Detecting near-tail current sheet formation using isotropic boundaries: lessons from global MHD.

A number of recent studies suggests an existence of magnetotail current sheet configurations with tailward Bz gradient during the growth phase of the substorm. Such configurations are especially interesting since they are potentially unstable for different types of instabilities and can lead to explosive reconfiguration of the magnetosphere. However, the observations are rare and ability to observe tailward gradients is very limited. Here we use the global MHD configuration with near-tail Bz minimum to investigate the regions with adiabatic and non-adiabatic behavior of energetic particles. Thus we estimate the locations of the isotropic boundaries for the modelled POES-type spacecraft flybys. We expect that the lessons learned from global MHD simulation may become helpful in exploration of non-monotonic tail current sheet configuration using observations on low-orbiting spacecraft.

Particle Acceleration and Transport in the Magnetotail

<p>An outstanding problem of magnetospheric physics is to determine the energization of particles transported from the nightside to the dayside. To address this research problem, we leverage our simulation capabilities by combining three different simulation techniques: global magnetohydrodynamic (MHD) simulations, large-scale kinetic (LSK) particle tracing simulations, and large-scale particle in cell (PIC) simulations. First, we model a magnetotail reconnection event using an iPic3D simulation with initial and boundary conditions given by a global MHD simulation. The iPic3D simulation system includes the region of fast outflows emanating from the reconnection site that drives the formation of dipolarization fronts.Then, we follow millions of test particles that exit the iPic3D system using the electromagnetic fields from the MHD simulation as they convect to the dayside and quantify the different acceleration and transport mechanisms.</p>

Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

An auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes.