CAREER: Kinetic Phenomena Upstream from the Earth's Bow Shock and Their Geomagnetic Effects

职业：地球弓形激波上游的动力学现象及其地磁效应

• 批准号: 1352669
• 负责人: Hui Zhang
• 金额: $ 65.06万
• 依托单位: University of Alaska Fairbanks Campus
• 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: 2015-07-15 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1352669&HistoricalAwards=false
• 关键词: CAREER; Kinetic; Phenomena; Upstream; Earth

This project is focused on better understanding of the ways in which solar wind energy drives space weather disturbances near Earth. The Earth is protected from the direct impact of the solar wind by its magnetic field that extends out to high altitudes and causes the solar wind to be deflected around it. When the Earth?s magnetic field becomes connected to the Sun's magnetic field through a process called magnetic merging, some of the solar wind energy enters near-Earth space. The interaction between the solar wind and the Earth's magnetosphere accelerates plasma particles to energies high enough to threaten spacecraft electronics and astronaut health, and in addition, creates mega-ampere electric currents in the upper atmosphere that can disrupt power grids on the Earth's surface. To predict space weather and thus provide some warning to implement mediation strategies, it is important to understand the conditions in the solar wind that actually hit the magnetosphere. Complications arise because to get sufficient lead-time for the prediction to be of value, the solar wind must be measured upstream of the Earth. However, this undisturbed solar wind is not what eventually triggers the space storming. Instead the solar wind is modified as it forms a bow shock and a layer of shocked and heated plasma (called the magnetosheath) before arriving at the magnetosphere. As a result, it is important to be able to relate observations of the undisturbed solar wind far upstream of the Earth with the solar wind that actually arrives and then to the space storm that is produced. The results of this study will be used for graduate and undergraduate education purposes, and will be disseminated widely. Taking a longer-range perspective, a better understanding of the solar wind-magnetosphere interaction will likely result in improvements to space weather forecasting of value to society and will be relevant to the study of planetary and astrophysical plasma environments. Related space weather topics will be featured in public outreach activities in various venues. A partnership with the Public Information and Outreach Education Office at the Geophysical Institute will significantly increase the scope of the outreach activities beyond the proposing team alone.Observations indicate that a population of solar wind ions reflects from the bow shock, travels back toward the Sun and interacts non-linearly with the incoming solar wind producing a variety of transient features (i.e., hot flow anomalies, foreshock cavitons, and density holes) upstream of the bow shock. Though these transients have been observed for decades, the underlying physical mechanisms that produce them, how they modify the solar wind-magnetosphere interaction, and the types of signatures that result within near-Earth space are still not understood. Since the interaction of the solar wind with the magnetosphere produces the transients and the transients feed back to modify the solar wind-magnetosphere interaction, these features must be studies as a connected system in order to identify the underlying mechanisms. The present work will use observations to identify the various types of solar wind transients, and the conditions under which they are produced, and then use simulations to identify the underlying physical mechanisms. This holistic approach is expected to produce important advances.

该项目的重点是更好地了解太阳风能驱动地球附近空间天气扰动的方式。地球的磁场延伸到高空，导致太阳风在地球周围偏转，从而保护地球免受太阳风的直接影响。当地球磁场通过磁合并过程与太阳磁场相连时，一些太阳风能就会进入近地空间。 太阳风和地球磁层之间的相互作用将等离子体粒子加速到足以威胁航天器电子设备和宇航员健康的能量，此外，还会在高层大气中产生兆安级电流，从而破坏地球表面的电网。 为了预测太空天气并为实施调解策略提供一些警告，了解实际撞击磁层的太阳风的条件非常重要。 复杂性的出现是因为为了获得足够的提前时间以使预测有价值，必须在地球上游测量太阳风。 然而，这种未受干扰的太阳风并不是最终引发太空风暴的原因。 相反，太阳风在到达磁层之前会发生改变，因为它会形成弓形激波和一层受到冲击和加热的等离子体（称为磁鞘）。 因此，重要的是能够将对地球上游未受干扰的太阳风的观测与实际到达的太阳风以及随后产生的太空风暴联系起来。 这项研究的结果将用于研究生和本科生教育，并将广泛传播。 从更长远的角度来看，更好地了解太阳风-磁层相互作用可能会改善对社会有价值的空间天气预报，并将与行星和天体物理等离子体环境的研究相关。 相关空间天气主题将在各个场馆的公共宣传活动中进行专题介绍。 与地球物理研究所公共信息和外展教育办公室的合作将显着扩大外展活动的范围，而不仅仅是提议团队。观察表明，太阳风离子群从弓形激波反射，返回太阳并与入射的太阳风非线性相互作用，在弓激波上游产生各种瞬态特征（即热流异常、前震空穴和密度空洞）。 尽管这些瞬变现象已经被观测了几十年，但产生它们的潜在物理机制、它们如何改变太阳风-磁层相互作用以及在近地空间内产生的特征类型仍然不清楚。由于太阳风与磁层的相互作用会产生瞬变，并且瞬变反馈会改变太阳风-磁层的相互作用，因此必须将这些特征作为一个连接系统进行研究，以便识别潜在的机制。 目前的工作将利用观测来识别各种类型的太阳风瞬变及其产生的条件，然后利用模拟来确定潜在的物理机制。这种整体方法预计将产生重要进展。