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

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.