A new understanding of why the aurora has explosive characteristics

Abstract

ABSTRACT This article describes a new understanding of the explosive nature of auroras, called auroral substorms, on the basis of a series of processes, from power supply (dynamo), circuit/current, and dissipation (auroral substorms) – the electric current approach, in which the magnetosphere or more specifically the primary magnetosphere-ionosphere coupling system (the primary M-I system) plays a crucial role. The primary M-I system has an anomaly; it cannot dissipate the dynamo power much for about 1 h after the dynamo power becomes above 1011 w. This anomaly is due to a low conductivity of the quiet-time ionosphere to dissipate increasing power. Thus, the power is accumulated in the inner magnetosphere (at about 6 Re; Re = earth’s radius) as magnetic energy, inflating the inner magnetosphere. When the accumulated energy reaches to about 1016 J, the primary M-I system seems to become unstable and unload impulsively the accumulated magnetic energy, deflating the magnetosphere. This deflating process generates the secondly M-I system, which is associated with an electric field 5–50 mV/m and field-aligned currents, ionizing the ionosphere and increasing the conductivity. Therefore, the primary M-I system can perform like an ordinary electrical system. It is this particular nature that exhibits explosive auroral displays. This paper describes systematically and semiquantitatively key points of this series of processes based on a few decades of work. The electric current approach is rather ‘new’ in substorm research and thus is rudimental at its development stage, so that n crucial issues are mentioned for future studies at the end.