HR: 0830h
AN: S21E-0378    [PDF]
TI: An Andersonian Theory of Earth's Outer Core
AU: * Loper, D E
EM: loper@gfdi.fsu.edu
AF: Florida State University, GFDI-4360, Tallahassee, FL 23206 United States
AB: Conventional wisdom holds that the geodynamo operating in Earth's core is in a state of vigorous turbulent convective motion. This talk presents an alternative model in which the motions are vigorous but not turbulent. Turbulence in the outer core is inhibited by three independent effects. First, the Coriolis force inhibits motions which are not invariant in the direction of the rotation axis. Second, the Lorentz force quickly dampens motions which are not invariant in the direction of the magnetic field. Third, the conduction of heat down the (nearly) adiabatic temperature gradient causes material to cool as it descends, thereby becoming stably stratified. It follows that motions in the outer core must be directly driven, either by buoyant material rising from the inner core boundary (ICB) or dense material descending from the core-mantle boundary (CMB). It will be shown that the ICB is more a more likely source of motions than the CMB. Vigorous convection driven by sources of buoyancy at a boundary invariably consists of narrow rapid motions away and broad slow motions toward the boundary. It is plausible that buoyant fluid leaves the ICB, either in the form of continuous plumes or discrete parcels, at preferred locations and rises through an otherwise quiescent outer core. The possible forms of these plumes and parcels will be surveyed, and their ability to sustain the geodynamo will be investigated.
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Seismology [S]
MN: 2003 Fall Meeting