Large-Scale Flow in the Core

Holme, Richard

doi:10.1016/b978-044452748-6.00127-9

Cited by 137 publications

(189 citation statements)

References 82 publications

Supporting

Mentioning

180

Contrasting

Unclassified

Order By: Relevance

“…2 shows the structure of the inferred jet in 2015 defined with M = 1, which is described by just three unknown coefficients and has associated optimal δ = 0.12 (in dimensional units 420 km). The jet has a maximum velocity of about 40 km yr −1 , twice the speed of the equatorial flux patches of 18 km yr −1 [9], and three times the typical rms speed of 13 km yr −1 from globalscale core-flow inversions [21]. This jet is confined in longitude and so it is neither circumpolar nor zonal, despite being predominantly azimuthal.…”

Section: Observationally-constrained High-latitude Flowmentioning

confidence: 99%

See 1 more Smart Citation

An accelerating high-latitude jet in Earth’s core

2016

View full text Add to dashboard Cite

Observations of the change in Earth's magnetic field, the secular variation, provide information on the motion of liquid metal within the core that is responsible for its generation. The very latest high-resolution observations from ESA's Swarm satellite mission show intense field change at high-latitude localised in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we explain this feature with a localised, non-axisymmetric, westwards jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core.We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km/yr, and is now much stronger than typical large-scale flows inferred for the core. The current accelerating phase may be a part of a longer term fluctuation of the jet causing both eastwards and westwards movement of magnetic features over historical

show abstract

Section: Observationally-constrained High-latitude Flowmentioning

confidence: 99%

“…where u H denotes the horizontal flow [21]. We prescribe δ and M and fit the resulting 2M + 1 modal coefficients by minimising the target residual defined over both northern (N) and southern (S) regions…”

Section: Observationally-constrained High-latitude Flowmentioning

confidence: 99%

An accelerating high-latitude jet in Earth’s core

2016

View full text Add to dashboard Cite

show abstract

“…Using Earth's rotation rate of = 0.729 × 10 −4 s −1 in the numerical calculations gives a root-mean-square (rms) velocity of about 0.037 mm yr −1 . This value is about an order of magnitude smaller than the rms velocity, V rms = 0.38 mm s −1 , inferred from coresurface flow (Holme 2015). By adjusting the rotation rate in the model to = 7.383 × 10 −4 s −1 we produce an rms velocity that matches the core-surface flow.…”

Section: Time Dependence Of Sourcesmentioning

confidence: 78%

Stochastic generation of MAC waves and implications for convection in Earth’s core

Buffett

Knezek

2017

Geophysical Journal International

View full text Add to dashboard Cite

“…These are typically based on dynamics relevant to core flow, such as tangentially geostrophic (TG) flow, purely toroidal (PT) flow and helical flow [see, e.g., Holme, 2007], as well as the recent quasigeostrophic flow [Pais and Jault, 2008]. Among these the TG assumption has been most commonly employed, in which the Lorentz force is eliminated from the horizontal force balance at the core surface, resulting in TG equilibrium.…”

Section: Introductionmentioning

confidence: 99%

“…Instead of fitting the observed SV tightly, one needs to allow for a possible error from the unmodeled SV [Pais and Jault, 2008;Gillet et al, 2009]. The theoretical non-uniqueness problem in the flow modeling [e.g., Holme, 2007] is another setback which is even more serious. Assumptions used to alleviate the flow uncertainty can distort resulting flow images more significantly than the errors estimated for the unmodeled SV.…”

Section: Introductionmentioning

confidence: 99%

Radial vorticity constraint in core flow modeling

Asari

Lesur

2011

J. Geophys. Res.

View full text Add to dashboard Cite

[1] We present a new method for estimating core surface flows by relaxing the tangentially geostrophic (TG) constraint. Ageostrophic flows are allowed if they are consistent with the radial component of the vorticity equation under assumptions of the magnetostrophic force balance and an insulating mantle. We thus derive a tangentially magnetostrophic (TM) constraint for flows in the spherical harmonic domain and implement it in a least squares inversion of GRIMM-2, a recently proposed core field model, for temporally continuous core flow models (2000.0-2010.0). Comparing the flows calculated using the TG and TM constraints, we show that the number of degrees of freedom for the poloidal flows is notably increased by admitting ageostrophic flows compatible with the TM constraint. We find a significantly improved fit to the GRIMM-2 secular variation (SV) by including zonal poloidal flow in TM flow models. Correlations between the predicted and observed length-of-day variations are equally good under the TG and TM constraints. In addition, we estimate flow models by imposing the TM constraint together with other dynamical constraints: either purely toroidal (PT) flow or helical flow constraint. For the PT case we cannot find any flow which explains the observed SV, while for the helical case the SV can be fitted. The poor compatibility between the TM and PT constraints seems to arise from the absence of zonal poloidal flows. The PT flow assumption is likely to be negated when the radial magnetostrophic vorticity balance is taken into account, even if otherwise consistent with magnetic observations.

show abstract

Large-Scale Flow in the Core

Cited by 137 publications

References 82 publications

An accelerating high-latitude jet in Earth’s core

An accelerating high-latitude jet in Earth’s core

Stochastic generation of MAC waves and implications for convection in Earth’s core

Radial vorticity constraint in core flow modeling

Contact Info

Product

Resources

About