MHD Ballooning Instability in the Plasma Sheet

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Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial ... continued below

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Cheng, C.Z. & Zaharia, S. October 20, 2003.

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Description

Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

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1 MB pages

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INIS; OSTI as DE00820113

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  • Other Information: PBD: 20 Oct 2003

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  • Report No.: PPPL-3890
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/820113 | External Link
  • Office of Scientific & Technical Information Report Number: 820113
  • Archival Resource Key: ark:/67531/metadc740883

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • October 20, 2003

Added to The UNT Digital Library

  • Oct. 18, 2015, 6:40 p.m.

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  • April 18, 2016, 1:01 p.m.

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Cheng, C.Z. & Zaharia, S. MHD Ballooning Instability in the Plasma Sheet, report, October 20, 2003; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc740883/: accessed December 14, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.