Table1_The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation.PDF

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales.

在地磁活跃时段，离子从磁尾被输运至内磁层，并被加速至数十至数百千电子伏（keV）的能量。这类成分混杂的高能离子中，以氢离子（H+）与氧离子（O+）为最主要的组分，成为内磁层等离子体压力的主导来源。离子输运与加速过程可发生于多种时空尺度，涵盖全球准稳态对流至局地脉冲注入事件，且其过程可能依赖于离子回旋半径。本研究旨在明确中尺度流结构与离子非绝热性对环电流形成的相对重要性。为此，我们采用了两类研究手段：一是借助磁流体动力学（MHD）模拟，在典型驱动条件下生成包含突发整体流（BBFs）的自洽电磁场；二是初始化与磁流体动力学模拟的等离子体矩参数匹配的注入试验粒子，随后依据动理学运动方程对其进行演化。研究表明，本模拟生成的突发整体流能够复现原位测量得到的热力学与磁学统计特征，且具备优异的数值鲁棒性。通过挖掘模拟数据，我们构建了包含十亿个数据点的数据集，将粒子输运过程与磁流体动力学流的特征建立关联。基于该数据集，我们证实中尺度泡——即局地熵亏缺区域——与粒子梯度漂移对离子输运至关重要。最后，通过使用质量各异的相同粒子系综开展分析，我们发现：氧离子（O+）的非绝热性会导致能量化过程与空间分布出现定性差异，而氢离子（H+）的非绝热性对粒子损失时标也存在不可忽视的影响。