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MHD Model – Iridium Birkeland Currents Comparison

This study examines Birkeland currents derived from Iridium observations, revealing significant global distribution and relationships with field-aligned currents in MHD models. Our analysis highlights essential areas for model improvement and addresses the absence of equatorward currents and nightside currents, linking these discrepancies to missing physics and numerical diffusion. Results emphasize the need for realistic magnetic field configurations to align model outputs with direct observations, informing future advancements in modeling techniques, particularly regarding ionospheric conductivity and precipitation.

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MHD Model – Iridium Birkeland Currents Comparison

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  1. MHD Model – Iridium Birkeland Currents Comparison • Birkeland currents from Iridium are globally distributed: map to entire simulation volume • Field aligned current is a direct MHD variable that is conserved across the high-to-low altitude mapping • Comparison reveals specific ways that models need to be improved • Results direct future modeling development

  2. Iridium LFM-MHD Model Comparison • Equatorward currents are missing in model: missing physics • Difference between low and high resolution: numerical diffusion • Nightside currents missing: errors in modeled ionospheric conductivity

  3. IMAGE-Iridium Inter-comparison • Establish correlation of indirect remote sensing results with direct but global-scale in-situ observations • Aurora indicate physical processes but the correspondence is not direct: → Occurrence of high latitude dayside aurora is governed by the Knight relation [Korth et al., 2004]. → A northward IMF case: particle energy input is only 1/8th of the total for northward IMF: Poynting flux = 45GW, particles 6 GW & aurora do not show where the Poynting flux is. • Ion pressure is almost certainly the source of Region 2. How well we understand the ring current and inner magnetosphere is well tested by comparing IMAGE/HENA Region 2 currents against Iridium results: → IMAGE/HENA currents are 10x too low and in the wrong place (by 6 hours) unless a realistic magnetic field is used [Brandt et al., 2004].

  4. Particle and Poynting flux – not coincident • Precipitation power: 6 GW • Poynting flux: 45 GW ~ 7.5x particle 16 July 2000: 1700-1800 UT Iridum/DMSP IMAGE/FUV -DMSP

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