Coupling of mantle temperature anomalies and the flow pattern in the core: interpretation based on simple convection calculations

Abstract

The association of some relatively stationary features of the magnetic field at the core-mantle boundary (CMB) with temperature anomalies in the deep mantle inferred from seismic tomography has led to the speculation that flow in the core is locked to thermal anomalies in the mantle, with downwellings (upwellings) in the core lying below cold (hot) anomalies in the lower mantle (Bloxham and Gubbins). The relatively large temperature anomalies in the mantle act to control the heat flux out of the core, with high heat flux into colder than average mantle and low (perhaps negative) heat flux into regions of hotter than average mantle. We use a simple two-dimensional, internally heated convection model in a Cartesian geometry with varying thermal boundary conditions to investigate this problem. The relationship between upwellings (downwellings) and maxima (minima) in surface heat flux depends upon the thermal boundary condition, with maximum heat flux sometimes associated with upwellings, sometimes downwellings, and sometimes neither. However, for moderate Rayleigh numbers, large aspect ratio geometries and large variations in heat flux, the Bloxham and Gubbins hypothesis is supported.