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Ann. Geophys., 22, 251-265, 2004
www.ann-geophys.net/22/251/2004/
© European Geosciences Union 2004
3-D force-balanced magnetospheric configurations
S. Zaharia1,3, C. Z. Cheng1, and K. Maezawa2
1Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, NJ 08543, USA
2Institute of Space and Astronautical Science, Yoshinodai 3-1-1, Sagamihara, Kanagawa, 229 8510, Japan
3Now at Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
Abstract. The knowledge of plasma pressure is essential for many physics
applications in the magnetosphere, such as computing magnetospheric
currents and deriving mag-netosphere-ionosphere coupling. A thorough
knowledge of the 3-D pressure distribution has, however, eluded the
community, as most in situ pressure observations are either in the
ionosphere or the equatorial region of the magnetosphere. With the
assumption of pressure isotropy there have been attempts to obtain the
pressure at different locations,by either (a) mapping observed data
(e.g. in the ionosphere) along the field lines of an empirical
magnetospheric field model, or (b) computing a pressure profile in the
equatorial plane (in 2-D) or along the Sun-Earth axis (in 1-D) that is
in force balance with the magnetic stresses of an empirical
model. However, the pressure distributions obtained through these
methods are not in force balance with the empirical magnetic field at
all locations. In order to find a global 3-D plasma pressure
distribution in force balance with the magnetospheric magnetic field,
we have developed the MAG-3-D code that solves the 3-D force balance
equation  computationally. Our
calculation is performed in a flux coordinate system in which the
magnetic field is expressed in terms of Euler potentials as
 . The pressure distribution,
 , is prescribed in the equatorial plane and is based
on satellite measurements. In addition, computational boundary
conditions for ψ surfaces are imposed using empirical field
models. Our results provide 3-D distributions of magnetic field,
plasma pressure, as well as parallel and transverse currents for both
quiet-time and disturbed magnetospheric conditions.
Key words. Magnetospheric physics (magnetospheric configuration
and dynamics; magnetotail; plasma sheet)
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