Abstract:
We report the results of thermal convection experiments in a rapidly rotating hemispherical shell with a heterogeneous heat flux at the outer boundary to model the effect of a thermally heterogeneous core-mantle boundary on the convection in the Earth's outer core. A parameter study is made by varying the heat flux, size, and location of an anomalously heated patch for a range of Rayleigh numbers at ∼108 and a fixed Ekman number 4.7 × 10−6. Experiments show that fully developed, boundary-driven convection occurs when the radial convective heat transfer from the heater exceeds that of the surrounding boundary region. The flow consists of a large-scale cyclonic circulation originating from the heater and includes a radially extending spiralling front with a jet. The front is stationary when the sectorial high heat flux region is imposed at low latitudes but becomes unstable when it is imposed at high latitudes. The ratio of applied heat which is partitioned to radial and lateral heat transfer becomes fixed in this regime. Measurements also indicate that there is a close correlation between the flow direction and the statistics of temperature fluctuations. Applied to the Earth, the experiments suggest that there are two scales of flows in the core: fine-scaled jets and slower, large-scale flows. The large-scale hemispherical structure of the core can be interpreted in terms of the boundary-driven flow driven by the high heat flow region beneath east Asia.
