Pressure-Driven Currents Derived from Global ENA Images by IMAGE/HENA

E.C. Roelof (JHU/APL, Laurel, MD 20723)

The global ion distributions extracted from ENA images obtained by IMAGE/HENA
can be used to calculate the distribution of plasma pressure throughout the
ring current region.  Knowing the plasma pressure and the magnetic field, one
can calculate the three-dimensional current system that is driven by the
pressure gradient, assuming force equilibrium with divJ=0. For an isotropic
pressure tensor P=PI, the complete current intensity J can be calculated from
Euler potentials, one of which is the pressure (P) itself, and the other (Q)
is the partial volume of the magnetic flux tube measured from the minimum-B
equator.  For a dipole field, the latter is a simple analytic function, but
in principle Q can be calculated from any magnetic field model. If P is not
isotropic, a solution still exists, but it is not directly in Euler
potentials. Examples derived from the HENA images will be presented of the
topology of the global pressure-driven current system and the field-aligned
(Region 2) currents that are driven into the ionosphere.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions,
3 - 6 February 2004, Yosemite, California, USA