Turbulent Ion Heating in the Magnetosheath

地球的磁场将它包裹在一个被称为磁层的保护性茧中，使其周围的大部分太阳风偏转。太阳风是一股带电粒子流，离子和电子的数量大致相等，以及从太阳向外吹来的磁场，其强度随太阳活动而变化。太阳风移动得如此之快，以至于当它遇到磁层时，就会在其上游形成冲击波。当太阳风等离子体穿过激波时，它会减慢速度，然后在被称为磁鞘的鞘区域内围绕磁层流动。在这个区域，磁场是不稳定的或湍流的，有证据表明，当湍流消散时，磁鞘离子会被加热。这个话题之所以引人注目，是因为湍流和相关的离子加热的潜在重要性直到最近才被认识到。磁鞘中的离子最终穿过磁层顶，提供磁层等离子体的主要来源，因此，它们的温度和其他性质的变化可以对磁层本身的稳定性产生深远的影响，这可能导致在地磁风暴和亚暴期间爆炸式的能量释放。这项研究的方法是创造性的，与以前的研究相比是一项重要的进步，因为这是第一次对这种湍流及其消散进行自我协调的全面处理。因此，新发现的可能性很高。认识的进步将使社会受益，因为从长远来看，它们将有助于改进预测能力，可用于将此类事件的影响降至最低。这项研究通过培养一名博士后和一名研究生，为发展一支科学队伍做出了贡献。研究成果将通过出版物、会议和社区外展进行传播。为了实现其目标，本研究调查了Alfvenic湍流如何加热磁鞘离子，加热过程如何饱和，能量传递到离子的速率，电磁能量如何传输以支持加热过程，加热过程中二次波发射如何发展，以及加热过程如何影响磁鞘等离子体的整体特性。主要工具是细胞模型中的3D混合粒子。该方案使用THEMIS卫星观测到的波/离子加热事件来指定初始条件并验证模拟结果。一个创新的方面是耦合处理与等离子体湍流相关的级联过程和由于离子分布中发展的各向异性而产生的附加不稳定性。

Earth's magnetic field encloses it in a protective cocoon, called the magnetosphere, deflecting most of the solar wind around it. The solar wind is a stream of charged particles, approximately equal numbers of ions and electrons, and magnetic fields blowing outward from the Sun, which varies in intensity with solar activity. The solar wind moves so fast that when it encounters the magnetosphere a shock forms upstream from it. As solar wind plasma passes through the shock it is slowed down and then flows around the magnetosphere in a sheath region, called the magnetosheath. In this region the magnetic field is erratic or turbulent and evidence suggests that magnetosheath ions are heated as this turbulence is dissipated. The topic is compelling because the potential importance of turbulence and associated ion heating has only recently been recognized. Ions in the magnetosheath eventually cross the magnetopause to provide the dominant source of magnetospheric plasmas, thus changes in their temperature and other properties can have a profound effect on the stability of the magnetosphere itself, which can lead to explosive releases of energy during geomagnetic storms and substorms. The methodology for this study is creative and an important advance over previous studies because it is the first self-consistent comprehensive treatment of this turbulence and its dissipation. As such, the potential for new discoveries is high. Advances in understanding will have benefit to society because, in the longer term, they will contribute to the development of an improved predictive capability that can be used to minimize the impacts of such events. This research contributes to the development of a scientific workforce by training a postdoctoral student and a graduate student. Research results will be disseminated through publications, conferences, and community outreach.In order to fulfill its objectives, this study investigate how Alfvenic turbulence heats magnetosheath ions, how the heating process saturates, the rate at which energy is transferred to the ions, how electromagnetic energy is transported to support the heating process, how secondary wave emissions develop during the heating, and how the heating process influences the bulk characteristics of the magnetosheath plasma. The primary tool is a 3D hybrid particle in cell model. The proposal uses wave/ion heating events observed by the THEMIS satellites to both specify initial conditions and to validate simulation results. An innovative aspect is the coupled treatment of both the cascade processes associated with plasma turbulence and the additional instabilities that arise from the anisotropies that develop in the ion distributions.