons, in effect acting as intermediaries in the collisionless transport of energy between different particle populations. As a broader impact, this project is led by an early-career scientist thus contributing to the training of the next generation of scientists. The primary goal of this research is to use linear theory and kinetic particle-in-cell (PIC) simulations to explore the excitation and propagation of fast magnetosonic waves driven by observed types of ring-like proton velocity distributions and to use insights gathered to interpret the observed wave measurements, both datasets from the twin Van Allen Probes. Furthermore, scattering of radiation belt electrons will be quantified using test-particle computations, providing clear criteria as to whether and under what conditions the conventional quasi-linear approach can be applied. Two fundamental science questions will be addressed: (1) how does the excitation and propagation of fast magnetosonic waves produce the complex pattern of the observed wave frequency spectra? and (2) how important to the evaluation of radiation belt electron scattering are the complex kinetic dispersion properties of the waves compared to the commonly assumed cold plasma dispersion used in quasi-linear theory? The generalization of the full kinetic PIC code to account for the dipole magnetic field in an inhomogeneous medium will be an additional valuable resource for the radiation belt community enabling a whole spectrum of new studies not previously possible.

本项目将研究磁声波在磁层内部的产生、传播和耗散，以及与磁声波相互作用的辐射带电子的能量。在地球附近的空间环境中，等离子体非常脆弱，等离子体粒子（离子和电子）很少发生碰撞。然而，尽管如此，磁层中的某些电子达到了危险的高能量，超过了一百万电子伏特。这种能量高到足以对在磁层内部区域运行的卫星构成威胁，而磁层内部区域是通信、导航、搜救、天气预报和国家安全卫星的首选位置。等离子体波主要负责辐射带电子加速到这些高能量，但它们也可以促进辐射带粒子散射到地球大气中。许多类型的等离子体波是在磁场存在的无碰撞等离子体中产生的，每种波都与等离子体中的带电粒子有自己的一套相互作用。这些波在内磁层和辐射带的动力学中起着重要的作用。磁声波是本次研究的重点，它存在于磁赤道面附近的一大片区域内，靠近磁层的日侧部分。波电场的组成部分沿着磁场线排列，可以不断地加速电子在接近波的速度下运动，就像冲浪者被海浪推动一样。这被称为朗道阻尼。磁声波被认为是由环电流质子产生的，并在加速辐射带电子中消散，实际上充当了不同粒子群之间无碰撞能量传输的中介。作为一个更广泛的影响，该项目由一位早期职业科学家领导，从而有助于培养下一代科学家。本研究的主要目标是利用线性理论和动力学粒子池（PIC）模拟来探索由观测到的环状质子速度分布驱动的快速磁声波的激发和传播，并利用收集到的见解来解释观测到的波测量，这两个数据集都来自双范艾伦探测器。此外，辐射带电子的散射将使用测试粒子计算来量化，为是否以及在什么条件下可以应用传统的准线性方法提供明确的标准。将解决两个基本科学问题：(1)快速磁声波的激发和传播如何产生观测到的波频谱的复杂模式？(2)与准线性理论中通常假设的冷等离子体色散相比，波的复杂动力学色散特性对辐射带电子散射的评价有多重要？推广完整的动力学PIC代码来解释非均匀介质中的偶极子磁场，将是辐射带界的一个额外的宝贵资源，可以实现以前不可能实现的全谱新研究。