Magnetosphere-Ionosphere Coupling as Observed in Total Electron Content Data

Electrodynamic coupling between the magnetosphere and ionosphere (M-I) has a direct influence on ionospheric structure and dynamics. Indirect forcing is possible acting through changes in the composition and dynamics of the underlying neutral atmosphere (thermosphere). Although energy inputs generally occur at high latitude, the impacts are global in scope because of high ionospheric conductances. Thermospheric circulation changes propagate equatorward and affect the middle to low latitude ionosphere within a few hours. We discuss how total electron content (TEC) data available on global scales is used to investigate M-I coupling and its consequences. Subauroral electric fields (also known as SAPS) create high-speed plasma flows at middle latitudes during geomagnetic disturbances. Dayside dawn-to-dusk electric fields create global scale ionospheric perturbations affecting the full range of low to middle latitudes over time scales as short as 1-2 hours. The global TEC data set is a unique resource for investigating the combined impacts of localized high speed and global plasma flows. TEC data have also been used to characterize inner magnetospheric structures such as the plasmapause, including plumes, and how these boundaries vary during storms and substorms. TEC combined with other datasets such as optical imagers and convection radar is an important tool for increasing scientific understanding of M-I coupling. A significant recent event is the launch of the Radiation Belt Storm Probes mission designed to answer fundamental questions on the energization and fluxes of radiation belt particles during quiet and disturbed periods. We will discuss how TEC combined with spacecraft data is an emerging resource for these investigations.