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    Equilibrium structure and dynamics of near-earth plasma sheet during magnetospheric substorms

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    Zhang_L_1997.pdf
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    Author
    Zhang, Lin
    Chair
    Otto, Antonius
    Committee
    Sentman, Davis
    Smith, Roger
    Watkins, Brenton
    Keyword
    Plasma physics
    Geophysics
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/9509
    Abstract
    A magnetofrictional method and MHD simulation are used to study MHD equilibria and dynamic evolution of the Earth's magnetosphere during a substorm growth phase. I suggest that the new "entropy anti-diffusion instability" associated with plasma transport across field lines leads to an enhanced entropy gradient and accelerates the formation of a thin current sheet during the final substorm growth phase. Based upon the MHD simulations with a pressure diffusion term, I confirm that entropy anti-diffusion instability can lead to a very thin current sheet with $B\sb{z} < 0.5nT$ and thickness $<$1000km in the near-earth magnetotail ($x \sim -8$ to $-20R\sb{e}$) during the growth phase of substorm. The formation of the thin current sheet can explain the observed explosive growth phase of substorms. In the study of magnetotail equilibrium configurations, it is found that the profile of the magnetic field strength B$\sb{z}$ component in the equatorial plane is mainly determined by the entropy $S(A)\ (S = pV\sp\gamma)$ on magnetic flux tubes. I obtain self-consistent equilibria of the Earth's magnetosphere with very strong lobe fields and a monotonically increasing $B\sb{z}$ component towards the Earth. It is also confirmed that an enhancement of the lobe flux favors the formation of a current sheet during the early substorm growth phase. However, my results do not support the notion that a critical amount of the lobe flux is required for a collapse of the tail current sheet.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 1997
    Date
    1997
    Type
    Dissertation
    Collections
    Physics

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