Investigations of the Earth's magnetosphere with global magnetohydrodynamic simulations

We use LFM global MHD model to investigate and understand physical properties of Earth's magnetosphere and its coupling with ionosphere. We study three topics:; Earth's magnetosphere with steady northward IMF. We find short tail configuration (tail length ∼40 R_E) for steady state magnetosphere. Cusp reconnection, ionospheric four-cell pattern and concave 3D shape are clearly seen in simulations. Solar wind B_IMF and V_SW are varied. Ionospheric conductance is a minor effect in determining lobe size. Low dimensional models are derived for the B_IMF and V_SW dependences of tail size. One quiet-time northward IMF event with Geotail inside the tail is simulated. The simulated temporal evolution time and tail field magnitude agree well with observations. This affirms our model.; Magnetospheric substorms. We first simulate an ideal substorm which shows typical substorm behaviors with flow channels connecting the midtail and innertail region. The simulation captures typical features of a substorm. Then, we study the characteristic features of substorm dynamics using nonlinear dynamical techniques. Based on simulating large amount of substorm events, the analysis of the coupled vB_s-pseudo-AL index system derived from simulations shows first-order phase transition map, which is consistent with what obtained from real system by Sitnov et al., [2000] and is explained by the cusp catastrophe model. The coupled system also shows multiscale behavior in singular power spectrum. We find critical exponents relating input and output parameters of the magnetosphere and distinguishing second order phase transition model from SOC model.; Magnetosphere-ionosphere coupling. Models using outputs of the MHD model to simulate riometer and magnetometer observations are developed and applied to January 10, 1997 storm event. The results are compared with observations. Turbulent heating due to electrojet instabilities is important in calculating ionospheric absorption. A model describing the temporally and spatially averaged electron temperature is developed. The model agrees well with riometer observations. The magnetometer model uses computed ionospheric current density and energy-dependent height of the electrojet, to calculate perturbed magnetic field by implementing Biot-Savart law. The height-dependent model performs better than the fixed height model.