SLIDE 1
Fully Convective Dynamos in Rapidly Rotating Regimes
- Liquid Cores of Rocky Planets
- Giant Planets with Deep Convection Zones
- Low Mass M Dwarfs
- Red Giant He Burning Cores
- Cores of Main-Sequence Intermediate and High Mass Stars
The Magnetic Furnace: Examining Fully Convective Dynamos and the - - PowerPoint PPT Presentation
The Magnetic Furnace: Examining Fully Convective Dynamos and the - - PowerPoint PPT Presentation
The Magnetic Furnace: Examining Fully Convective Dynamos and the Influence of Rotation Fully Convective Dynamos in Rapidly Rotating Regimes Liquid Cores of Rocky Planets Giant Planets with Deep Convection Zones Low Mass M Dwarfs
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SLIDE 3
Questions Potentially Addressed with Global-Scale Simulations What differences arise between HD and MHD?
Impact for 1-D models
How do a greater luminosity and a changing rotation impact a dynamo?
+ Magnetostrophyand possible Rossby number scaling + Sensitivities of core dynamo models to diffusion e.g. Low-Pm vs. High-Pm
Can superequipartition states be sustained? What are the limiting behaviors of the system?
How superequipartitioncan they become?!
SLIDE 4
- Consider a statistically steady state with the following force balance
for a non-rotating system:
- Further, let
- Then, the equipartition magnetic field should roughly be
Some Simple Considerations for Scaling Laws
⇢v·rv ⇡ 1 4⇡ r⇥B⇥B. Let them be as `v = Pm`B. 4⇡`B `v ⇢v2 ⇡ B2 = ) Beq ⇡ 4⇡⇢v2 Pm 1/2
SLIDE 5
- Extend this statistically-steady force balance to a rotating system:
- Then, the super-equipartition magnetic field may scale as
Some Simple Considerations for Scaling Laws
SLIDE 6
- An alternative approach from Davidson 2013: the MAC Balance
- Or
- Predicts that super-equipartition magnetic field may scale as
Some Simple Considerations for Scaling Laws
1/2
SLIDE 7
−2.0 −1.5 −1.0 −0.5
0.0 0.5 1.0 1.5 2.0 log10 Ro−1
−1.0 −0.5
0.0 0.5 1.0 1.5 log10 ME/KE (a)
Some Simple Considerations for Scaling Laws
Augustson et al. 2016 Yadav et al. 2016
SLIDE 8
ASH (Anelastic Spherical Harmonic) code
‒Parallel pseudospectralcode ‒Spherical harmonic & Chebyshev
- r Finite-difference decomposition
‒Semi-implicit time-stepping ‒Realistic stratification ‒Including a stratified stable layer ‒Magnetism
The ASH Code
Clune et al. 1999; Miesch et al. 2000; Brun et al. 2004
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Energy Flux and Convective Dynamics
SLIDE 10
Magnetic Fields and Their Energy
SLIDE 11
Magnetic Fields and Their Energy
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Superequipartition Across Resolved Scales
Augustson et al. 2016
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How can such states exist?
In these simulations, displacement of magnetic and velocity fields minimizes Lorentz forces on heat-carrying flows.
Strong-Field Initial Condition Weak-Field Initial Condition
SLIDE 14
How can such states exist?
The displaced fields have weak generation, while generation occurs largely in the overlap regions, namely at the edges of the magnetic structures. So how might the magnetic structures propagate?
Featherstone et al. 2009
SLIDE 15
How can such states exist?
Regions of increasing velocity and magnetic field magnitudes are increasing aligned, regulating field generation
SLIDE 16
How can such states exist?
The velocity field adjusts to minimize the work done by Lorentz forces.
SLIDE 17