Interannual Magneto-Coriolis modes and their sensitivity on the magnetic field within the Earth's core
arxiv(2024)
摘要
Linear modes for which the Coriolis acceleration is almost entirely in
balance with the Lorentz force are called Magneto-Coriolis (MC) modes. These MC
modes are thought to exist in Earth's liquid outer core and could therefore
contribute to the variations observed in Earth's magnetic field. The background
state on which these waves ride is assumed here to be static and defined by a
prescribed magnetic field and zero flow. We introduce a new computational tool
to efficiently compute solutions to the related eigenvalue problem, and study
the effect of a range of both axisymmetric and non-axisymmetric background
magnetic fields on the MC modes. We focus on a hierarchy of conditions that
sequentially partition the numerous computed modes into those which are (i) in
principle observable, (ii) those which match a proxy for interannual
geomagnetic signal over 1999-2023, and (iii) those which align with core-flows
based on recent geomagnetic data. We found that the background field plays a
crucial role in determining the structure of the modes. In particular, we found
no examples of axisymmetric background fields that support modes consistent
with recent geomagnetic changes, but that some non-axisymmetric background
fields do support geomagnetically consistent modes.
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