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Ann. Geophys., 26, 955-1006, 2008
www.ann-geophys.net/26/955/2008/
© European Geosciences Union 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
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.
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