Dynamos with weakly convecting outer layers: implications for core-mantle boundary interaction

Sreenivasan, Binod; Gubbins, David

doi:10.1080/03091920801900047

Cited by 35 publications

(26 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Some of the parameters are far from the values thought to be correct for the Earth, but the same is true for all numerical geodynamo models [except perhaps for the large Roberts number, a limitation that might be removed in future work by changing the buoyancy profile (Sreenivasan and Gubbins, 2008)]. This means we must be cautious in what we compare with observation.…”

mentioning

confidence: 75%

Time-averaged paleomagnetic field and secular variation: Predictions from dynamo solutions based on lower mantle seismic tomography

Davies

Gubbins

Willis

et al. 2008

Physics of the Earth and Planetary Interiors

Self Cite

View full text Add to dashboard Cite

We compare 3 dynamo solutions incorporating laterally varying boundary heat flux with paleomagnetic models and data. The boundary condition is defined by the D seismic shear wave velocity and the 3 solutions have boundary anomalies with different amplitudes. The generated fields appear to divide into a stationary, boundary-locked part and a time-varying part with persistent centres of activity. Both parts contribute to the time average. A very Page 2 of 32 A c c e p t e d M a n u s c r i p t long averaging time can be needed for nearly-locked solutions, but a rough time average that remains within the threshold set by the accuracy of paleomagnetic data is achieved in a few diffusion times. The locked part dominates for larger amplitude boundary anomalies.In previous work the locked field was shown to have strong similarities with the modern geomagnetic field. Previous dynamo solutions that were not locked to the boundary show similarities with our solutions with weak boundary forcing. The axisymmetric time average has small g 0 2 and larger g 0 3 components and peaks in inclination anomaly in high latitudes (associated with the locked field) and low latitudes (associated with the time average of the time-varying fields). The non-axisymmetric time average displays a striking longitudinal variation in inclination anomaly, with a large negative anomaly in the Pacific region in agreement with observations. None of the dominant geomagnetic coefficients are axisymmetric and g 0 2 negligible in all 3 models. Secular variation is concentrated in equatorial latitudes, as in some recent paleomagnetic models. The locked field agrees with the inclination difference found between Hawai'i and Réunion, in agreement with paleomagnetic averages. The locked field agrees with the paleomagnetic time average rather better than the fields with less boundary variations. We conclude that, because the locked field agrees with the modern field as well as some aspects of the long-term time average, the geomagnetic field spends a considerable time in the present 4-lobe configuration: it is not a coincidence that the present field resembles the time average. Longitudinal variations are likely to be at least as important as latitudinal variations in the paleomagnetic time average. This presents a challenge for dynamo theory, since a move to more geophysically realistic parameters would appear to destroy the locked solutions.

show abstract

mentioning

confidence: 75%

Time-averaged paleomagnetic field and secular variation: Predictions from dynamo solutions based on lower mantle seismic tomography

Davies

Gubbins

Willis

et al. 2008

Physics of the Earth and Planetary Interiors

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is achieved by suppressing convection in the outer regions through a volumetric heat sink so that boundary-driven thermal winds are allowed to balance the Coriolis forces. [The thermodynamic implications of a heat sink in a model of Boussinesq convection are discussed in Sreenivasan & Gubbins (2008).] The above regime could be relevant to the Earth's dynamo because the departure from equipartition does allow the magnetic energy, E m to be greater than the kinetic energy, E k .…”

Section: Discussionmentioning

confidence: 99%

“…5 of a recent paper by the author (Sreenivasan & Gubbins, 2008). While the flow is dominated by the two downwellings, convection rolls tend to migrate towards φ = ±π/2 and clump together near these longitudes.…”

Section: Force Balances In Lockingmentioning

confidence: 99%

On dynamo action produced by boundary thermal coupling

Sreenivasan

2009

Physics of the Earth and Planetary Interiors

Self Cite

View full text Add to dashboard Cite

Please cite this article as: Sreenivasan, B., On dynamo action produced by boundary thermal coupling, Physics of the Earth and Planetary Interiors (2008), doi:10.1016/j.pepi.2009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Page 1 of 32 A c c e p t e d M a n u s c r i p t and magnetic fields. The departure from equipartition in a partially locked dynamo allows the magnetic energy to be greater than the kinetic energy. As the balance of forces in a locked dynamo is different from that in a convection-driven dynamo, lower-mantle coupling could have a marked effect on the structure and dynamics of convection in the Earth's core.

show abstract

“…The thickest layers are predicted to coincide with the time of maximum surface heat flow, although this result depends on the timescale for variations in the surface heat flow. The existence of a stratified layer in the core might be inferred from observations of variations in the magnetic field, because a stable layer would filter magnetic fluctuations from the underlying convective region (Sreenivasan and Gubbins, 2008). Distinctive features in the field may also develop in the stratified layer through interactions with the convective flow in the underlying region (Zhang and Schubert, 2000).…”

mentioning

confidence: 99%

Core–Mantle Interactions

Buffett

2015

Treatise on Geophysics

View full text Add to dashboard Cite

Dynamos with weakly convecting outer layers: implications for core-mantle boundary interaction

Cited by 35 publications

References 26 publications

Time-averaged paleomagnetic field and secular variation: Predictions from dynamo solutions based on lower mantle seismic tomography

Time-averaged paleomagnetic field and secular variation: Predictions from dynamo solutions based on lower mantle seismic tomography

On dynamo action produced by boundary thermal coupling

Core–Mantle Interactions

Contact Info

Product

Resources

About