Geoid and topographic profiles over constant-viscosity thermal plumes in spherical-axisymmetric geometry at moderate Rayleigh numbers are compared with results from previous studies in other geometries. Plumes in spherical-axisymmetric models produce larger geoid anomalies than plumes in either Cartesian or cylindrical-axisymmetric geometries; however, the topographic anomalies over the plumes are smaller than the corresponding anomalies in a cylindrical-axisymmetric geometry but larger than those in a Cartesian geometry. For plumes in a temperature-dependent viscosity fluid, the geoid and topographic profiles are reduced by a factor of two when compared to a constant viscosity fluid with the same background viscosity profile. In this case, the radially-averaged temperature profile around the plume creates a low-viscosity ‘layer’ beneath the lithosphere.
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