Supergranulation-Scale Solar Convection Simulations
David Benson, Michigan State University, USA
Robert Stein, Michigan State University, USA
Aake Nordlund, Astronomical Observatory, NBIfAFG, Denmark
AGU - SPD Conference May, 2005 New Orleans, LA
Overview
• Purpose
• Computational Methodology (brief)
• Methods for Initializing Simulations
• Preliminary Results: Simulations In-Progress 50Mm x 50Mm x 20Mm (deep) simulations Relaxing thermally and dynamically
• Future Directions
Significance and Questions1. Second Helium Ionization Zone
• Separate the role of second helium ionization zone from the effect of the increasing scale height with depth
2. Helioseismology• Simulations serve as a tool for analyzing local helioseismic inversion techniques
3. Nature of the Surface Shear Layer
4. Development and Maintenance of the Magnetic Network
Computational Domain
• 50Mm x 50Mm x 20Mm
• 5003 grid points
• Grid clustering near visible surface
50 Mm
50 M
m
20 M
m
Computational Domain for the CFD Simulations of Solar Convection
Numerical Method• Spatial differencing
– 6th-order centered f.d.– staggered
• Time advancement– 3rd order Runga-Kutta
• Equation of state– tabular – including ionization– H, He + abundant elements
• Radiative transfer– 3D, LTE– 4 bin opacity distrib. fxn
• Quenching
Computational Information
• Fortran 90• Parallelized - OpenMP
– single parallel region
• Michigan State University – 64 processor Altix
• NCSA– IBM P690
• NASA Ames– Altix (128 processors)
Objective:
layer MPI on top of the OpenMP
Initialization Methods24 Mm and 12 Mm Simulations
• 12 Mm simulation (9 Mm deep)• well-relaxed• extended adiabatically to 20 Mm
• Relax dynamics 12 Mm -- 20 Mm deep• Create 24 Mm wide box - and relax the following
1. 12 Mm stretched to 24Mm• generates large scale structure
2. 12 Mm doubled to 24 Mm
Initialization MethodsConstruction of 50 Mm Initial State
1. Stretch 12 Mm x 20 Mm to 50 Mm• Generates large scale structure• Breaks symmetry
2. Stretch 24 Mm x 20 Mm to 50 Mm• Generates intermediate level structure
3. Quadruple 12 Mm x 20 Mm to 50 Mm• Produces small scale structure
Combine & RelaxCombine & Relax
Initialization SnapshotsComponents + Composite : Uz at 0.25 Mm
Snapshots of methods + composite (?)
Initialization SnapshotsComponents + Composite : Uz at 17.3 Mm
Mean Atmosphere StateTemperature, Density and Pressure
Mean Atmosphere StateIonization of H and He
Energy FluctuationNeed for Relaxation
Future Research Direction
• Relax hydrodynamic simulations (further)
• Implement magnetic field boundary conditions and add Coriolis force terms
• Results will be available to help in answering questions about ...
• Maintenance of magnetic network• f-plane rotation -- Coriolis force• Local helioseismic inversion techniques