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