Fingers refers to narrow, tube-like streams of fluid that move upward or downward inside the planetary core.
The study uses hydrodynamical simulations within a rotating spherical shell geometry to model fingering convection, by solving the Boussinesq approximation of the Navier-Stokes equations. The equations are solved using a pseudo-spectral method. Variables are expanded in spherical harmonics for the angular components and a second-order finite difference scheme is used for the radial direction.
The ratio of the squared buoyancy frequency to the squared rotation rate is calculated here. It indicates the relative importance of buoyancy (vertical stratification) versus rotation (Coriolis forces) in a fluid system.
Rotation changes the direction and shape of the fingers:
When the planetary core rotates very fast, the Coriolis force becomes more important than buoyancy. As a result fingers no longer rise straight up/down (radially), instead they align with the rotation axis, forming long columns. This creates powerful east-west flowing zonal winds inside the core.
Intermediate regimes: These are highly anisotropic and drift slowly towards the equator over time.
Weakly-Rotating Regime: The fingers align with gravity and the mixing becomes more homogeneous laterally, causing the strong zonal flows to weaken and eventually disappear.
When the stratification is very strong, the fingers group together into small clusters, and only weak, slow changes in density appear on large scales. These density patterns are surrounded by big, donut-shaped circulating flows (toroidal gyres) in the upper part of the layer. This may affect the magnetic field.
This helps for study of the Mercury core.
Source: https://arxiv.org/html/2511.11442v1
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