Oscillatory double-diffusive convection in a rotating spherical shell at low Rayleigh numbers

Yue-Kin Tsang (Newcastle University)

Wednesday 20th November 15:00-16:00 Maths 311B

Abstract

We consider a fluid whose density depends on two scalar quantities with very different diffusivities (e.g. temperature and salinity). If the two scalars give rise to opposing buoyancy forces, instabilities may occur in counter-intuitively manners. In this talk, we focus on the setup that the fast-diffusing scalar tends to destabilise the system while the slow-diffusing one is stabilising (e.g. warm and more salt at the bottom). This regime is sometimes known as oscillatory double-diffusive convection (ODDC). Motivated by situations in the interiors of gas giants and stars, we investigate ODDC in a rotating spherical shell. Our fully nonlinear numerical simulations show that the inclusion of a presumably stabilising scalar can promote the onset of convection in the presence of rotation. Moreover, diverse flow patterns are found in the long-time statistically steady state. Theoretically, we extend Busse's approach (1986) in capturing the essential physics of the spherical system using a cylindrical annulus model. By disentangling the different linear modes in this model, we explain qualitatively the interesting features found in the spherical shell.

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