Joint Astrophysics Colloquium

Fingering convection in geophysics and Astrophysics

Pascale Garaud

University of California at Sant Cruz

Double-diffusive instabilities can occur in fluids where both heat and chemical composition control the buoyancy of the fluid. If these two components diffuse at different rates, an instability can occur even if the density is stably stratified. The fluid is then rapidly mixed by small scale convective motions. Interestingly, secondary instabilities of the turbulent convection can then occur, which excites very large-scale motions, such as internal gravity waves or lateral intrusions. Another spectacular outcome of the double-diffusion if the formation of persistent large-scale "staircases" in the density, temperature and chemical composition profiles.

Here, we present the first self-consistent theory for the development of large-scale double-diffusive instabilities, compare them against high-resolution and large-domain numerical simulations, and finally, discuss their impact in the oceanographic context and in astrophysics.