(For description of the older model version(s) used in runs completed prior to 2013 see: http://ccmc.gsfc.nasa.gov/models/swmf_desc_old.php ).
The Alfven-Wave driven SOlar wind Model (AWSOM) is part of the Space Weather Modeling Framework (SWMF). The SWMF has been developed by the Center for Space Environment Modeling (CSEM) team led by Tamas Gombosi at the University of Michigan (Toth et al. 2012). AWSOM uses the solar corona (SC) and inner heliosphere (IH) components of the SWMF. Both the SC and IH models are based on the BATS-R-US MHD code, which is a 3-dimensional block-adaptive code.
The AWSOM model can produce a solution of the ambient corona for a Carrington Rotation selected by the user. The computational domain starts from the top of the chromosphere, and includes the transition region, corona, and the inner heliosphere. This model solves the magnetohydrodynamic (MHD) equations with separate ion and electron temperatures and two equations for the Alfven wave turbulent energy densities propagating along and counter the magnetic field lines. The Alfvenic Poynting flux is assumed to be emanating from the chromosphere. The interaction of the wave field with the MHD plasma serves to both accelerate and heat the plasma. This model includes Spitzer electron heat conduction and radiative cooling (calculated using a CHIANTI table) in the lower corona. Coronal heating is achieved through observationally motivated turbulent Alfven wave dissipation. This mechanism uses a dissipation length, Lperp, which depends on the magnetic field magnitude. It is assumed that some of the wave energy propagating away from the Sun is reflected backwards due to inhomogeneities. The detailed reflection process is now directly simulated. Before 2014, Jan 30, a reflection coefficient, Cref, was used as an input parameter (see restrictions below). Heating due to the interaction of outward propagating and reflected waves is dominant in the coronal holes. In closed magnetic field line regions, counter propagating wave dissipation is dominant. By the date of the document, the most complete description of the model is provided in Sokolov et al (2013). The detailed description of the wave reflection is provided in Van Der Holst et al (2014).
The inner boundary conditions for the magnetic field are taken from a synoptic magnetogram (GONG/MDI). The temperature and density at the top of the chromosphere are set to be uniform at 50,000 [K] and 2x1011 [cm-3], respectively. The radial velocity is set to zero. The outer boundary conditions are superfast outflow.
The initial conditions for the solar wind plasma are based on a Parker solution. The initial magnetic field is based on the Potential Field Source Surface Model obtained from the synoptic magnetogram with the Finite Difference Iterative Potential Solver (FDIPS, Toth et al. 2011).
The coronal code iterates for (4000) steps until the solution has settled into a steady state. (The number of steps may change as we study the number of iterations that the solar coronal component needs to converge). Some cases may not reach equilibrium - the user should check the convergence plots provided with the output to confirm convergence to an equilibrium, and provide feedback to model developers. Then the heliospheric component evolves a solution consistent with the coronal model for 4,000 iterations.
The coronal component uses a non-uniform spherical grid extending from the chrompshere to 24 solar radii in the radial direction. The grid is stretched in the radial direction so that the transition region is resolved, with a minimal cell size of 0.001 solar radii in the radial direction. The total number of grid cells is ~2-3 million. The heliospheric component uses a Cartesian grid that extends from 20 solar radii to (TBD) solar radii. There is some overlap of the SC and IH grids at their interface to support the coupling of the solar corona and inner heliosphere components. Both grids employ adaptive mesh refinement to increase the resolution near the heliospheric current sheet.
The only input required from the user is to select the Carrington Rotation from the drop down menu.
All other configuration parameters are pre-selected. The PARAM.in file determines the detailed specification of this configuration. It is posted along with the results. To interpret this file, please refer to the manual.
Outputs include the MHD plasma parameters (atomic mass unit density N, pressure P, velocity V_x, V_y, V_z, magnetic field B_x, B_y, B_z, electric currents, J_x, J_y, J_z, Alfven wave energy densities I01, I02 and dissipation rates GammaLperp, GammaCref. Description of derived variables can be found here.
The above quantities are available in full 3D, in 2D slices, as well as along satellite orbits.
COMING SOON: The model can produce synthetic images of the Sun's atmosphere, including EUV, X-ray and white-light images.
For a detailed description of these components in the SWMF and the 3D codes used:
I. Sokolov et al., Magnetohydrodynamic Waves and Coronal Heating: Unifying Empirical and MHD Turbulence Models, Astrophysical Journal, 764, 23 (2013)
G. Toth et al, Journal of Computational Physics, Volume 231, 870 (2012)
G. Toth, B. van der Holst & Z. Huang, Obtaining Potential Field Solution with Spherical Harmonics and Finite Differences, Astrophysical Journal, 732, 102, (2011)
References and relevant publications
B. van der Holst et al., Alfven Wave Solar Model (AWSoM): Coronal Heating, Astrophysical Journal, 782:81 (2014)
Model Developers Manual