Planetary gyre, time‐dependent eddies, torsional waves, and equatorial jets at the Earth's core surface. Issue 6 (3rd June 2015)

• Record Type: Journal Article
• Authors: Gillet, N.; Jault, D.; Finlay, C. C.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 6(2015:Jun.)
• Page Start: 3991
• Page End: 4013
• Publication Date: 2015-06-03
• Subjects: core flow -- secular variation -- torsional waves -- equatorial dynamics -- stochastic equations; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2014JB011786
• Languages: English
• ISSNs: 2169-9313

Abstract

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 midlatitudes, 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 subdecadal nonzonal motions within the fluid outer core. Both the zonal and the more energetic nonzonal interannual motions were particularly intense close to the equator (below 10 ∘ 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. Key Points: We image time changes of core flows using a stochastic approach We extend the detection of torsional waves to 1940–2010 We detect intense equatorial jets at latitudes below 10 degrees