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Helioseismology Simulations: Analysis and Results from MSU and NBI Collaborations

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snowy
25 diapositives · 402 Views · Sep 05, 2014

This presentation shares results from simulations conducted by Bob Stein (MSU) and Åke Nordlund (NBI, Denmark), with contributions from David Benson (Kettering University). Utilizing a staggered mesh and non-linear numerical methods, we investigate the dynamics of solar subsurface flows. The simulations cover a domain of 96 x 96 x 20 Mm, with detailed grid resolutions and multiple variables analyzed. We aim to validate various techniques in solar physics and helioseismology while providing datasets for future research. For further details, explore the archived datasets or contact the team.

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  1. Data forHelioseismology Testing Dali Georgobiani Michigan State University Presenting the results of Bob Stein (MSU) & Åke Nordlund (NBI, Denmark) with David Benson (Kettering University) Stanford, July 29, 2008

  2. Numerical Method Staggered mesh Non-linear, fully compressible, 3D, explicit Spatial differencing: 6th order centered finite difference Time advancement: 3rd order Runge-Kutta

  3. Size and Resolution • Size of the domain: 96 Mm x 96 Mm x 20 Mm 1000 x 1000 x 500 grid points • Grid information: dx = dy = 0.1 Mm dz = 0.012–0.075 Mm dt = 0.25 sec (saved every 60 sec)

  4. Mean Atmosphere

  5. Vertical Velocity at 2.5 & 8 Mm depth Boxes show domain of earlier simulations at 6, 12, 24 & 48 Mm widths.

  6. Vertical momentum at 0, 2, 4, 16 Mm

  7. Vertical momentum vs depth

  8. Velocity stream lines Courtesy Chris Henze (NASA)

  9. Finite time Lyapunov exponent (proxy for vorticity) Courtesy Bryan Green (AMTI/NASA)

  10. Available Datasets Simulated data are being ingested into the new SDO JSOC database • Website http://sha.stanford.edu/stein_sim (some info) • Contact Bob Stein stein@pa.msu.edu (more info) Thanks to Rick Bogart for his extensive help with archiving!

  11. Archived Data Description • 9 variables: horizontal velocities Vx, Vz, vertical velocity Vy, temperature, density, pressure, internal energy, electron density, and G1 • Each snapshot of a variable is stored in a separate file; 9 variables at each time step are combined to be retrieved together • Data are in FITS format • Duration 511 minutes (360 minutes recorded, WIP) • A snapshot of a variable occupies approximately 2 GB of disk space • First and third directions are horizontal, second direction is vertical • Vertical grid is provided separately (The data will be available for retrieval soon – check with Rick)

  12. Another Data Set • 4 hour averages, with 2 hour overlap • 6 variables: horizontal velocities Vx, Vz, vertical velocity Vy, temperature, density, and sound speed • Simultaneous surface velocities • Stored in the IDL SAVE format at MSU • Work in progress… initial 6 variables calculated and stored, now adding internal energy E

  13. Units of Variables • Length is in 108 cm = 1 Mm • Time is in 102 s • Velocities Vx, Vz, and Vy are in 10 km/s • Temperature is in K • Density is in 10-7 g/cm3 • Pressure is in 105 dynes/cm2 • Internal energy is in 105 ergs/cm3 • Electron density is log cm-3

  14. Data Analysis • Power spectrum • Tests of time-distance methods Compare the results for the simulations and the SOHO/MDI high-res observations (211.5 Mm by 211.5 Mm patch, 512 min) The following work was performed with Junwei Zhao and Alexander Kosovichev

  15. Power Spectra Simulations MDI high-res data

  16. Power Spectra Simulations Hinode data

  17. Velocity Spectra sqrt [k P(k)]

  18. Time-Distance Diagram

  19. TD Diagrams at Various Depths

  20. Exploring Simulated Surface Structures • Spatial filtering • Spectral analysis • f-mode time-distance analysis • Local correlation tracking

  21. Large Structures

  22. Time-Distance Analysis

  23. Horizontal Flow Fields Simulations Inversions Depth range is 2-3 Mm. The longest arrow corresponds to 300 m/s

  24. Local Correlation Tracking Correlation coefficient Is 0.99 But velocity amplitudes are under- estimated (~1.8 times lower than in simulations)

  25. Conclusions These simulations provide an excellent opportunity to validate various techniques, widely used in solar physics and helio- seismology for directly obtaining otherwise inaccessible properties (subsurface flows, structures etc.) On the other hand, these analysis techniques also help to examine how realistic the simulations are