GEM: Experimental Identification of Plasma Wave Modes in Vicinity of KH Vortices and in Plasma 'Mixing' Regions in Low Latitude Boundary Layer

GEM：KH 涡旋附近和低纬边界层等离子体“混合”区域等离子体波模式的实验识别

• 批准号: 1502774
• 负责人: Katariina Nykyri
• 金额: $ 17.97万
• 依托单位: Embry-Riddle Aeronautical University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-15 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1502774&HistoricalAwards=false
• 关键词: GEM; Experimental; Identification; Plasma; Wave

Space is not empty but is filled with energetic electrons and ions that blow outward from the Sun carrying with them solar magnetic field lines. The dangerous levels of energy and momentum, contained in this medium, constantly bombard the Earth. Though the Earth's magnetic field acts as a shield deflecting most of this medium around the Earth, some small fraction makes its way through the Earth's magnetic shield (called the magnetopause) and, even this small amount can power space storms at high altitudes in the space surrounding the Earth. How this happens is an important problem because severe space storms can negatively impact a variety of technologies upon which our interconnected society relies. Most recently, the potential of extreme space weather events to disrupt power grids over global scales with cascading disruption of a large variety of critical social infrastructures has been the subject of national and international attention. It is commonly accepted that primary mechanism to deliver solar wind energy into the magnetosphere is the joining of the Earth's magnetic field lines with the Sun's through the process of magnetic merging. However, another route has recently come to light though the exact details and relative importance are not yet known. Large amplitude low frequency plasma waves are commonly observed just inside the magnetopause in the vicinity of mixed populations of heated and cold ions and Kelvin-Helmholtz waves. Kelvin-Helmholtz waves are waves generated on the magnetopause surface by the solar wind blowing past. Current theories suggest that these surface waves couple to internal waves along magnetic field lines (called kinetic Alfven waves) at the plasma and field gradients associated with the magnetopause. These waves are able to heat ions within the magnetosphere. This process, in effect, transmits energy from the solar wind into the ion populations within the magnetosphere. However, there has been no experimental confirmation yet that the observed low frequency waves in this region are indeed kinetic Alfven waves. This proposal introduces a novel data analysis technique that is able to identify the modes of the observed plasma waves. If successful this represents a major step forward. The science topic addressed here has parallels with the problem of solar coronal heating; therefore advances will also be of interest to the solar and astrophysics communities. A graduate student will receive training and mentoring while working on this project and undergraduate REU students will participate in the project over the summer months. Finally the PI is herself an early career female physics professor who will be able to continue her research program at Embry-Riddle Aeronautical University as a result of this project.This project uses a newly demonstrated novel technique to experimentally determine the dispersion relation and thus identify the wave modes of large-amplitude plasma waves frequently present in the low latitude boundary layer. This technique requires two Cluster spacecraft with the appropriate separation to observe a plasma wave in a region of mixed plasma populations or K-H waves in the vicinity of the magnetopause. Observations of electric and magnetic fields by the two spacecraft are used in the construction of the dispersion relation, which allows identification of the particular plasma wave mode. The technique has been successfully for one case. Identifying a significant number of such events where the above conditions are met introduces considerable risk into the success of the project but if successful, the rewards are high.

太空并非空空如也，而是充满了高能电子和离子，它们从太阳向外吹来，携带着太阳磁力线。这种介质所包含的危险的能量和动量，不断地轰击着地球。虽然地球的磁场起着屏蔽作用，使地球周围的大部分介质偏转，但仍有一小部分通过地球的磁屏蔽（称为磁层顶），即使是这一小部分也可以为地球周围高海拔空间的太空风暴提供动力。这是如何发生的是一个重要的问题，因为严重的太空风暴会对我们相互联系的社会所依赖的各种技术产生负面影响。最近，极端空间天气事件对全球范围内电网的潜在破坏，以及对各种关键社会基础设施的连锁破坏，一直是国家和国际关注的主题。人们普遍认为，将太阳风能量传递到磁层的主要机制是通过磁合并过程将地球的磁力线与太阳的磁力线连接起来。然而，另一条路线最近浮出水面，尽管具体细节和相对重要性尚不清楚。大振幅低频等离子体波通常在磁层顶内的冷热离子混合种群和开尔文-亥姆霍兹波附近被观察到。开尔文-亥姆霍兹波是太阳风吹过时在磁层顶表面产生的波。目前的理论认为，这些表面波在等离子体和与磁层顶相关的场梯度处沿磁场线（称为动态阿尔芬波）与内部波耦合。这些波能够加热磁层内的离子。实际上，这个过程将太阳风的能量传递到磁层内的离子群中。然而，目前还没有实验证实在该区域观测到的低频波确实是动力学阿尔芬波。本文提出了一种新的数据分析技术，该技术能够识别观测到的等离子体波的模式。如果成功，这将是向前迈出的一大步。这里讨论的科学主题与太阳日冕加热问题有相似之处；因此，太阳和天体物理学团体也会对这些进展感兴趣。研究生将接受培训和指导，同时在这个项目中工作，本科REU学生将在夏季参加这个项目。最后，PI本人也是一名早期职业女性物理学教授，由于这个项目，她将能够在安柏瑞德航空大学继续她的研究项目。本项目采用一种新证明的新技术，通过实验确定色散关系，从而确定在低纬度边界层中频繁出现的大振幅等离子体波的波模。这项技术需要两个具有适当间隔的Cluster航天器来观测混合等离子体种群区域的等离子体波或磁层顶附近的K-H波。两个航天器对电场和磁场的观测用于构建色散关系，从而可以识别特定的等离子体波模式。该技术在一个案例中取得了成功。在满足上述条件的情况下，确定大量此类事件会给项目的成功带来相当大的风险，但如果成功，则回报很高。