We perform the first ever global-scale, altitude-dependent analysis of polar ionospheric conductivity variability using spectrally resolved in situ satellite particle measurements. With an empirical orthogonal function analysis we identify three primary modes of three-dimensional variability related to ionospheric footprints of the quiet and disturbed geospace environment: (1) perturbation of the quasi-permanent auroral oval, (2) differing projections of electron precipitation during southward and northward interplanetary magnetic field, and (3) a likely imprint of variation in Alfvenic Poynting flux deposition. Together, these modes account for >50% of the total conductivity variability throughout the E region ionosphere. Our results show that height-integrated conductance and height-dependent conductivities are distinctly different, underscoring the importance of studying the ionosphere in three dimensions. We provide the framework for future three-dimensional global analysis of ionosphere-magnetosphere coupling.
