Planetary Auroras are one indication of a magnetic dipole field
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Internal Dynamo in a Liquid Core Generates the Main Planetary Magnetic Field
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Planetary Data
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(Some) Geodynamo Researchers
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Interior of the Earth
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The Earth’s Inner Core
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Geological Record: Geomagnetic Excursions
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Basic Equations Mathematical model based on the magnetohydrodynamic (MHD) equations with buoyancy → the 'Boussinesq approximation : compositional variation is not included because of strong mixing.
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Numerical Modeling Solve nonlinear partial differential equations (PDEs) on computer. Various methods: finite difference, finite volume,.... For regular geometries, we can choose a spectral method
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Geodynamo Parameters
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Magnetic Fields Turbulent relaxation of ideal magneto-fluid
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Spectral Method Model
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Spherical Harmonics
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Function Expansions for Spherical Shells
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Coefficients = Dynamical Variables
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A Dynamical System The spectral method tums a few PDEs into many coupled ODES
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Statistics of Ideal MHD Turbulence
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Probability Density Function (PDF) The invariants for ideal MHD are
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Expectation Values
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Cross Helicity, HC He is essentially the cross correlation between velocity and magnetic field in the liquid core.
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Expected Dipole Angle 0 vs Cross Helicity Hc The dipole angle can be calculated using the statistical theory, with maximum , i, m = 100 Large-scale numerical simulations of ideal, rotating MHD turbul…
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Summary: The Ideal MHD Geodynamo
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Conclusion
Description:
Explore the fascinating world of planetary dynamos in this comprehensive lecture. Delve into the mechanisms behind planetary magnetospheres and auroras, indicators of magnetic dipole fields. Examine the internal dynamo processes occurring in liquid cores that generate main planetary magnetic fields. Study planetary data and learn about key geodynamo researchers. Investigate the Earth's interior structure, including its inner core, and analyze the geological record of geomagnetic excursions. Understand the basic equations and mathematical models based on magnetohydrodynamic (MHD) equations with buoyancy. Discover numerical modeling techniques for solving nonlinear partial differential equations, including spectral methods for regular geometries. Explore geodynamo parameters, magnetic fields, and turbulent relaxation of ideal magneto-fluid. Learn about spherical harmonics, function expansions for spherical shells, and the transformation of PDEs into coupled ODEs. Examine the statistics of ideal MHD turbulence, probability density functions, and invariants. Investigate cross helicity and its relationship to the expected dipole angle. Gain insights into large-scale numerical simulations of ideal, rotating MHD turbulence in spherical shells and their implications for effective cross helicity.
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