Planetary Core-Style Rotating Convective Flows in Paraboloidal Laboratory Experiments

Turbulent convection in a planet's outer core is simulated here using a thermally-driven, free surface paraboloidal laboratory annulus. We show that the rapidly rotating convection dynamics in free-surface paraboloidal annuli are similar those in planetary spherical shell geometries. Three experimental cases are carried out, respectively, at 35 revolutions per minute (rpm), 50 and 60 rpm. Thermal Rossby waves are detected in full disk thermographic images of the fluid's free surface. Ultrasonic flow velocity measurements reveal the presence of multiple azimuthal (zonal) jets, with successively more jets forming in higher rotation rate cases. The jets' cylindrical radial extent is well approximated by the Rhines scale. Over time, the zonal jets migrate to larger radial position with migration rates in good agreement with prior theoretical estimates. Our results suggest that planetary core rotating convection will be comprised of flow structures found in other turbulent geophysical fluid dynamical systems: convective turbulence dominates the small-scale flow field, and also act to flux energy into larger-scale, slowly evolving zonal flow structures. How the ambient magnetic fields in planetary core settings affect such turbulent flows remains an open question.

Automated summary

This study simulates turbulent convection in a planet's outer core using a thermally-driven, free surface paraboloidal laboratory annulus. The researchers found that the dynamics of rapidly rotating convection in free-surface paraboloidal annuli are similar to those in planetary spherical shell geometries. The experiments showed the presence of thermal Rossby waves and multiple azimuthal jets, with more jets forming at higher rotation rates. The migration of the jets and the flux of energy into larger-scale zonal flow structures were also observed. The effects of ambient magnetic fields on such turbulent flows remain unknown.