Inner magnetospheric plasma interactions and coupling with the ionosphere Mei-Ching Fok, Yusuke Ebihara, and Thomas E. Moore The inner magnetosphere occupies a vast volume in space containing a relatively low-density mixture of hot and cold plasmas: the ring current, plasmasphere and radiation belt. Energy is transferred from the ring current to the cold plasmas through Coulomb collisions and wave-particle interactions, producing temperature enhancements in the plasmasphere. The plasma waves generated in the plasmasphere cause pitch-angle and energy diffusion of the energetic particles. The magnetic disturbances generated from the ring current alter the drift paths of radiation belt particles, causing radiation belt flux dropout during magnetic storm main phases. The ionosphere is filled with dense and cold plasmas in a 1000-km-thick shell above the EarthÕs surface at 100 km altitude. Despite the distinct differences in size, location and physical properties, the ionosphere and the inner magnetosphere are tightly connected to each other. The ionosphere is an important source of magnetospheric ions. Energy transported down from the inner magnetosphere to the ionosphere produces observable temperature enhancements and optical emissions in the ionosphere. The electric coupling between the ionosphere and magnetosphere explains features such as shielding field, non-linear response of the ring current to the plasmasheet source, and the post-midnight enhancement of the storm-time ring current flux. Even though many signatures are well described from the perspective of magnetosphere-ionosphere coupling, there are still unanswered questions, for example, the precise roles of wave-particle interactions in ring current loss and plasmaspheric heating, the cause of rapid storm initial recovery, the source of O enhancement at substorm expansion, and the causes of outer radiation belt enhancement during storm recovery. The unresolved questions can be answered through careful cross analysis of the observational data from the ongoing and future imaging and multi-point missions with simulation results of large-scale modeling. _______________ Advances in Polar Upper Atmosphere Research, 19, 106-134, 2005