Approaching a realistic force balance in geodynamo simulations.

Area of Science:

• Geophysics
• Plasma Physics
• Computational Fluid Dynamics

Background:

• Earth's magnetic field is generated by a dynamo process in the liquid outer core.
• Geodynamo simulations often require high viscosity, leading to concerns about accurately representing core physics.
• Theoretical models predict a balance between magnetic, Archimedean, and Coriolis forces (MAC balance) in the core.

Purpose of the Study:

• To investigate if MAC balance can be achieved in geodynamo simulations with reduced viscosity.
• To analyze the relative strengths of forces governing fluid motion in the Earth's core.
• To determine if simulations with realistic force balances better reflect geodynamo physics.

Main Methods:

• Performed geodynamo simulations with viscosity reduced to near practical limits.
• Directly analyzed the forces (Lorentz, Coriolis, buoyancy, viscous, inertial) acting within the simulated core fluid.
• Compared simulation results with non-magnetic convection at identical parameters.

Main Results:

• Achieved MAC balance with Lorentz, buoyancy, and Coriolis forces of similar magnitude.
• Viscous and inertial forces were found to be at least 20 times weaker than dominant forces in the bulk fluid.
• Dynamo flow exhibited larger scales and reduced geostrophy compared to non-magnetic convection.
• Heat transport by convection doubled in the presence of strong Lorentz force influence.

Conclusions:

• Geodynamo simulations can achieve MAC balance, reflecting more realistic core physics.
• Reduced viscosity simulations demonstrate the dominant role of Lorentz forces in geodynamo processes.
• These findings improve our understanding of Earth's magnetic field generation and core dynamics.