Text of Solar Surface Dynamics convection & waves Bob Stein - MSU Dali Georgobiani - MSU Dave Bercik - MSU...
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
The solar atmosphere is dynamic, But we dont apply that knowledge. Static models are overly simplistic & give an inaccurate picture.
Observed Dynamics: Granulation white light image
P-Mode Oscillations Doppler velocity image
Magnetic Coronal Loops Emission traces magnetic field lines
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.
Chromospheric Temperature: hot or cold Get enhanced emission without enhanced gas temperature, because source function preferentially samples high temperatures.
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
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
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
Wave Reflection Acoustic Wave Gravity wave
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.
Simplifications Only 5 rays 4 Multi-group opacity bins Assume L C
Opacity is binned, according to its magnitude, into 4 bins.
Line opacities are assumed proportional to the continuum opacity Weight = number of wavelengths in bin
Wavelengths with same (z) are grouped together, so integral over and sum over commute Advantage integral over and sum over commute
Advantage Wavelengths with same (z) are grouped together, so integral over and sum over commute
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
Energy Fluxes ionization energy 3X larger energy than thermal
Fluid Parcels reaching the surface Radiate away their Energy and Entropy Z S E Q
Entropy Green & blue are low entropy downflows, red is high entropy upflows Low entropy plasma rains down from the surface
Plasma cooled at surface is pulled down by gravity
A Granule is a fountain velocity arrows, temperature color
Stratified convective flow: diverging upflows, turbulent downflows Velocity arrows, temperature fluctuation image (red hot, blue cool)
Vorticity Downflows are turbulent, upflows are more laminar.
Velocity at Surface and Depth Horizontal scale of upflows increases with depth.
Stein & Nordlund, ApJL 1989
Upflows are slow and have nearly the same velocity.
Upflows diverge. Fluid reaching surface comes from small area below the surface
Downflows are fast. In 9 min some fluid reaches the bottom.
Downflows converge. Fluid from surface is compressed to small area below surface
Vorticity surface and depth.
Velocity Distribution Up Down
Vorticity Distribution Down Up
Magnetic Field Reorganization
Simulation Results: B Field lines
Field Distribution simulation observed Both simulated and observed distributions are stretched exponentials.
Flux Emergence & Disappearance
Emerging Magnetic Flux Tube
Magnetic Field Lines, t=0.5 min
Magnetic Field Lines, t=1.0 min
Magnetic Field Lines, t=1.5 min
Magnetic Field Lines, t=2.0 min
Magnetic Field Lines, t=2.5 min
Magnetic Field Lines, t=3.0 min
Magnetic Field Lines, t=3.5 min
Magnetic Field Lines, t=4.0 min
Magnetic Field Lines, t=4.5 min
Magnetic Field Lines, t=5.0 min
Magnetic Field Lines, t=5.5 min
Magnetic Field Lines: t=6 min
Magnetic Flux Tube Fieldlines
Flux Tube Evacuation V xz + B
Flux Tube Evacuation field lines + density fluctuations
Micropores David Bercik - Thesis
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
Micropore Intensity image + B contours @ 0.5 kG intervals (black) + V z =0 contours (red).
Flux Tube Evacuation field + temperature contours
Flux Tube Evacuation field + density contours
Comparison with Observations
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
Line Profiles Line profile without velocities. Line profile with velocities. simulation observed
Convection produces line shifts, changes in line widths. No microturbulence, macroturbulence. Average profile is combination of lines of different shifts & widths. average profile
Stokes Profiles of Flux Tube new SVST, perfect seeing
Stokes Profiles of Micropore intensity + slit
Spectrum of granulation Simulated intensity spectrum and distribution agree with observations after smoothing with telescope+seeing point spread function.