Substorm Current Wedge Revisited

Almost 40 years ago the concept of the substorm current wedge was developed to explain the magnetic signatures observed on the ground and in geosynchronous orbit during substorm expansion. In the ensuing decades new observations, including radar and lowaltitude spacecraft, MHD simulations, and theoretical considerations have tremendously advanced our understanding of this system. The AMPTE/IRM, THEMIS and Cluster missions have added considerable observational knowledge, especially on the important role of fast flows in producing the stresses that generate the substorm current wedge. Recent detailed, multi-spacecraft, multi-instrument observations both in the magnetosphere and in the ionosphere have brought a wealth of new information about the details of the temporal evolution and structure of the current system. While the large-scale picture remains valid, the new L. Kepko (B) NASA Goddard Space Flight Center, Greenbelt, MD, USA e-mail: [email protected] R.L. McPherron University of California, Los Angeles, Los Angeles, CA, USA O. Amm Finnish Meteorological Institute, Helsinki, Finland S. Apatenkov · V. Sergeev St. Petersburg State University, St. Petersburg, Russia W. Baumjohann · R. Nakamura Space Research Institute, Austrian Academy of Sciences, Graz, Austria J. Birn Space Science Institute, Boulder, CO, USA M. Lester University of Leicester, Leicester, UK T.I. Pulkkinen Aalto University School of Electrical Engineering, Aalto, Finland