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

Abstract

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.