Definition, Scope, and Aims
The Earth is not a perfect timekeeper, and the spectrum of the variations in the mantle’s angular velocity \( \hat{\boldsymbol{\Omega}} \) spans a wide range of frequencies. Of particular interest here are the comparatively large amplitude decadal and semidecadal variations in which changes in length of day, P, of up to 2 ms occur. These would not be explained even if the global circulations of the atmosphere and oceans could be reversed. This is confirmed by a more detailed argument given in our recent review (Roberts and Aurnou 2012), which will be referred to here as “RA12.”
The origin of these length of day (LOD) variations must be sought in the Earth’s core, and Fig. 1 suggests that the task is not an easy one. Fig. 1b shows dP/dt, derived by differentiating smoothed LOD data from the last half century, with atmospheric, oceanic, and tidal signals removed; semi-decadal time variations are clearly seen with a period τLODof about 6 years (e.g., Abarca...
This is a preview of subscription content, log in via an institution.
Bibliography
Abarca del Rio R, Gambis R, Salstein DA (2000) Interannual signals in length of day and atmospheric angular momentum. Ann Geophys 18:347–364
Alboussière T, Deguen R, Melzani M (2010) Melting induced stratification above the Earth’s inner core due to convective translation. Nature 466:744–747
Anufriev AP, Braginsky SI (1975) Influence of irregularities of the boundary of the Earth’s core on the velocity of the liquid and on the magnetic field. Geomagn Aeron 15:754–757
Anufriev AP, Braginsky SI (1977a) Influence of irregularities of the boundary of the Earth’s core on the fluid velocity and the magnetic field, II. Geomagn Aeron 17:78–82
Anufriev AP, Braginsky SI (1977b) Influence of irregularities of the boundary of the Earth’s core on the fluid velocity and the magnetic field, III. Geomagn Aeron 17:742–750
Braginsky SI (1970) Torsional magnetohydrodynamic vibrations in the Earth’s core and variations in day length. Geomagn Aeron 10:1–8
Braginsky SI (1984) Short-period geomagnetic secular variation. Geophys Astrophys Fluid Dyn 30:1–78
Braginsky SI (1999) Dynamics of the stably stratified ocean at the top of the core. Phys Earth Planet Inter 111:21–34
Braginsky SI, Roberts PH (1995) Equations governing convection in Earth’s core and the geodynamo. Geophys Astrophys Fluid Dyn 79:1–97
Braginsky SI, Roberts PH (2007) Anelastic and Boussinesq approximations. In: Gubbins D, Herrero-Bervera E (eds) Encyclopedia of geomagnetism and paleomagnetism. Springer, Heidelberg, pp 11–19
Brito D, Aurnou JM, Cardin P (2004) Turbulent viscosity measurements relevant to planetary core-mantle dynamics. Phys Earth Planet Inter 141:3–8
Buffett BA (1996) Gravitational oscillations in the length of day. Geophys Res Lett 23:2279–2282
Buffett BA (1997) Geodynamic estimates of the viscosity of the Earth’s inner core. Nature 388:571–573
Buffett BA (1998) Free oscillations in the length of day: inferences on physical properties near the core-mantle boundary. Geodynamics 28:153–165
Buffett BA (2010) Chemical stratification at the top of Earth’s core: constraints from nutation observations. Earth Planet Sci Lett 296:367–372
Buffett BA, Christensen UR (2007) Magnetic and viscous coupling at the core-mantle boundary; inferences from observations of the Earth’s nutations. Geophys J Int 171:145–152
Buffett BA, Glatzmaier GA (2000) Gravitational braking of inner-core rotation in geo-dynamo simulations. Geophys Res Lett 27:3125–3128
Buffett BA, Mathews PM, Herring TA (2002) Modeling of nutation and precession: effects of electromagnetic coupling. J Geophys Res 107:2070. https://doi.org/10.1029/2000JB000056
Buffett BA, Mound J, Jackson A (2009) Inversion of torsional oscillations for the structure and dynamics of Earth’s core. Geophys J Int 177:878–890
Dai W, Song X (2008) Detection of motion and heterogeneity in Earth’s liquid outer core. Geophys Res Lett 35:L16311
Davidson PA (2001) An introduction to magnetohydrodynamics. Cambridge University Press, Cambridge, UK
Davidson PA (2004) Turbulence. Oxford University Press, Oxford, UK
de Wijs GA, Kresse G, Vocadlo I, Dobson DP, Alfèe D, Gillan MJ, Price GD (1998) The viscosity of liquid iron at the physical conditions of Earth’s core. Nature 392:805–807
Defraigne P, Dehant V, Wahr J (1996) Internal loading of an inhomogeneous compressible mantle with phase boundaries. Geophys J Int 125:173–192
Deleplace B, Cardin P (2006) Viscomagnetic torque at the core-mantle boundary. Geophys J Int 167:557–566
Dobson DP, Crichton WA, Vočadlo I, Jones AP, Wang Y, Uchida T, Rivers M, Sutton S, Brodhardt JP (2000) In situ measurements of viscosity of liquids in the Fe-FeS system at high pressures and temperatures. Am Mineral 85:1838–1842
Dormy E, Roberts PH, Soward AM (2007) Core, boundary layers. In: Gubbins D, Herrero Bervera E (eds) Encylopedia of geomagnetism and paleomagnetism. Springer, Heidelberg, pp 111–116
Dumberry M (2007) Taylor’s constraint and torsional oscillations. In: Cardin P, Cugliandolo LF (eds) Dynamos. Elsevier, Amsterdam, pp 383–401
Dumberry M (2010) Gravity variations induced by core flows. Geophys J Int 180:635–650
Dumberry M, Mound J (2008) Constraints on core-mantle electromagnetic coupling from torsional oscillation normal modes. J Geophys Res 113:B03102. https://doi.org/10.1029/2007JB005135
Elsasser WM (1946) Induction effects in terrestrial magnetism, II. The secular variation. Phys Rev 70:202–212
Fearn DR, Loper DE, Roberts PH (1981) Structure of the Earth’s inner core. Nature 292:232–233
Finlay CC, Dumberry M, Chulliat A, Pais MA (2010) Short timescale core dynamics: theory and observations. Space Sci Rev 155:177–218. https://doi.org/10.1007/s11214-010-9691-6
Forte AM, Woodward RJ, Dziewonski AM (1994) Joint inversion of seismic and geo-dynamic data for models of three dimensional mantle heterogeneity. J Geophys Res 99:21857–21877
Gargett AE (1984) Vertical eddy diffusivity in the ocean interior. J Mar Res 42:359–393
Gillet N, Jault D, Canet E, Fournier A (2010) Fast torsional waves and strong magnetic field within the Earth’s core. Nature 465(7294):74–77. https://doi.org/10.1038/nature09010
Glatzmaier GA, Roberts PH (1995) A three-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle. Phys Earth Planet Inter 91:63–75
Goldreich PM, Mitchell JL (2010) Elastic ice shells and synchronous moons: implications for cracks on Europa and non-synchronous rotation on Titan. Icarus. https://doi.org/10.1016/j.icarus.2010.04.013
Gross RS (2001) A combined length-of-day series spanning 1832–1997: LUNAR97. Phys Earth Planet Inter 123:65–76
Gross RS (2007) Earth rotation variations – long period. In: Herring TA (ed) Physical geodesy. Treatise on geophysics, vol 3. Elsevier, Oxford, pp 239–294
Gross RS (2009) Ocean tidal effects on Earth rotation. J Geodyn 48:219–225
Heimpel MH, Aurnou JM (2007) Turbulent convection in rapidly rotating spherical shells: a model for equatorial and high latitude jets on Jupiter and Saturn. Icarus 187:540–557
Hide R (1969) Interaction between the Earth’s liquid core and solid mantle. Nature 222:1055–1956
Hide R (1998) A note on topographic core-mantle coupling. Phys Earth Planet Inter 109:91–92
Hide R, James IN (1983) Differential rotation produced by potential vorticity mixing in a rapidly rotating fluid. Geophys J R Astron Soc 74:301–312
Hide R, Clayton RW, Hager BH, Speith MA, Voorhies CV (1993) Topographic core-mantle coupling and fluctuations in Earth’s rotation. In: Aki K, Dmowska R (eds) Relating geophysical structures and processes: the Jeffreys volume. Geophysical monograph series, vol 76. AGU, Washington, DC, pp 107–120
Holme R (1998) Electromagnetic core-mantle coupling-I. Explaining decadal changes in the length of day. Geophys J Int 132:167–180
Holme R, de Viron O (2005) Geomagnetic jerks and a highresolution length-of-day profile for core studies. Geophys J Int 160:435–439
Hulot G, Eymin C, Langlais B, Mandea M, Olsen N (2002) Small-scale structure of the geodynamo inferred from Oersed and Magsat satellite data. Nature 416:620–623
Jackson A (1997) Time-dependency of tangentially geostrophic core surface motions. Phys Earth Planet Inter 103:293–311
Jackson A (2003) Intense equatorial flux spots on the surface of Earth’s core. Nature 424:760–763
Jacobs JA (1953) The Earth’s inner core. Nature 172:297–298
Jault D (2003) Electromagnetic and topographic coupling, and LOD variations. In: Jones CA, Soward AM, Zhang K (eds) Earth’s core and lower mantle. Taylor and Francis, London, pp 46–76
Jault D, Le Mouël JL (1989) The topographic torque associated with a tangentially geostrophic motion at the core surface and inferences on the flow inside the core. Geophys Astrophys Fluid Dyn 48:273–296
Jault D, Le Mouël JL (1999) Comment on ‘On the dynamics of topographic core-mantle coupling’ by Weijia Kuang and Jeremy Bloxham. Phys Earth Planet Inter 114:211–215
Jault D, Gire C, LeMouel J-L (1988) Westward drift, core motions and exchanges of angular momentum between core and mantle. Nature 333:353–356
Kawai K, Tsuchiya T (2009) Temperature profile in the lowermost mantle from seismological and mineral physics joint modeling. Proc Natl Acad Sci U S A. https://doi.org/10.1073/pnas.0905920106
Kuang W-J, Bloxham J (1993) The effect of boundary topography on motions in the Earth’s core. Geophys Astrophys Fluid Dyn 72:161–195
Kuang W-J, Bloxham J (1997) On the dynamics of topographic core-mantle coupling. Phys Earth Planet Inter 99:289–294
Kuang W-J, Chao BF (2001) Topographic core-mantle coupling in geodynamo modeling. Geophys Res Lett 28:1871–1874
Loper DE (2007) Turbulence and small-scale dynamics in the core. In: Olson PL (ed) Core dynamics. Treatise on geophysics, vol 8. Elsevier, Amsterdam, pp 187–206
Love JJ, Bloxham J (1994) Electromagnetic coupling and the toroidal magnetic field at the core-mantle boundary. Geophys J Int 117:235–256
Margot JL, Peale SJ, Jurgens RF, Slade MA, Holin IV (2007) Large longitude libration of Mercury reveals a molten core. Science 316:710–714
Mathews PM, Herring TA, Buffett BA (2002) Modeling of nutation and precession: new nutation series for nonrigid Earth and insights into the Earth’s interior. J Geophys Res 107:2068. https://doi.org/10.1029/2001JB000390
Monnereau M, Calvet M, Margerin L, Souriau A (2010) Lopsided growth of Earth’s inner core. Science 328:1014–1017
Morse SA (1986) Adcumulus growth of the inner core. Geophys Res Lett 13:1466–1469
Mound JE, Buffett BA (2003) Interannual oscillations in length of day: implications for the structure of the mantle and core. J Geophys Res 108:2334. https://doi.org/10.1029/2002JB002054
Mound JE, Buffett BA (2005) Mechanisms of core-mantle angular momentum exchange and the observed spectral properties of torsional oscillations. J Geophys Res 110:B08103. https://doi.org/10.1029/2004JB003555
Mound J, Buffett B (2006) Detection of a gravitational oscillation in length-of-day. Earth Planet Sci Lett 243:383–389
Müller U, Bühler L (2001) Magnetofluiddynamics in channels and containers. Springer, Heidelberg
Noir J, Hemmerlin F, Wicht J, Baca SM, Aurnou JM (2009) An experimental and numerical study of librationally driven flow in planetary cores and subsurface oceans. Phys Earth Planet Inter 173:141–152
Ohta K, Onada S, Hirose K, Sinmyo R, Shimizu K, Saya N, Ohishi Y, Yasuhara A (2008) The electrical conductivity of post-perovskite in Earth’s D″ layer. Science 320:89–91
Olsen N, Mandea M (2008) Rapidly changing flows in the Earth’s core. Nat Geosci 1:390–394
Roberts PH, Aurnou JM (2012) On the theory of core-mantle coupling. Geophys Astrophys Fluid Dyn (to appear)
Roberts PH, Soward AM (1972) Magnetohydrodynamics of the Earth’s core. Annu Rev Fluid Mech 4:117–154
Roberts PH, Yu ZJ, Russell CT (2007) On the 60-year signal from the core. Geophys Astrophys Fluid Dyn 43:321–330
Rogers TM, Glatzmaier GA (2006) Angular momentum transport by gravity waves in the solar interior. Geophys Astrophys Fluid Dyn 653:756–764
Schubert G, Turcotte DL, Olson P (2001) Mantle convection in the earth and planets. Cambridge University Press, Cambridge, UK
Sprague M, Julien K, Knobloch E, Werne J (2006) Numerical simulation of an asymptotically reduced system for rotationally constrained convection. J Fluid Mech 551:141–174
Stellmach S, Hansen U (2004) Cartesian convection driven dynamos at low Ekman number. Phys Rev E 70:056312
Stix M, Roberts PH (1984) Time-dependent electromagnetic core-mantle coupling. Phys Earth Planet Inter 36:49–60
Tanaka S (2010) Constraints on the core-mantle boundary topography from P4KP-PcP differential travel times. J Geophys Res 115:B04310. https://doi.org/10.1029/2009JB006563
Taylor JB (1963) The magnetohydrodynamics of a rotating fluid and the Earth’s dynamo problem. Proc R Soc Lond A274:274–283
Tyler RH (2008) Strong ocean tidal flow and heating on moons of the outer planets. Nature 456:770–773
Uno H, Johnson CL, Anderson BJ, Korth H, Solomon SC (2009) Modeling Mercury’s internal magnetic field with smooth inversions. Earth Planet Sci Lett 285:328–339
Velicogna I, Wahr J (2006) Acceleration of Greenland ice mass loss in spring 2004. Nature 443:329–331
Vočadlo I, Alfè D, Price GD, Gillan MJ (2000) First principles calculation of the diffusivity of FeS at experimentally accessible conditions. Phys Earth Planet Inter 120:145–152
Wahr J, de Vries D (1989) The possibility of lateral structure inside the core and its implications for nutation and Earth tide observations. Geophys J Int 99:511–519
Wahr J, Swenson S, Velicogna I (2006) Accuracy of GRACE mass estimates. Geophys Res Lett 33:L06401. https://doi.org/10.1029/2005GL025305
Wicht J, Christensen UR (2010) Torsional oscillations in dynamo simulations. Geophys J Int 181:1367–1380
Yoshida S, Sumita I, Kumazawa M (1996) Growth model of the inner core coupled with outer core dynamics and the resulting elastic anisotropy. J Geophys Res 101:28085–28103
Yoshino T (2010) Laboratory electrical conductivity measurement of mantle minerals. Surv Geophys 31:163–206. https://doi.org/10.1007/s10712-009-9084-0
Acknowledgments
We thank Richard Gross, Richard Holme, and Andrew Jackson for sharing their insights and their data. We are also grateful to Bruce Buffett and the referee (Mathieu Dumberry) for giving helpful advice.
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2020 Springer Nature Switzerland AG
About this entry
Cite this entry
Roberts, P.H., Aurnou, J.M. (2020). Core-Mantle Coupling. In: Gupta, H. (eds) Encyclopedia of Solid Earth Geophysics. Encyclopedia of Earth Sciences Series. Springer, Cham. https://doi.org/10.1007/978-3-030-10475-7_39-1
Download citation
DOI: https://doi.org/10.1007/978-3-030-10475-7_39-1
Received:
Accepted:
Published:
Publisher Name: Springer, Cham
Print ISBN: 978-3-030-10475-7
Online ISBN: 978-3-030-10475-7
eBook Packages: Springer Reference Earth and Environm. ScienceReference Module Physical and Materials ScienceReference Module Earth and Environmental Sciences