Models of convection in Earth’s core with lateral variations in boundary heat flow

Dr. Christopher Davies (University of Leeds)

Thursday 19th November, 2015 14:00-15:00 Maths 326

Abstract

The problem of thermally driven convection in a rapidly rotating spherical shell with homogeneous boundary conditions has been widely studied owing to its application to planetary cores. The dynamics of this system are determined by the Rayleigh number Ra, measuring the strength of the thermal driving force, the Prandtl number Pr, the ratio of viscous and thermal diffusion, and the Ekman number E, measuring the strength of the Coriolis force. The main challenges are to understand the behaviour of the system in the limits of small E and high Ra that characterise many core regions. An important modification to this homogeneous problem in the geophysical context is the addition of lateral variations in heat-flux at the outer boundary with amplitude measured by the nondimensional parameter q*, the ratio of peak-to-peak heat-flux variations on the boundary to the average outer boundary heat-flux. I will give an overview of the fluid dynamical problem in the context of Earth’s liquid core and then present models of rapidly rotating convection in a spherical shell with Pr=1 and E = 0.00001. These models employ values of q*=2-10 and Rayleigh numbers up to 400 times the critical value for the onset of homogeneous convection that are approaching current estimates appropriate to Earth’s core. I will compare homogeneous (q*=0) and inhomogeneous solutions in terms of their spatio-temporal behaviour and heat transfer properties. I will also investigate the extent to which the effects of heat-flux anomalies imposed at the outer boundary penetrate into the deep interior of the shell.

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