“Waves in the Earth's Core”Jeremy BloxhamProfessor of Geophysics and Chair Abstract Observations of the Earth’s magnetic field made at or above the Earth’s surface reveal a rich spectrum of field behavior, from the chaotic record of magnetic reversals on timescales of millions of years to abrupt, localized changes in the field on timescales as short as a year. In this talk we consider how to dissect this record in order to gain insight into the dynamical processes in the core responsible for the generation and and evolution of the magnetic field. In the atmosphere, considerable understanding has come from identifying wave phenomena; similarly in the core we expect a number of wave phenomena to exist. In order to identify waves in the core it is necessary first to remove the effects of the background convective flow. When that is done, a particular class of waves known as torsional oscillations are revealed, as first shown by Stephen Zatman. The combination of the nearly steady background convective flow and torsional oscillations describes a large part of the behavior of the field over timescales of several centuries, including, rather unexpectedly, abrupt, localized changes in the field. This dynamical picture of the core also provides us with a useful tool for addressing such questions as the complexity of the field at the core-mantle boundary, providing evidence that the field there is considerably more complex than previously imaged.
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