The magnetosphere–ionosphere system from the perspective of plasma circulation: A tutorial

This tutorial review examines the role of O in the dynamics of magnetosphere–ionosphere coupling. The life cycle of an O plasma element is considered as it circulates from the midto high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvénic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current ‘‘pressure cookers.’’ Observational evidence indicating that O dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O-enriched plasma on solar wind–magnetosphere–ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging. r 2006 Elsevier Ltd. All rights reserved.