HR: 1340h
AN: MR43A-0877    [Abstracts]
TI: Time-Average Core Flow: Mantle vs. Core Origins
AU: * Amit, H
EM: hagay@jhu.edu
AF: Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218 United States
AU: Olson, P
EM: olson@jhu.edu
AF: Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218 United States
AB: We derive a time-average surface core flow by inverting geomagnetic secular variation data over a century. We use a grid-based numerical method with a helical-geostrophic assumption for the tangential velocity divergence to invert the frozen flux induction equation for the fluid flow below the core-mantle boundary at specific epochs. Those flows are then combined to form time-average and time-dependent parts. We compare our time-average core flow with two models of thermal wind flow. The first model is thermal wind driven by density gradients associated with convection in the core and a homogeneous core-mantle boundary. This model is obtained from numerical dynamo simulations. The second model is thermal wind driven by density gradients associated with core-mantle thermal coupling, without core convection. This model is obtained using lower mantle seismic tomography for the density gradients. Our results suggest that, over century time scales, only the zonal part of the flow at the top of the core may be considered steady. We find equatorially asymmetric zonal core flow at low and mid latitudes, consistent with an origin by thermal coupling to lower mantle heterogeneity. In contrast, at high latitudes, the time average zonal core flow consists of westward polar vortices, which are more consistent with an origin by core convection.
DE: 1507 Core processes (8115)
DE: 1515 Geomagnetic induction
DE: 1560 Time variations--secular and long term
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting