Open Access
Boundary Layer Control of Rotating Convection Systems
Eric M. King,Stephan Stellmach,Jerome Noir,Ulrich Hansen,Jonathan M. Aurnou +4 more
- Vol. 2008
TLDR
This work forms a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers, and unifies the disparate results of an extensive array of previous experiments, and is broadly applicable to natural convection systems.Abstract:
Turbulent rotating convection is an important dynamical process occurring on nearly all planetary and stellar bodies, influencing many observed features such as magnetic fields, atmospheric jets and emitted heat flux patterns. For decades, it has been thought that the importance of rotation's influence on convection depends on the competition between the two relevant forces in the system: buoyancy (non-rotating) and Coriolis (rotating). The force balance argument does not, however, accurately predict the transition from rotationally controlled to non-rotating heat transfer behaviour. New results from laboratory and numerical experiments suggest that the transition is in fact controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. Turbulent rotating convection controls many observed features in stars and planets, such as magnetic fields. It has been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force. This paper presents results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. Turbulent rotating convection controls many observed features of stars and planets, such as magnetic fields, atmospheric jets and emitted heat flux patterns1,2,3,4,5,6. It has long been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force7,8,9,10,11,12. Here, however, we present results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. We formulate a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers. This transition scaling theory unifies the disparate results of an extensive array of previous experiments8,9,10,11,12,13,14,15, and is broadly applicable to natural convection systems.read more
Citations
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Journal ArticleDOI
Dynamo Scaling Laws and Applications to the Planets
TL;DR: The scaling laws for planetary dynamos relate the characteristic magnetic field strength, characteristic flow velocity and other properties to primary quantities such as core size, rotation rate, electrical conductivity and heat flux as discussed by the authors.
Journal ArticleDOI
On the genesis of the Earth's magnetism
Paul H. Roberts,Eric M. King +1 more
TL;DR: The geophysical relevance of the experiments and simulations is called into question: the dynamics of Earth's core are too complex, and operate across time and length scales too broad to be captured by any single laboratory experiment, or resolved on present-day computers.
Journal ArticleDOI
Statistical and physical balances in low Rossby number Rayleigh–Bénard convection
TL;DR: In this paper, the authors studied rapid rotating Rayleigh-benard convection using an asymptotically reduced equation set valid in the limit of low Rossby numbers and identified four distinct dynamical regimes: a disordered cellular regime near threshold, a regime of weakly interacting convective Taylor columns at larger Rayleigh numbers, followed by a breakdown of the convective columns into disordered plume regime characterized by reduced efficiency and finally by geostrophic turbulence.
Journal ArticleDOI
Heat transfer by rapidly rotating Rayleigh–Bénard convection
TL;DR: In this paper, an exact scaling law for heat transfer by geostrophic convection, by considering the stability of the thermal boundary layers, where, and are the Nusselt, Rayleigh and Ekman numbers, respectively, and is the critical Rayleigh number for the onset of convection.
Journal ArticleDOI
Rotating convective turbulence in Earth and planetary cores
Jonathan M. Aurnou,Michael A. Calkins,Jonathan S. Cheng,Keith Julien,E.M. King,David Nieves,Krista M. Soderlund,Stephan Stellmach +7 more
TL;DR: In this paper, a closely coupled suite of advanced asymptotically-reduced theoretical models, efficient Cartesian direct numerical simulations (DNS) and laboratory experiments are presented.
References
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Journal ArticleDOI
Giant impacts, core stratification, and failure of the Martian dynamo
TL;DR: In this article, the authors studied the impact-induced temperature increase in the Martian mantle and core, adopting the "ordinary" and "foundering" shock heating mechanisms proposed by Watters et al. and impact velocities of 10 and 15 km/s.
Journal ArticleDOI
Boundary layers in rotating weakly turbulent Rayleigh-Bénard convection
TL;DR: In this article, the effect of rotation on the boundary layers (BLs) in a Rayleigh-Benard system at a relatively low Rayleigh number, i.e., Ra = 4×10^7, is studied for different Pr by direct numerical simulations and the results are compared with laminar BL theory.
Journal ArticleDOI
The geostrophic regime of rapidly rotating turbulent convection
TL;DR: The rotating Rayleigh-Benard convection is a simple model system used to study the interplay of buoyant forcing and rotation as discussed by the authors, and it has been applied to the geostrophic regime of turbulent rot.
Journal ArticleDOI
Magnetic reversal frequency scaling in dynamos with thermochemical convection
Peter Olson,Hagay Amit +1 more
TL;DR: In this article, scaling relationships for the frequency of magnetic polarity reversals in numerical dynamos powered by thermochemical convection were derived, and the average number of reversals per unit unit of time scales with the local Rossby number Ro l of the convection.
Journal ArticleDOI
Thermal core-mantle coupling in an early lunar dynamo: Implications for a global magnetic field and magnetosphere of the early Moon
TL;DR: In this paper, the authors carried out numerical simulations of a possible lunar dynamo, including effects of mantle overturn on heat flux heterogeneity at the core-mantle boundary, and found that the surface field intensity of the lunar dynamos is about 100 nT.