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Planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the Earth's core surface | | N Gillet
; D Jault
; C. C. Finlay
; | | Date: |
29 Feb 2016 | | 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. | | Source: | arXiv, 1602.9094 | | Services: | Forum | Review | PDF | Favorites | |
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