Global MHD Simulation of Dayside Proton Aurora: Comparisons with IMAGE Observations

The IMAGE mission provides a unique opportunity to test the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. We report the results of comparisons between the output of three-dimensional magnetohydrodynamic (MHD) simulations and images from the Far Ultraviolet Instrument (FUV) SI-12 instrument on board IMAGE showing the occurrence of proton auroras during several periods of relatively high solar wind dynamic pressure. We find a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Examining the IMAGE observations in the context of the dayside magnetosphere's topological changes inferred from the simulations, we find that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the IMF changes direction and the solar wind dynamic pressure varies. However, the global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with some additional sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model, though component merging might locally broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause.