Thermal boundary condition at the planetary tangent cylinder

Ascertain the actual thermal boundary condition along the tangent cylinder in Earth’s outer core and characterize its dynamical consequences; specifically, determine whether the tangent-cylinder boundary behaves effectively as adiabatic—yielding horizontal isothermal surfaces across the cylinder—or effectively as isothermal—producing strong baroclinicity and a sidewall-driven flow—and quantify the resulting impact on polar rotating convection and heat transfer in tangent-cylinder geometries.

Background

In rapidly rotating planetary cores, the Taylor–Proudman constraint separates the polar region inside the tangent cylinder (TC) from the equatorial region outside it. Accurately modeling the TC in laboratory experiments is essential to reproduce polar rotating convection and its coupling to the rest of the core.

The authors emphasize that the thermal boundary condition at the TC is both unknown and crucial for the flow: an adiabatic boundary would maintain horizontal isothermal surfaces across the cylinder, whereas an isothermal boundary would induce strong baroclinicity and drive a flow near the TC’s sidewall. Since planetary TC conditions are unlikely to match either ideal case exactly, identifying the effective thermal boundary condition is necessary to interpret experiments and to constrain polar convection in Earth’s core.