Global Proton Pressure Distributions in the Inner Magnetosphere Derived by
IMAGE/HENA Using Realistic Magnetic Fields and Their Relation to Birkeland
Currents Measured by Iridium

B.J. Anderson, P.C. Brandt, R. DeMajistre, E.C. Roelof, D.G. Mitchell, H. Korth,
and N.A. Tsyganenko


Comparisons between IMAGE/HENA derived proton pressure-driven Birkeland currents
and Iridium observations at ionospheric altitudes have shown that the IMAGE/HENA
inversions currents are sensitive to the magnetic field used in the HENA
inversion. This motivated improving the HENA inversion technique by using the
latest Tsyganenko magnetic field model which was upgraded to represent
storm-time effects in the inner magnetosphere. We present results using this new
inversion. Since the retrieved proton fluxes are in the 10-200 keV range, we can
only calculate the partial plasma pressure, about 60 percent of the total
pressure, in the inner magnetosphere. We then calculate the electrical currents
associated with that pressure distribution via the force balance equation (using
the same Tsyganenko field model). The HENA proton pressures are compared against
in-situ satellite observations as a cross check on the inversion. The more
stringent test of the inversion is provided by comparing the Birkeland currents
calculated from the HENA data against those derived from the magnetometer data
obtained from the Iridium satellites. This inter-comparison not only allows us
to validate the HENA inversions but also to shed light on the contribution of
the proton pressure to the total current system and how this contribution
depends on solar wind and magnetospheric conditions.

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Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004