Large-scale vortices and zonal flows in spherical rotating convection

Lin, Yufeng; Jackson, Andrew C.

doi:10.1017/jfm.2020.1151

Cited by 10 publications

(3 citation statements)

References 45 publications

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“…In the hydrodynamic run RHD5, a strong axial jet develops. Similar flow structures have recently been reported from simulations of Boussinesq convection in rotating full spheres (Lin & Jackson 2021). This feature is not present in the corresponding MHD run MHD5 (see Fig.…”

Section: Description Of Convective Statessupporting

confidence: 86%

Star-in-a-box simulations of fully convective stars

Käpylä

2021

A&A

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Context. Main-sequence late-type stars with masses of less than 0.35 M⊙ are fully convective. Aims. The goal is to study convection, differential rotation, and dynamos as functions of rotation in fully convective stars. Methods. Three-dimensional hydrodynamic and magnetohydrodynamic numerical simulations with a star-in-a-box model, in which a spherical star is immersed inside of a Cartesian cube, are used. The model corresponds to a 0.2 M⊙ main-sequence M5 dwarf. A range of rotation periods (Prot) between 4.3 and 430 d is explored. Results. The slowly rotating model with Prot = 430 days produces anti-solar differential rotation with a slow equator and fast poles, along with predominantly axisymmetric quasi-steady large-scale magnetic fields. For intermediate rotation (Prot = 144 and 43 days) the differential rotation is solar-like (fast equator, slow poles), and the large-scale magnetic fields are mostly axisymmetric and either quasi-stationary or cyclic. The latter occurs in a similar parameter regime as in other numerical studies in spherical shells, and the cycle period is similar to observed cycles in fully convective stars with rotation periods of roughly 100 days. In the rapid rotation regime the differential rotation is weak and the large-scale magnetic fields are increasingly non-axisymmetric with a dominating m = 1 mode. This large-scale non-axisymmetric field also exhibits azimuthal dynamo waves. Conclusions. The results of the star-in-a-box models agree with simulations of partially convective late-type stars in spherical shells in that the transitions in differential rotation and dynamo regimes occur at similar rotational regimes in terms of the Coriolis (inverse Rossby) number. This similarity between partially and fully convective stars suggests that the processes generating differential rotation and large-scale magnetism are insensitive to the geometry of the star.

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Section: Description Of Convective Statessupporting

confidence: 86%

Star-in-a-box simulations of fully convective stars

Käpylä

2021

A&A

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“…For a fixed value of , the number of jets is controlled both by the Rayleigh number and the shell aspect ratio, . In full sphere and small aspect ratio geometries (), simulations typically find a single prograde jet in the equatorial region and retrograde jets at higher latitudes (Aurnou & Olson 2001; Christensen 2002; Lin & Jackson 2021). As and are increased, there is a tendency for multiple jets to form at higher latitudes, leading to a banded structure that is reminiscent of the flows observed on the gas giant planets (Christensen 2001; Heimpel, Aurnou & Wicht 2005; Jones & Kuzanyan 2009; Gastine, Heimpel & Wicht 2014; Heimpel et al.…”

Section: Introductionmentioning

confidence: 99%

“…Later investigations have found that this loss of correlation in the small-scale velocity is a monotonically decreasing function of (Showman, Kaspi & Flierl 2011; Gastine & Wicht 2012). For sufficiently large Rayleigh numbers, Christensen (2002) and Lin & Jackson (2021) find evidence that the zonal flow scaling approaches a ‘diffusion-free’ regime, so-called because of the lack of dependence on and , though within this regime, the dynamics is no longer geostrophic since inertia and the Coriolis force are of the same order of magnitude.…”

Section: Introductionmentioning

confidence: 99%

Asymptotic scaling relations for rotating spherical convection with strong zonal flows

Nicoski,

O'Connor,

Calkins

2024

J. Fluid Mech.

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We analyse the results of direct numerical simulations of rotating convection in spherical shell geometries with stress-free boundary conditions, which develop strong zonal flows. Both the Ekman number and the Rayleigh number are varied. We find that the asymptotic theory for rapidly rotating convection can be used to predict the Ekman number dependence of each term in the governing equations, along with the convective flow speeds and the dominant length scales. Using a balance between the Reynolds stress and the viscous stress, together with the asymptotic scaling for the convective velocity, we derive an asymptotic prediction for the scaling behaviour of the zonal flow with respect to the Ekman number, which is supported by the numerical simulations. We do not find evidence of distinct asymptotic scalings for the buoyancy and viscous forces and, in agreement with previous results from asymptotic plane layer models, we find that the ratio of the viscous force to the buoyancy force increases with Rayleigh number. Thus, viscosity remains non-negligible and we do not observe a trend towards a diffusion-free scaling behaviour within the rapidly rotating regime.

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