Simulation study of near-Earth space disturbances: 2. Auroral substorms

A substorm is a transient phenomenon that lasts for only 1-2h. One significant manifestation of the substorm is a sudden brightening of the aurora on the nightside. Simultaneously, the auroral electrojets are abruptly intensified in the ionosphere, disturbing the geomagnetic field in the polar region. The near-Earth space environment is highly disturbed, which manifests as an earthward fast flow of plasma, a sudden change in the magnetic field, or a sudden increase in hot plasma. Such disturbances are known to severely affect human society. The ultimate cause of the disturbances is the solar wind, but an explanation of the chain of processes leading from solar wind to the ionosphere is problematic. Here, the evolution of the auroral substorm is reviewed based on the results of a global magnetohydrodynamics (MHD) simulation, called a REProduce Plasma Universe (REPPU) code. The REPPU code is shown to reproduce many aspects of the auroral substorms and to be useful for understanding the primary chain processes from the solar wind to the ionosphere.