MHD Model Iridium Birkeland Currents Comparison Birkeland currents

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

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

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 1/8 th of the total for northward IMF: Poynting flux = 45 GW, 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 10 x too low and in the wrong place (by 6 hours) unless a realistic magnetic field is used [Brandt et al. , 2004].

• Particle and Poynting flux – not coincident • Precipitation power: 6 GW • Poynting flux: 45 GW ~ 7. 5 x particle 16 July 2000: 1700 -1800 UT Iridum/DMSP IMAGE/FUV -DMSP