Space- and ground-based investigations of magnetosphere-ionosphere coupling

It is increasingly recognized that study of the magnetosphere or ionosphere in isolation cannot reveal the complex influence of each on the other. Rather, both should be considered as components of a coupled system, which requires that multi-point, multi-instrument measurements be made from the ground and in space simultaneously. In addition, ground-based observations provide a global context within which to interpret point measurements in space, and space-based measurements give detailed physical insights into the magnetospheric processes which manifest themselves in the ionosphere. Ionospheric observations can include coherent radar measurements of ionospheric convection flow, incoherent radar measurements of ionospheric density and temperature, magnetometer measurements of ionospheric currents, and optical measurements of auroral luminosity. We will discuss recent advances made in the understanding of the coupled ionosphere-magnetosphere system, both dayside and nightside, when such observations are combined with space-based measurements, esp. the Cluster mission. Future opportunities afforded by the combination of Cluster with the new Double Star mission will also be explored.