Electrical Charge Separation and Explosive Auroral Displays During the Substrom Expansion Phase

Abstract:

Magnetospheric substorms have often been referred to as auroral substorms. Understanding the formation of substorm auroras, their evolution, and the explosive nature of the auroral displays is the key to understanding the substorm process. The accumulation of the free magnetic energy in the magnetotail is only a necessary condition for the development of substorms. But the accumulated free magnetic energy is not the cause of the energy release; a mechanism to release this energy is required. The generation of parallel electrostatic fields associated with charge separation plays a crucial role in the acceleration of auroral charged particles. During this process, accumulated free magnetic energy can be explosively released and converted into substorm auroral particle energy.

We suggest that electrostatic fields are the most efficient and powerful means for auroral particle acceleration during substorms. We will elucidate the generation of parallel electrostatic fields by Alfvenic interaction in the inhomogeneous Solar Wind-Magnetosphere-Ionosphere (SW-M-I) coupling system. The generation of parallel electrostatic fields together with low density cavities represents a positive feedback process, resulting from Alfvenic interactions in the SW-M-I coupling system. The continuous large energy supply from Poynting flux during the expansion phase can support long-lasting strong parallel electrostatic fields and create explosive auroral displays.