Dayside proton aurora: Comparisons between global MHD simulations and IMAGE 
observations

J. Berchem, S.A. Fuselier, S. Petrinec, H.U. Frey, and J.L. Burch


The IMAGE mission provides a unique opportunity to evaluate the accuracy of
current global models of the solar wind interaction with the EarthÕs
magnetosphere. In particular, images of proton auroras from the Far Ultraviolet
Instrument (FUV) onboard the IMAGE spacecraft are well suited to support
investigations of the response of the EarthÕs magnetosphere to interplanetary
disturbances. Accordingly, we have modeled two events that occurred on June 8
and July 28, 2000, using plasma and magnetic field parameters measured upstream
of the bow shock as input to threedimensional magnetohydrodynamic (MHD)
simulations. This paper begins with a discussion of images of proton auroras
from the FUV SI-12 instrument in comparison with the simulation results. The
comparison showed 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. Subsequently, the IMAGE
observations are analyzed in the context of the dayside magnetosphereÕs
topological changes in magnetic field and plasma flows inferred from the
simulation results. Finding include 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 in
direction and the solar wind dynamic pressure varies. The global simulations
also indicate that some of the transient patterns observed by IMAGE are
consistent with sporadic reconnection processes. Global merging patterns found
in the simulations agree with the antiparallel merging model, though locally
component merging might broaden the merging region, especially in the region
where shocked solar wind discontinuities first reach the magnetopause. Finally,
the simulations predict the accretion of plasma near the bow shock in the
regions threaded by newly open field lines on which plasma flows into the
dayside ionosphere are enhanced. Overall the results of these initial
comparisons between global MHD simulation results and IMAGE observations
emphasize the interplay between reconnection and dynamic pressure processes at
the dayside magnetopause, as well as the intricate connection between the bow
shock and the auroral region. 

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Space Science Reviews, 109 (1-4), 313-349, 2003.