A thermo-chemical wind coupling the Earth''s inner core and deep mantle

The time-average dynamical processes occurring in the Earth''s fluid outer core are thought to depart from axial symmetry, as suggested by models of the paleomagnetic field at the core-mantle-boundary, by time-average core flows derived from the secular variation of the geomagnetic field, and by seismic maps of heterogeneity at the top of the solid inner core. Here we show that these three observations can be explained by the existence of a steady thermo-chemical wind connecting the Earth''s core-mantle and inner core boundaries. We use a numerical model of core dynamics and dynamo action driven by thermo- chemical convection. On top of the simulation shell, we impose a positive heat flow anomaly below China, consistent with deep-mantle seismic tomography, and its interpretation in terms of thermal versus chemical origins. This drives a columnar cyclone below Asia, locally concentrating the radial magnetic field into a persistent flux patch. The cyclone also permanently brings cold and chemically depleted material close to the inner-core-boundary, causing the inner core to crystallize at a faster pace below the Eastern hemisphere. Future progresses in inner-core seismology should allow to test a possible heterogeneity between the northern and southern hemispheres of the inner core, as predicted by our model.