Massive plasma transport across the magnetospheric low-latitude boundary layer

本研究旨在阐明大质量等离子体在磁层低纬度边界层上的输运，这将构成一个与已知完全不同的等离子体片形成过程。低纬度的新输运过程在纯MHD模式中是不可能出现的，因此将涉及几十年来时间和空间尺度上的动力学耦合，从MHD到电子尺度。为了研究跨尺度耦合效应导致的输运过程，我们利用二维双流体模拟程序对MHD现象进行了数值模拟，其中包含有限电子惯性效应。具体来说，我们模拟了在速度剪切层中生长的MHD尺度涡的发展，并研究了MHD尺度涡内部与电子动力学的耦合是如何出现的。(1)当气流垂直于磁场时，涡旋卷起运动产生了一个强烈的电流层，其中由于有限的电子惯性而激发了不稳定性。这在涡旋外缘产生了次级速度剪切不稳定的播种扰动，产生了较小的涡旋，破坏了母涡旋。(2)当存在面内磁分量时，可以看到卷起运动拉伸的磁力线重新连接。相对于电子尺度，当涡旋尺寸较大时，观察到更多的动态重联。在任何一种情况下，在高度卷起的MHD尺度涡旋中观察到与电子尺度的耦合，这产生了在MHD框架内无法获得的新效应。预计这些影响将导致大量的运输通过速度剪切层。

This study aims at clarifying massive plasma transport across the magnetospheric low-latitude boundary layer, which would constitute a plasma sheet formation process that is totally different from the well-known. The new transport process at low-latitude is not expected in a pure MHD model and thus would involve coupling of dynamics over decades in temporal as well as spatial scales, from MHD down to the electron scales. In order to study the transport process that results from cross-scale coupling effects, we have performed numerical simulations of MHD phenomena using two-dimensional two-fluid simulation code including finite electron inertia effects.To be specific, we have simulated a development of MHD scale vortices that grow in velocity shear layers and have studied how the coupling to the electron dynamics emrges inside the MHD scale vortex.(1) When the flow is perpendicular to the magnetic field, the vortex roll-up motion produces an intese current layer, inside of which excited is an instability due to finite electron inertia. This produces a seeding perturbation for the secondary velocity shear instability at the outer edge of the vortex, which produces smaller vortices that destroy the parent vortex.(2) When there is an in-plane magnetic component, the field lines stretched by the roll-up motion are seen to reconnect. More dynamic reconnection is observed when the vortex size is larger relative to the electron scale.In either case, coupling to electron scales are observed within highly rolled-up MHD-scale vortices and this produces new effects not obtainable within the MHD framework. It is expected that these effects would lead to massive transport across the velocity shear layer.