Magnetosphere-ionosphere coupling on meso- and macroscales

Much of the transfer of solar wind flow energy and momentum into the earth's magnetosphere occurs on the dayside magnetopause, where variations in the solar wind pressure and magnetic reconnection induce flows of plasma and magnetic flux within the magnetosphere. This thesis documents two aspects of these induced flows and their associated current systems based predominately on measurements from a large two-dimensional network of magnetometers situated below the dayside high-latitude ionosphere. First, the transient dayside phenomenon of traveling convection vortices (TCVs) is used to illustrate magnetosphere-ionosphere coupling on medium magnetospheric spatial scales. Within the ionosphere, the spatial structure and conjugate nature of TCV field-aligned currents is documented for the first time. Magnetospheric magnetohydrodynamic modeling is then used to show how transient magnetospheric flows near the sites of magnetopause deformation produce TCV field-aligned current systems with properties similar to those observed. Finally, the solar wind drivers that create the deformations of the magnetopause and cause TCVs are identified for the first time. On a much larger spatial scale, the timescale required to reconfigure the global magnetospheric and ionospheric flows in response to changes in the direction of the interplanetary magnetic field is determined. In the ionosphere, the initiation of flows in response to these changes occurs at all dayside local times within two minutes and the timescale for a complete reconfiguration of the flows is found to vary slightly as a function of local time, with the shortest time, five minutes, near local noon. Using magnetohydrodynamic models to investigate this timescale in the magnetosphere, it is found that the dayside magnetosphere reconfigures on similar timescales, with the flows reconfiguring just prior to those in the ionosphere. The consequence of these short timescales, which is illustrated in a statistical study, is that the coupled magnetosphere - ionosphere system is perpetually reconfiguring its flows in response to the variable solar wind on timescales as short as five to ten minutes. Thus, this thesis demonstrates that solar wind flow energy is transferred through the magnetopause, into the magnetosphere, and to ionosphere at two different spatial scales, on few-minute timescales.