Appears in collection : 2026 - T2 - WS2 - Instabilities and transitions in geophysical flows

We study double-diffusive convection in the case of an unstable compositional gradient in the presence of a stabilising temperature gradient. Experimental and analytical studies (Hage and Tilgner 2010; Schmitt 2011) have shown that narrow salt fingers (usually encountered in thermohaline convection in “bottom-heavy” layers) can be preferred over large-scale convection in the regime where the stable temperature gradient is much smaller than the destabilising compositional gradient (the “top-heavy” regime). Here, we extend this problem to the context of planetary cores using hydrodynamical numerical simulations in a rotating spherical shell at low Prandtl number. We show that fingering convection can also be preferred over overturning compositional convection for both weak and strong rotation across large regions of parameter space and the transition between the two regimes of convection is gradual.

Co-authors: Martin Gray, Graeme Sarson