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如何驱动地球附近的空间天气扰动。地球受到磁场的保护，使其不受太阳风的直接影响，磁场延伸到高海拔，使太阳风绕着地球偏转。当地球上的S磁场通过一种叫做磁合并的过程与太阳的磁场相连时，一些太阳风能就进入了近地空间。太阳风和地球磁层之间的相互作用会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高能量，此外，还会在高层大气中产生兆安电流，从而扰乱地球表面的电网。为了预测空间天气，从而为实施调解战略提供一些警告，重要的是了解太阳风中实际击中磁层的条件。复杂的情况出现了，因为为了获得足够的提前时间使预测具有价值，太阳风必须在地球上游进行测量。然而，这种不受干扰的太阳风并不是最终触发太空风暴的原因。相反，太阳风在到达磁层之前会被修改，形成弓形激波和一层被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远处未受干扰的太阳风的观测与实际到达的太阳风联系起来，然后与产生的空间风暴联系起来。这项研究的结果将用于研究生和本科教育，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进空间气象预报，对社会有价值，并将与行星和天体物理等离子环境的研究有关。相关的空间气象主题将在各场馆的公共宣传活动中亮相。与地球物理研究所公共信息和外展教育办公室的合作将大大扩大推广活动的范围，使其不再局限于提议的团队。观测表明，一群太阳风离子从弓激波反射，向太阳返回，并与即将到来的太阳风非线性相互作用，产生各种在弓激波上游的瞬变特征(即热流异常、前震空洞和密度洞)。虽然这些瞬变已经观测了几十年，但产生它们的基本物理机制，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信号类型，仍然不清楚。由于太阳风与磁层的相互作用产生瞬变，而瞬变又反馈到修改太阳风-磁层的相互作用，因此必须将这些特征作为一个相互关联的系统来研究，以确定潜在的机制。目前的工作将使用观测来确定各种类型的太阳风瞬变，以及它们产生的条件，然后使用模拟来确定潜在的物理机制。这种全面的方法预计将产生重要的进展。