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Modèle numérique du couplage thermo-chimique entre le manteau et la graine


IPGP - Campus Jussieu


Ateliers des Fluides Géologiques

Salle Bleue



Evidence for departures from axial symmetry in the time-average fluid dynamics of the Earth's outer core is found in the non-axial structure of the time-average paleomagnetic field, the persistent asymmetric large-scale core flows imaged by geomagnetic secular variation, and observations of lateral seismic heterogeneity near the top of the inner core. Here we present results of a numerical dynamo model showing that these features are connected through a single mechanism, large-scale flows in the outer core that couple the heterogeneity of the inner core with that of the lower mantle. Thermo-chemical convection in our model is driven by an heterogeneous core-mantle boundary heat flow condition based on a thermal interpretation of lower mantle seismic tomography. The main feature of the time-average outer core flow is a cyclonic circulation below Asia that extends from the core-mantle boundary to the surface of the inner core. This thermo-chemical wind concentrates magnetic field on the core-mantle boundary at the observed location, locally agrees with core flow images, and produces anomalously high rates of light element release in the eastern hemisphere of the inner core boundary, suggesting that lateral seismic anomalies at the top of the inner core result from mantle-induced lateral variations in its freezing rate. ---------------------------------------------------------------------- Atelier des Fluides Géologiques ----------------------------------------------------------------------