Turbulent convective length scale in planetary cores

Area of Science:

• Geophysics
• Fluid Dynamics
• Planetary Science

Background:

• Convection in planetary fluid cores transports heat and chemical species, driving planetary magnetic fields.
• Accurate modeling of core convection is challenging due to dependencies on rotation, buoyancy, and magnetic fields.
• Rapidly rotating turbulent convection in non-magnetic cores is a poorly understood regime.

Purpose of the Study:

• To explore the regime of rapidly rotating turbulent convection in planetary cores.
• To determine the key factors controlling convective length scales in planetary cores.
• To develop more realistic models for small, non-magnetic planetary cores and extrapolate to larger ones.

Main Methods:

• Utilized non-magnetic numerical models to simulate rapidly rotating turbulent convection.
• Investigated the dependence of convective length scale on viscosity, flow velocity, and planetary rotation.
• Applied findings to model the dynamics of small non-magnetic cores and extrapolate to larger planetary bodies.

Main Results:

• Convective length scale becomes independent of viscosity under realistic planetary core conditions.
• The length scale is primarily determined by flow velocity and planetary rotation.
• For Earth's core, the turbulent convective length scale is approximately 30 km, significantly larger than the viscous scale.

Conclusions:

• The turbulent convective length scale provides a lower limit for energy-carrying scales in core flows.
• This finding simplifies geodynamo simulations by potentially relaxing the need to resolve the viscous scale.
• The study offers a more realistic approach to modeling convection in small non-magnetic cores like the Moon and allows extrapolation to larger cores.