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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 5
Nonlin. Processes Geophys., 17, 467–479, 2010
https://doi.org/10.5194/npg-17-467-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Nonlinear plasma waves in space and laboratories

Nonlin. Processes Geophys., 17, 467–479, 2010
https://doi.org/10.5194/npg-17-467-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Review article 27 Sep 2010

Review article | 27 Sep 2010

Magnetic Decreases (MDs) and mirror modes: two different plasma β changing mechanisms

B. T. Tsurutani1,2, G. S. Lakhina3, O. P. Verkhoglyadova1,4, E. Echer5, and F. L. Guarnieri6 B. T. Tsurutani et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 2Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany
  • 3Indian Institute of Geomagnetism, Navi Mumbai, India
  • 4CSPAR, University of Alabama, Huntsville AL, USA
  • 5Instituto Nacional Pesquisas Espaciais, São Jose dos Campos, SP, Brazil
  • 6Universidade do Vale do Paraíba, São Jose dos Campos, SP, Brazil

Abstract. We discuss two different physical processes that create localized high β plasma regions. One is nonlinear wave-steepening, generating magnetic decreases (MDs) by a ponderomotive force. The other is the mirror instability generating alternating high and low β plasma regions. It is demonstrated that MDs and mirror modes are observationally quite different structures. MDs spatially occur in interplanetary space and mirror modes primarily in planetary magnetosheaths. MDs are characterized by: 1) variable (exponentially decreasing number with increasing) angular changes, 2) variable (exponentially decreasing) thicknesses, and 3) no characteristic inter-event spacings. In sharp contrast, mirror modes are characterized by: 1) little or no angular changes across the structures, 2) a characteristic scale size, and 3) are quasiperiodic in nature.

Arguments are presented for the recently observed magnetic dips in the heliosheath being mirror mode structures. The sources of free energy for instability are discussed. Both structures are important for energetic particle transport in astrophysical and heliospheric plasmas.

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