Fluid Dynamics in Earth and Planetary Sciences (FDEPS) Second FDEPS Workshop Dec 04 - Dec 08, 2000 Graduate School of Mathematical Sciences, University of Tokyo
Core-mantle thermal interaction
YOSHIDA, Shigeo (Department of Earth and Planetary Sciences, Nagoya Univ.)
It is important to obtain information in the Earth's core for the understanding of the dynamics in the Earth's deep interior. However, our knowledge about the flow is still limited due to the lack of direct observations. The most important observations about the flow is the geomagnetic field, because the field is generated by a fluid motion of the liquid iron in the outer core. The information is, however, limited because what we can observe is the field pattern only on the surface of the core. This limitation leads to the idea that we would obtain important information about the core flow in terms of core-mantle coupling, because we have seismological observations about the mantle convection. The thermal effect of the mantle on the core can be a clue to the understanding of the outer core flow. The geomagnetic field has components which are stationary relative to the mantle for a long time. This indicates core-mantle interactions, because the field pattern would drift eastwards or westwards if the mantle did not influence the core flow. Stationary features should be considered as a sign of core-mantle interactions. They should allow us to obtain information about the flow through comparison of the geomagnetic field with the seismic tomography of the mantle. We still do not have basic theories for the thermal core-mantle interaction. What we are working on is the construction of the linear theory of thermal response. I will mainly present the linear response theory of the core fluid to thermal heterogeneities on the core-mantle boundary in this talk. The main focus is the simplest case of non-mangetic, neutrally stable fluid without a basic flow. I will mainly talk about the result for a sectorial temperature distribution on the core-mantle boundary. The solutions for the linear theory can be categorized into two regimes depending on the Ekman number E. The boundary between the fast rotation regime and the slow rotation regime is about E=1/100. The slow rotation regime can be understood by a perturbation to the non-rotationg case. The fast rotation regime can be understood by the superposition of the Ekman layer, the equatorial modified Ekman layer, and the Stewartson layer on the thermal wind solution.