A Global Wave-Driven Magnetohydrodynamic Solar Model With a Unified Treatment of Open and Closed Magnetic Field Topologies

Abstract

We describe, analyze and validate the recently developed Alfvén Wave Solar Model (AWSoM), a 3D global model starting from the top of the chromosphere and extending into interplanetary space (up to 1-2 AU). This model solves the extended twotemperature magnetohydrodynamics equations coupled to a wave kinetic equation for low frequency Alfvén waves. In this picture, heating and acceleration of the plasma are due to wave dissipation and wave pressure gradients, respectively. The dissipation process is described by a fully developed turbulent cascade of counter-propagating waves. We adopt a unified approach for calculating the wave dissipation in both open and closed magnetic field lines, allowing for a self-consistent treatment of any magnetic topology. Wave dissipation is the only heating mechanism assumed in the model, and no geometric heating functions are invoked. Electron heat conduction and radiative cooling are also included. We demonstrate that the large-scale, steady-state (in the co-rotating frame) properties of the solar environment are reproduced, using three adjustable parameters: the Poynting flux of chromospheric Alfvén waves, the perpendicular correlation length of the turbulence, and a pseudo-reflection coefficient. We compare model results for Carrington Rotation 2063 (November-December 2007) to remote observations in the EUV and X-ray ranges from STEREO, SOHO and Hinode spacecraft, as well as to in-situ measurements performed by Ulysses. The model results are in good agreement with observations. This is the first global model capable of simultaneously reproducing the multi-wavelength observations of the lower corona and the wind structure beyond Earth's orbit.

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

“…We find that the model by Hansteen & Leer (1995) severely underpredicts the electron density and this causes both in-situ charge states and line intensities to be exceedingly low. The 1D model by Cranmer et al (2007) and the 3D model by Oran et al (2013) provide qualitatively similar results: they are able to reproduce line intensities of ions formed at subcoronal temperatures but underpredict the intensities of coronal lines and the plasma frozen-in charge state distribution. The discrepancies are due to the Delay Effect, namely, the difficulty at ionizing that the accelerating fast wind experiences as it travels from its source region in the chromosphere into the corona and interplanetary space.…”

“…In order to provide a more consistent comparison with the Hansteen and Cranmer models, which are developed without any observational inputs for the magnetic field strength and geometry corresponding to the particular observations of the solar spectra we use, we chose to use the results obtained with a dipole magnetic field boundary and the Oran et al (2013) version of the model. Landi et al (2012d) found that for almost all elements, the charge state distribution significantly deviates from equilibrium almost everywhere along the wind trajectory by factors up to 10 for some ions.…”

“…The plasma electron temperature, density, and velocity of the wind starting point are listed in Table 1. It is important to note that the boundary temperature in the Michigan model is set at a larger temperature than in the other two models because this model does not extend below that temperature (see Oran et al 2013 for details).…”

Alfvén Wave Turbulence as a Coronal Heating Mechanism: Simultaneously Predicting the Heating Rate and the Wave-induced Emission Line Broadening

“…Separate pressure equations for electrons and protons allow the inclusion of non-ideal MHD processes such as electron heat conduction, radiative cooling and electron-proton heat exchange. For the sake of brevity we will not repeat the full set of governing equations here and refer the reader to Sokolov et al (2013) and Oran et al (2013). It is worthwhile, however, to briefly discuss the wave dissipation mechanism, since it is the only heating mechanism assumed in the model and it controls the magnitude of the Alfvénic perturbations considered in this work.…”

“…In this work we use the recently developed Alfvén Wave Solar Model (AWSoM) Oran et al 2013), a global model of the solar atmosphere driven by Alfvén wave energy, which is propagated and dissipated in both open and closed magnetic field lines. The model extends from the top of the chromosphere and up to 1-2AU.…”