Planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the Earth's core surface

Abstract

We report a calculation of time-dependent quasi-geostrophic core flows for 1940-2010. Inverting recursively for an ensemble of solutions, we evaluate the main source of uncertainties, namely the model errors arising from interactions between unresolved core surface motions and magnetic fields. Temporal correlations of these uncertainties are accounted for. The covariance matrix for the flow coefficients is also obtained recursively from the dispersion of an ensemble of solutions. Maps of the flow at the core surface show, upon a planetary-scale gyre, time-dependent large-scale eddies at mid-latitudes and vigorous azimuthal jets in the equatorial belt. The stationary part of the flow predominates on all the spatial scales that we can resolve. We retrieve torsional waves that explain the length-of-day changes at 4 to 9.5 years periods. These waves may be triggered by the nonlinear interaction between the magnetic field and sub-decadal non-zonal motions within the fluid outer core. Both the zonal and the more energetic non-zonal interannual motions were particularly intense close to the equator (below 10 degrees latitude) between 1995 and 2010. We revise down the amplitude of the decade fluctuations of the planetary scale circulation and find that electromagnetic core-mantle coupling is not the main mechanism for angular momentum exchanges on decadal time scales if mantle conductance is 3 10 8 S or lower.

References in corpus (6)

• Forward and adjoint quasi-geostrophic models of the geomagnetic secular variation
• Hydromagnetic quasi-geostrophic modes in rapidly rotating planetary cores
• The dynamics and excitation of torsional waves in geodynamo simulations
• On the reflection of Alfvén waves and its implication for Earth's core modeling
• Variability modes in core flows inverted from geomagnetic field models
• Bayesian inversion for the filtered flow at the Earth's Core Mantle Boundary

Cited by in corpus (20)

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• Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics
• The interplay of fast waves and slow convection in geodynamo simulations nearing Earth's core conditions
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• Dynamic regimes in planetary cores: τ-{\ell} diagrams
• Characterisation of hydromagnetic waves propagating over a steady, non-axisymmetric background magnetic field