AN EXPERIMENTAL APPROACH TO THERMOCHEMICAL CONVECTION IN THE EARTHS CORE

Both thermal and compositional buoyancy affect convection in the Earth's liquid outer core. We report preliminary experiments on the structure of thermochemical convection in a rotating sphere with the geometry of the Earth's core. Fully-developed thermochemical convection in a rapidly rotating sphere is driven by buoyant ribbon-shaped plumes concentrated in the equatorial region. Curtains of fluid aligned parallel to the rotation axis and extending across the sphere move with the plumes. The motion is turbulent in planes parallel to the equator. The convection generates a secondary, large scale zonal flow which is primarily retrograde (westward). The main difference between chemically-dominated and thermally-dominated convection is the smaller scales of motion present when compositional buoyancy drives the flow. In cases when both are present simultaneously, the probable situation in the outer core, we find the structure of the motion is similar to purely thermal convection.