Energy transport and dissipation in the magnetosphere during geomagnetic storms

Major geomagnetic storms represent a significant dissipation of energy by the magnetosphere. The energy is derived from the solar wind Row and the subsequent powerful conversion of that energy takes several different forms. Ring current injection and decay, ionospheric Joule heating, particle precipitation into the atmosphere, and several related physical processes are exhibited clearly in large storm events. The modern-day constellation of operating spacecraft gives an unprecedented opportunity to study magnetic storm processes and energetics. This paper focuses on recent coronal mass ejection (CME) events that have been well-observed near the sun. These disturbances are followed from the sun to their arrival in near-Earth space. The reconfiguration of the magnetosphere under the driving influence of CME,: magnetic cloud events is examined and the energetics of various forms of input and output are assessed. It is concluded that the present observations in the ISTP era, along with modern modeling techniques, have given us new insights into geomagnetic stormtime energy dissipation. Ionospheric Joule heating and auroral particle precipitation account for a substantial majority of energy dissipation during CME-driven storms (i.e., greater than or similar to 70%). However, ring current energy injection due to moderate energy ions is also a key. Direct in situ observations of such ions are found to be crucially important because indices such as D-st may be contaminated by many other effects. (C) 2001 Elsevier Science Ltd. All rights reserved.