A01 Planetary Core Dynamics, Dynamos and Fundamental MHD Processes (Div. I)

IAGA (Aeronomy, Geomagnetism)

23-Jun-2015, 13:30 - 15:00

Abstract content:

Double-buoyancy convection in rotating spherical shells.

Earth's core is a rotating convective system where buoyancy forces arise due to variations in density due to both temperature and composition. From a geophysical point of view, these two buoyancy-providing fields are very different in nature: they diffuse at vastly different rates, they require different boundary conditions, and they have different sinks and sources. Thus, it is expected that their interaction and competition of may lead to substantially novel dynamics. To gain insight into this problem we consider the linear onset and the finite-amplitude properties of convection of a rotating fluid in a spherical shell driven by thermal and compositional buoyancy forces. Even in the case when the thermal and compositional components differ only by the values of their diffusivity we find that the surface of neutral stability describing the onset of convection in the double-buoyancy case is essentially different from that of the well-studied purely thermal case. In particular, an additional ‘‘double-diffusive’’ eigen-mode becomes dominant in certain regions of the parameter space and necessitates up to three values of the critical Rayleigh number to describe the onset of convection. Furthermore, convection is possible at both collinear and counter-linear orientations of the thermal and compositional buoyancy, and these cases may be of some geophysical relevance. We report systematic parameter studies of the amplitude, the spatial and temporal features of non-linear double-buoyancy convection and explore the possibility of stratification near the outer spherical surface.

L. Silva1, R. Simitev1.
1University of Glasgow, School of Mathemathics and Statistics, Glasgow, United Kingdom.


Double-buoyancy convection     Numerical simulation     Stratification