Combined Particle and Fluid Simulations of the Magnetosphere, Its Boundary Layers and Current Systems

9321665 Winglee MHD是用于模拟磁层动力学的主要工具之一。我们从解析和数值两方面证明了MHD所基于的阻性欧姆定律不适用于磁层，因为许多等离子体和能量传输发生在薄的边界层上，因此给出了对磁层电流系统的不完全描述。我们首次能够确定控制(1)磁层边界层结构的本征粒子效应，(2)重新连接所需的电流片中的耗散，以及(3)进出日侧和黑夜极光区域的电流。这些影响是通过粒子/两种流体模拟确定的，这些模拟通过消除由于施加异常电阻率而引起的模糊性和通过解决区域1和2极光电流的映射来提供相对于单一流体MHD的进步。拟议的工作旨在发展(I)2-D和3-D区域粒子模拟，以确定磁层顶、LLBL和磁尾内粒子分布的结构、电流系统和性质，(Ii)修改3-D双流体模拟，以提供从这些区域发出的进入极光区域的电流及其通过它们在磁层顶和磁尾电流片上产生的耗散而对全球动力学的影响的全面全球地图，以及(Iii)粒子和流体模拟与Tsyganenko模型之间的交叉校准，以测试建模的准确性，更重要的是，以帮助建立一个模型，预测磁层和极光电流的平均响应。3-D全球模拟将基于一组经过修改的双流体方程，这些方程已经针对粒子模拟进行了测试校准。它使用了广义欧姆定律的修改版本，并加入了一个额外的方程，描述了导致日侧和黑夜极光电流的电子运动。粒子模拟将结合用于场解的新的有限差分算法，该算法可以实现可变网格间距，从而使得能够对动力学过程进行大规模的区域模拟。拟议的工作将通过提供进出磁层的磁力线和电流的全球地图，并通过确定与关键边界层有关的结构和粒子分布，对磁层物理学有重要的应用。它有可能在地面观测磁场扰动和极光椭圆运动与航天器现场观测磁场扰动和极光椭圆运动与航天器现场观测高能粒子之间建立直接联系。此外，通过与Tsyganenko模型的比较，我们将能够建立一个平均磁层模型，该模型可以用来预测在普遍的太阳风条件下由Kp确定的磁层活动。所有这些应用都符合美国国家科学基金会磁层计划的重要目标。***

9321665 Winglee MHD is one of the main tools used to model the dynamics of the magnetosphere. We show both analytically and numerically that the resistive Ohm's law on which MHD is based is not appropriate for the magnetosphere because much of the plasma and energy transport occurs across thin boundary layers and as a result gives an incomplete description of the magnetospheric current system. We are able to identify for the first time the intrinsic particle effects that control (i) the structure of magnetospheric boundary layers, (ii) the dissipation in current sheets needed for reconnection and (iii) the currents that map into and out of the dayside and nightside auroral regions. These effects are determined from particle/two fluid simulations that provide an advancement over single fluid MHD by removing ambiguities arising from the imposition of anomalous resistivity and by resolving the mapping of the region 1 nd 2 auroral currents. The proposed work seeks development of (i) regional particle simulations in both 2-D and 3-D to identify the structure, current system, and properties of the particle distributions within the magnetopause, LLBL and magnetotail, (ii) modified two-fluid simulations in 3-D to provide full global mapping of the currents emanating from these regions into the auroral region and their effect on the global dynamics through the dissipation they produce on the magnetopause and magnetotail current sheets, and (iii) cross-calibration between the particle and fluid simulations with the Tsyganenko model to test the accuracy of the modeling and, more importantly, to aid in the construction of a model that predicts the average response of the magnetosphere and the auroral currents. The 3-D global simulations are to be based on a modified set of two-fluid equations that have been test calibrated against particle simulations. It uses a modified version of the generalized Ohm's law and incorporates an additional equation describing the electron motion responsible for the dayside and nightside auroral currents. The particle simulations will incorporate a new finite-difference algorithm for the field solutions that can enable variable grid spacing and thereby enable large scale regional modelling of kinetic processes. The proposed work will have important applications to magnetospheric physics by providing global mapping of both magnetic field lines and currents into and out of the magnetosphere, and by identifying the structure and particle distributions associated with critical boundary layers. It has the potential of providing a direct link between ground-based observations of magnetic field perturbations and the motion of the auroral oval with in-situ spacecraft observations of magnetic field perturbations and the motion of the auroral oval with in-situ spacecraft observations of energetic particles. In addition, through the comparison with the Tsyganenko model we will be able to construct an average magnetospheric model that can be used to predict the magnetospheric activity as determined by Kp for prevailing solar wind conditions. All these applications meet important objectives of NSF's Magnetospheric Program. ***