Effect of depth‐dependent viscosity on the pattern of mantle convection

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Abstract
Three‐dimensional structures of thermal convection are studied by numerical experiments in a rectangular domain of a plane fluid layer. The main question is the joint effect of the heating mode and the depth‐dependent viscosity on the planform of the circulation. Heating mode is defined by the ratio of internal and basal heat inputs. For viscosity‐depth functions, simple models of the mantle viscosity are used. If the Rayleigh number is of the order 105–106 (based on the maximum viscosity), this choice produces cellular flow with a closed network of cold descending sheets around isolated upwellings, independently of the heating mode. The central upwellings are concentrated in narrow cylindrical plumes if there is a significant basal heat input. Convection of the Earth's mantle may occur with descending currents represented by subduction and ascending currents in the form of plumes situated below hotspots.