Cusp Turbulence and Transport and their Impact on Ionospheric Coupling

受冲击的太阳风等离子体或磁鞘为地球磁层提供了基本的输入和外部边界条件。磁鞘等离子体进入磁层和电离层的最直接通道发生在外极尖区域。因此，加强对磁鞘/尖端界面等离子体过程的理解对于推进磁层顶和边界层物理学至关重要。由于外磁层边界附近的磁场向尾部弯曲，整个磁层边界层通过这一尖端区域被映射到接近局地正午的正面高纬度电离层。虽然等离子体和外尖场的相互作用在磁鞘和边界层与电离层的联系中起着关键作用，但在该地区很少有卫星测量。该项目的目标是通过关注等离子体和动量输运、场波动以及由此产生的尖端电流系统，推进对外层和中海拔极尖的等离子体、场和等离子体波相互作用的认识。研究人员将确定和测试那些与增强卫星独特观测最相关的等离子体和场的相互作用，并将其用作外尖端和中高度尖端地区粒子和场特征的基线样本。尽管非常有限，但在外层尖端的现有观测提供了足够的总体几何和等离子体条件信息，可以应用最先进的二维MHD和磁鞘-尖端相互作用区域的混合模拟，包括与电离层的耦合。这样的模拟将提供有关局地随时间的流动和磁场的信息，以及更非局地的尖峰/电离层电流系统。了解异常的跨场动量输运对于建立尖端和日侧电流系统的定量模型至关重要。因此，pi将关注剪切流驱动的不稳定性以及相关的湍流和输送。将完成通过磁鞘/外尖和中海拔尖壁边界的剪切流的逼真的二维和三维混合模拟。将比较电和磁波动谱的理论预测，特别是与观测到的极低频波谱。然后，将根据观测到的波动谱计算跨场输运，以评估尖峰区域异常扩散过程的重要性。

The shocked solar wind plasma, or magnetosheath, provides the basic input and outer boundary condition for the Earth's magnetosphere. The most direct access of this magnetosheath plasma into the magnetosphere and ionosphere occurs in the region of the outer polar cusp. Thus, an enhanced understanding of plasma processes at the magnetosheath/cusp interface is essential to the advancing magnetopause and boundary layer physics. Because of tailward bending of the magnetic field near the outer magnetospheric boundary, the entire magnetospheric boundary layer is mapped through this cusp region into the frontside, high- latitude ionosphere near local noon. Although the interaction of plasmas and fields in the outer cusp play a key role in linking the magnetosheath and boundary layer to the ionosphere, very few satellite measurements are available in this region. This project's objective is to advance the knowledge of plasma, field and plasma wave interactions in the outer and mid- altitude polar cusp with a focus on plasma and momentum transport, field fluctuations, and the resulting cusp current system. The investigators will identify and test those plasma and field interactions most relevant to enhancing unique observations available from satellite and used as a baseline sample of particle and field characteristics in the outer cusp and mid-altitude cusp regions. Although very limited, available observations in the outer cusp provide enough information on overall geometry and plasma conditions to apply state-of-the-art 2-D MHD and hybrid simulations of the magnetosheath-cusp interaction region including coupling to the ionosphere. Such simulations will provide information on the local time-dependent flows and magnetic fields in the outer cusp as well as the more nonlocal cusp/ionosphere current system. Understanding anomalous cross-field momentum transport is crucial for developing quantitative models of the cusp and dayside current systems. The PIs will therefore focus on shear-flow driven instabilities and associated turbulence and transport. Realistic 2-D and 3-D hybrid simulations of shear-flow across the magnetosheath/outer cusp and mid-altitude cusp wall boundaries will be completed. Theoretical predictions of electric and magnetic fluctuation spectra will be compared, especially with observed ULF-ELF wave spectra. In turn, cross-field transport will be calculated based on the observed fluctuation spectra to assess the importance of anomalous diffusion processes in the cusp region.