Solar Surface Dynamics convection & waves Bob Stein - MSU Dali Georgobiani - MSU Dave Bercik - MSU Regner Trampedach - MSU Aake Nordlund - Copenhagen Mats

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  • Solar Surface Dynamics convection & waves Bob Stein - MSU Dali Georgobiani - MSU Dave Bercik - MSU Regner Trampedach - MSU Aake Nordlund - Copenhagen Mats Carlsson - Oslo Viggo Hansteen - Oslo Andrew McMurry - Oslo Tom Bogdan - HAOO
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  • The solar atmosphere is dynamic, But we dont apply that knowledge. Static models are overly simplistic & give an inaccurate picture.
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  • Observed Dynamics: Granulation white light image
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  • P-Mode Oscillations Doppler velocity image
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  • Magnetic Coronal Loops Emission traces magnetic field lines
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  • Waves: what is observable Tgas (dashed), Trad (solid) Horizontal lines are means, which preferentially sample high temperatures because source function is non-linear function of temperature.
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  • Chromospheric Temperature: hot or cold Get enhanced emission without enhanced gas temperature, because source function preferentially samples high temperatures.
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  • Proton density: Equilibrium (dashed), Non-equilibrium (solid)
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  • Shocks: Ionization & Recombination
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  • Mean Atmosphere Inhomogeneous T (see only cool gas), P turb Raises atmosphere 1 scale height
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  • Never See Hot Gas
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  • Simulations
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  • Two Calculations 1. 3D, compressible, mhd 2. 1D, non-LTE radiation hydro-dynamics
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  • Computation Solve Conservation equations mass, momentum & internal energy Induction equation Radiative transfer equation 3D, Compressible EOS includes ionization Open boundaries Fix entropy of inflowing plasma at bottom
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  • Equations
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  • Method Spatial derivatives - Finite difference 6 th order compact or 3 rd order spline Time advance - Explicit 3 rd order predictor-corrector or Runge-Kutta Diffusion
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  • Boundary Conditions Periodic horizontally Top boundary: Transmitting Large zone, adjust < mass flux, u/z=0, energy constant, drifts slowly with mean state Bottom boundary: Open, but No net mass flux (Node for radial modes so no boundary work) Specify entropy of incoming fluid at bottom (fixes energy flux) Top boundary: B potential field Bottom boundary: inflows advect 1G or 30G horizontal field, or B vertical
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  • Wave Reflection Acoustic Wave Gravity wave
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  • Radiation Transfer LTE Non-gray - multigroup Formal Solution Calculate J - B by integrating Feautrier equations along one vertical and 4 slanted rays through each grid point on the surface.
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  • Simplifications Only 5 rays 4 Multi-group opacity bins Assume L C
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  • Opacity is binned, according to its magnitude, into 4 bins.
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  • Line opacities are assumed proportional to the continuum opacity Weight = number of wavelengths in bin
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  • Wavelengths with same (z) are grouped together, so integral over and sum over commute Advantage integral over and sum over commute
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  • Advantage Wavelengths with same (z) are grouped together, so integral over and sum over commute
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  • Initial Conditions Snapshot of granular convection (6x6x3 Mm) Resolution: 25 km horizontally, 15-35 km vertically 1G or 30G horizontal seed field, or 400 G vertical field, imposed
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  • Solar Magneto-Convection
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  • Energy Fluxes ionization energy 3X larger energy than thermal
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  • Fluid Parcels reaching the surface Radiate away their Energy and Entropy Z S E Q
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  • Entropy Green & blue are low entropy downflows, red is high entropy upflows Low entropy plasma rains down from the surface
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  • Plasma cooled at surface is pulled down by gravity
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  • A Granule is a fountain velocity arrows, temperature color
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  • Stratified convective flow: diverging upflows, turbulent downflows Velocity arrows, temperature fluctuation image (red hot, blue cool)
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  • Vorticity Downflows are turbulent, upflows are more laminar.
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  • Velocity at Surface and Depth Horizontal scale of upflows increases with depth.
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  • Stein & Nordlund, ApJL 1989
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  • Upflows are slow and have nearly the same velocity.
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  • Upflows diverge. Fluid reaching surface comes from small area below the surface
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  • Downflows are fast. In 9 min some fluid reaches the bottom.
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  • Downflows converge. Fluid from surface is compressed to small area below surface
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  • Vorticity surface and depth.
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  • Turbulent downdrafts
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  • Velocity Spectrum
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  • Velocity Distribution Up Down
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  • Entropy Distribution
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  • Vorticity Distribution Down Up
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  • Magnetic Field Reorganization
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  • Simulation Results: B Field lines
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  • Field Distribution simulation observed Both simulated and observed distributions are stretched exponentials.
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  • Exponential Distribution
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  • Flux Emergence & Disappearance
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  • Emerging Magnetic Flux Tube
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  • Magnetic Field Lines, t=0.5 min
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  • Magnetic Field Lines, t=1.0 min
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  • Magnetic Field Lines, t=1.5 min
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  • Magnetic Field Lines, t=2.0 min
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  • Magnetic Field Lines, t=2.5 min
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  • Magnetic Field Lines, t=3.0 min
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  • Magnetic Field Lines, t=3.5 min
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  • Magnetic Field Lines, t=4.0 min
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  • Magnetic Field Lines, t=4.5 min
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  • Magnetic Field Lines, t=5.0 min
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  • Magnetic Field Lines, t=5.5 min
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  • Magnetic Field Lines: t=6 min
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  • Magnetic Flux Tube Fieldlines
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  • Flux Tube Evacuation V xz + B
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  • Flux Tube Evacuation field lines + density fluctuations
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  • Micropores David Bercik - Thesis
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  • Strong Field Simulation Initial Conditions Snapshot of granular convection (6x6x3 Mm) Impose 400G uniform vertical field Boundary Conditions Top boundary: B -> potential field Bottom boundary: B -> vertical Results Micropores
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  • Micropore Intensity image + B contours @ 0.5 kG intervals (black) + V z =0 contours (red).
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  • Flux Tube Evacuation field + temperature contours
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  • Flux Tube Evacuation field + density contours
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  • Comparison with Observations
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  • Observables
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  • Solar velocity spectrum MDI doppler (Hathaway) TRACE correlation tracking (Shine) MDI correlation tracking (Shine) 3-D simulations (Stein & Nordlund) v ~ k v ~ k -1/3
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  • Line Profiles Line profile without velocities. Line profile with velocities. simulation observed
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  • Convection produces line shifts, changes in line widths. No microturbulence, macroturbulence. Average profile is combination of lines of different shifts & widths. average profile
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  • Stokes Profiles of Flux Tube new SVST, perfect seeing
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  • Stokes Profiles of Micropore intensity + slit
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  • Granulation
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  • Spectrum of granulation Simulated intensity spectrum and distribution agree with observations after smoothing with telescope+seeing point spread function.
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  • Granule Statistics
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  • Magnetic Field & Granules
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  • Emergent Intensity, mu=0.5
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  • Magnetic Field Strength
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