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The photospheric boundary of Sun-to-Earth coupled models


The least understood component of the Sun-to-Earth coupled system is the solar atmosphere-the visible layers of the Sun that encompass the photosphere, chromosphere, transition region and low corona. Coronal mass ejections (CMEs), principal drivers of space weather, are magnetically driven phenomena that are thought to originate in the low solar corona. Their initiation mechanism, however, is still a topic of great debate. If we are to develop physics-based models with true predictive capability, we must progress beyond simulations of highly idealized magnetic configurations, and develop the techniques necessary to incorporate observations of the vector magnetic field at the solar photosphere into numerical models of the solar corona. As a first step toward this goal, we drive the SAIC coronal model with the complex magnetic fields and flows that result from a sub-photospheric MHD simulation of an emerging active region. In particular, we successfully emerge a twisted Omega-loop into a pre-existing coronal arcade. To date, it is not possible to directly measure the magnetic field in the solar corona. Instead, we must rely on nonpotential extrapolations to generate the twisted, pre-eruptive coronal topologies necessary to initiate data-driven MHD simulations of CMEs. We therefore investigate whether a non-constant-a force-free extrapolation can successfully reproduce the magnetic features of a self-consistent MHD simulation of flux emergence through a stratified model atmosphere. We generate force-free equilibria from simulated photospheric and chromospheric vector magnetograms, and compare these results to the MHD calculation. We then apply these techniques to an IVM (Mees Solar Observatory) vector magnetogram of NOAA active-region 8210, a source of a number of eruptive events on the Sun. (C) 2004 Elsevier Ltd. All rights reserved.

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