Articles | Volume 26, issue 4
Ann. Geophys., 26, 955–1006, 2008
Ann. Geophys., 26, 955–1006, 2008
13 May 2008
13 May 2008

Transient and localized processes in the magnetotail: a review

A. S. Sharma1, R. Nakamura2, A. Runov2,*, E. E. Grigorenko3, H. Hasegawa4, M. Hoshino5, P. Louarn6, C. J. Owen7, A. Petrukovich3, J.-A. Sauvaud6, V. S. Semenov8, V. A. Sergeev8, J. A. Slavin9, B. U. Ö. Sonnerup10, L. M. Zelenyi3, G. Fruit6, S. Haaland11, H. Malova3, and K. Snekvik11 A. S. Sharma et al.
  • 1Department of Astronomy, University of Maryland, College Park, USA
  • 2Space Research Institute, Austrian Academy of Sciences, Graz, Austria
  • 3Space Research Institute, Russian Academy of Sciences, Moscow, Russia
  • 4Institute of Space and Astronautical Science, Kanagawa, Japan
  • 5University of Tokyo, Tokyo, Japan
  • 6CESR/CNRS, Toulouse, France
  • 7Mullard Space Science Laboratory, University College, London, UK
  • 8Institute of Physics, St. Petersburg State University, St. Petersburg, Russia
  • 9Laboratory for Extraterrestrial Physics, NASA GSFC, Greenbelt, USA
  • 10Thayer School of Engineering, Dartmouth College, Hanover, USA
  • 11University of Bergen, Bergen, Norway
  • *currently at: Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA, USA

Abstract. Many phenomena in the Earth's magnetotail have characteristic temporal scales of several minutes and spatial scales of a few Earth radii (RE). Examples of such transient and localized mesoscale phenomena are bursty bulk flows, beamlets, energy dispersed ion beams, flux ropes, traveling compression regions, night-side flux transfer events, and rapid flappings of the current sheet. Although most of these observations are linked to specific interpretations or theoretical models they are inter-related and can be the different aspects of a physical process or origin. Recognizing the inter-connected nature of the different transient and localized phenomena in the magnetotail, this paper reviews their observations by highlighting their important characteristics, with emphasis on the new results from Cluster multipoint observations. The multi-point Cluster measurements have provided, for the first time, the ability to distinguish between temporal and spatial variations, and to resolve spatial structures. Some examples of the new results are: flux ropes with widths of 0.3 RE, transient field aligned currents associated with bursty bulk flows and connected to the Hall current at the magnetic reconnection, flappings of the magnetotail current sheet with time scales of 100 s–10 min and thickness of few thousand km, and particle energization including velocity and time dispersed ion structures with the latter having durations of 1–3 min. The current theories of these transient and localized processes are based largely on magnetic reconnection, although the important role of the interchange and other plasma modes are now well recognized. On the kinetic scale, the energization of particles takes place near the magnetic X-point by non-adiabatic processes and wave-particle interactions. The theory, modeling and simulations of the plasma and field signatures are reviewed and the links among the different observational concepts and the theoretical frameworks are discussed. The mesoscale processes in the magnetotail and the strong coupling among them are crucial in developing a comprehensive understanding of the multiscale phenomena of the magnetosphere.