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Kleeorin, Nathan
Publications (8 of 8) Show all publications
Schober, J., Brandenburg, A., Rogachevskii, l. & Kleeorin, N. (2019). Energetics of turbulence generated by chiral MHD dynamos. Geophysical and Astrophysical Fluid Dynamics, 113(1-2), 107-130
Open this publication in new window or tab >>Energetics of turbulence generated by chiral MHD dynamos
2019 (English)In: Geophysical and Astrophysical Fluid Dynamics, ISSN 0309-1929, E-ISSN 1029-0419, Vol. 113, no 1-2, p. 107-130Article in journal (Refereed) Published
Abstract [en]

An asymmetry in the number density of left- and right-handed fermions is known to give rise to a new term in the induction equation that can result in a dynamo instability. At high temperatures, when a chiral asymmetry can survive for long enough, this chiral dynamo instability can amplify magnetic fields efficiently, which in turn drive turbulence via the Lorentz force. While it has been demonstrated in numerical simulations that this chiral magnetically driven turbulence exists and strongly affects the dynamics of the magnetic field, the details of this process remain unclear. The goal of this paper is to analyse the energetics of chiral magnetically driven turbulence and its effect on the generation and dynamics of the magnetic field using direct numerical simulations. We study these effects for different initial conditions, including a variation of the initial chiral chemical potential and the magnetic Prandtl number, . In particular, we determine the ratio of kinetic to magnetic energy, , in chiral magnetically driven turbulence. Within the parameter space explored in this study, reaches a value of approximately 0.064-0.074-independently of the initial chiral asymmetry and for . Our simulations suggest, that decreases as a power law when increasing by decreasing the viscosity. While the exact scaling depends on the details of the fitting criteria and the Reynolds number regime, an approximate result of is reported. Using the findings from our numerical simulations, we analyse the energetics of chiral magnetically driven turbulence in the early Universe.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2019
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-252995 (URN)10.1080/03091929.2018.1515313 (DOI)000468550900006 ()2-s2.0-85053381281 (Scopus ID)
Note

QC 20190619

Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-19Bibliographically approved
Kleeorin, N., Rogachevskii, l., Soustova, I. A., Troitskaya, Y. I., Ermakova, O. S. & Zilitinkevich, S. (2019). Internal gravity waves in the energy and flux budget turbulence-closure theory for shear-free stably stratified flows. Physical review. E, 99(6), Article ID 063106.
Open this publication in new window or tab >>Internal gravity waves in the energy and flux budget turbulence-closure theory for shear-free stably stratified flows
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2019 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063106Article in journal (Refereed) Published
Abstract [en]

We have advanced the energy and flux budget turbulence closure theory that takes into account a two-way coupling between internal gravity waves (IGWs) and the shear-free stably stratified turbulence. This theory is based on the budget equation for the total (kinetic plus potential) energy of IGWs, the budget equations for the kinetic and potential energies of fluid turbulence, and turbulent fluxes of potential temperature for waves and fluid flow. The waves emitted at a certain level propagate upward, and the losses of wave energy cause the production of turbulence energy. We demonstrate that due to the nonlinear effects more intensive waves produce more strong turbulence, and this, in turn, results in strong damping of IGWs. As a result, the penetration length of more intensive waves is shorter than that of less intensive IGWs. The anisotropy of the turbulence produced by less intensive IGWs is stronger than that caused by more intensive waves. The low-amplitude IGWs produce turbulence consisting up to 90% of turbulent potential energy. This resembles the properties of the observed high-altitude tropospheric strongly anisotropic (nearly two-dimensional) turbulence.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-255318 (URN)10.1103/PhysRevE.99.063106 (DOI)000473029000006 ()2-s2.0-85068255962 (Scopus ID)
Note

QC 20190807

Available from: 2019-08-07 Created: 2019-08-07 Last updated: 2019-08-07Bibliographically approved
Kuzanyan, K. M., Safiullin, N., Kleeorin, N., Rogachevskii, I. & Porshnev, S. (2019). Large-Scale Properties of the Tilt of Sunspot Groups and Joy's Law Near the Solar Equator. ASTROPHYSICS, 62(2), 261-275
Open this publication in new window or tab >>Large-Scale Properties of the Tilt of Sunspot Groups and Joy's Law Near the Solar Equator
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2019 (English)In: ASTROPHYSICS, Vol. 62, no 2, p. 261-275Article in journal (Refereed) Published
Abstract [en]

A physical mechanism is proposed for the formation of the tilt angle of groups of sunspots during the formation of active regions under the sun's photosphere. The phenomena associated with the influence of Coriolis forces on the large-scale flows in supergranular convection in turbulent media are studied in detail. Based on calculations of the magnetic field in a model of a solar nonlinear dynamo, the orders of magnitude of this effect are estimated and the tilt angle is estimated in the band of latitudes in the royal zone of sunspot activity. This dynamo model is based on the balance of small- and large-scale magnetic helicities, and describes the formation of sunspots over the last five activity cycles (since 1964) and has been adapted for a broader class of magnetic manifestations of solar activity. The variation in the average tilt over these five activity cycles has been plotted and latitude-time diagrams of the distribution of this value constructed which fully satisfy Joy's law and also show the local deviations from it within a limited range of latitudes in isolated phases of the solar cycle.

Place, publisher, year, edition, pages
SPRINGER/PLENUM PUBLISHERS, 2019
Keywords
sunspots, solar cycle, solar dynamo, turbulence
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-252588 (URN)10.1007/s10511-019-09579-2 (DOI)000468031100010 ()2-s2.0-85065990078 (Scopus ID)
Note

QC 20190611

Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-06-11Bibliographically approved
Losada, I., Warnecke, J., Brandenburg, A., Kleeorin, N. & Rogachevskii, l. (2019). Magnetic bipoles in rotating turbulence with coronal envelope. Astronomy and Astrophysics, 621, Article ID A61.
Open this publication in new window or tab >>Magnetic bipoles in rotating turbulence with coronal envelope
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A61Article in journal (Refereed) Published
Abstract [en]

Context. The formation mechanism of sunspots and starspots is not yet fully understood. It is a major open problem in astrophysics. Aims. Magnetic flux concentrations can be produced by the negative effective magnetic pressure instability (NEMPI). This instability is strongly suppressed by rotation. However, the presence of an outer coronal envelope was previously found to strengthen the flux concentrations and make them more prominent. It also allows for the formation of bipolar regions (BRs). We aim to understand the important issue of whether the presence of an outer coronal envelope also changes the excitation conditions and the rotational dependence of NEMPI. Methods. We have used direct numerical simulations and mean-field simulations. We adopted a simple two-layer model of turbulence that mimics the jump between the convective turbulent and coronal layers below and above the surface of a star, respectively. The computational domain is Cartesian and located at a certain latitude of a rotating sphere. We investigated the effects of rotation on NEMPI by changing the Coriolis number, the latitude, the strengths of the imposed magnetic field, and the box resolution. Results. Rotation has a strong impact on the process of BR formation. Even rather slow rotation is found to suppress BR formation. However, increasing the imposed magnetic field strength also makes the structures stronger and alleviates the rotational suppression somewhat. The presence of a coronal layer itself does not significantly reduce the effects of rotational suppression.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
magnetohydrodynamics (MHD), turbulence, dynamo, Sun: magnetic fields, Sun: rotation, Sun: activity
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-241309 (URN)10.1051/0004-6361/201833018 (DOI)000455172300001 ()2-s2.0-85059893132 (Scopus ID)
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved
Rogachevskii, I., Kleeorin, N. & Brandenburg, A. (2018). Compressibility in turbulent magnetohydrodynamics and passive scalar transport: mean-field theory. Journal of Plasma Physics, 84(5), Article ID 735840502.
Open this publication in new window or tab >>Compressibility in turbulent magnetohydrodynamics and passive scalar transport: mean-field theory
2018 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 5, article id 735840502Article in journal (Refereed) Published
Abstract [en]

We develop a mean-field theory of compressibility effects in turbulent magnetohydrodynamics and passive scalar transport using the quasi-linear approximation and the spectral tau-approach. We find that compressibility decreases the a effect and the turbulent magnetic diffusivity both at small and large magnetic Reynolds numbers, Rm. Similarly, compressibility decreases the turbulent diffusivity for passive scalars both at small and large Peclet numbers, Pe. On the other hand, compressibility does not affect the effective pumping velocity of the magnetic field for large Rm, but it decreases it for small Rm. Density stratification causes turbulent pumping of passive scalars, but it is found to become weaker with increasing compressibility. No such pumping effect exists for magnetic fields. However, compressibility results in a new passive scalar pumping effect from regions of low to high turbulent intensity both for small and large Peclet numbers. It can be interpreted as compressible turbophoresis of non-inertial particles and gaseous admixtures, while the classical turbophoresis effect exists only for inertial particles and causes them to be pumped to regions with lower turbulent intensity.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
astrophysical plasmas, plasma nonlinear phenomena
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-240025 (URN)10.1017/S0022377818000983 (DOI)000450961400001 ()
Note

QC 20181210

Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2018-12-10Bibliographically approved
Kleeorin, N. & Rogachevskii, l. (2018). Generation of large-scale vorticity in rotating stratified turbulence with inhomogeneous helicity: mean-field theory. Journal of Plasma Physics, 84(3), Article ID 735840303.
Open this publication in new window or tab >>Generation of large-scale vorticity in rotating stratified turbulence with inhomogeneous helicity: mean-field theory
2018 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 3, article id 735840303Article in journal (Refereed) Published
Abstract [en]

We discuss a mean-field theory of the generation of large-scale vorticity in a rotating density stratified developed turbulence with inhomogeneous kinetic helicity. We show that the large-scale non-uniform flow is produced due to either a combined action of a density stratified rotating turbulence and uniform kinetic helicity or a combined effect of a rotating incompressible turbulence and inhomogeneous kinetic helicity. These effects result in the formation of a large-scale shear, and in turn its interaction with the small-scale turbulence causes an excitation of the large-scale instability (known as a vorticity dynamo) due to a combined effect of the large-scale shear and Reynolds stress-induced generation of the mean vorticity. The latter is due to the effect of large-scale shear on the Reynolds stress. A fast rotation suppresses this large-scale instability.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
astrophysical plasmas, plasma nonlinear phenomena
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-231723 (URN)10.1017/S0022377818000417 (DOI)000435235200007 ()
Note

QC 20180814

Available from: 2018-08-14 Created: 2018-08-14 Last updated: 2018-08-14Bibliographically approved
Schober, J., Rogachevskii, I., Brandenburg, A., Boyarsky, A., Fröhlich, J., Ruchayskiy, O. & Kleeorin, N. (2018). Laminar and Turbulent Dynamos in Chiral Magnetohydrodynamics. II. Simulations. Astrophysical Journal, 858(2), Article ID 124.
Open this publication in new window or tab >>Laminar and Turbulent Dynamos in Chiral Magnetohydrodynamics. II. Simulations
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2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 858, no 2, article id 124Article in journal (Refereed) Published
Abstract [en]

Using direct numerical simulations (DNS), we study laminar and turbulent dynamos in chiral magnetohydrodynamics with an extended set of equations that accounts for an additional contribution to the electric current due to the chiral magnetic effect (CME). This quantum phenomenon originates from an asymmetry between left-and right-handed relativistic fermions in the presence of a magnetic field and gives rise to a chiral dynamo. We show that the magnetic field evolution proceeds in three stages: (1) a small-scale chiral dynamo instability, (2) production of chiral magnetically driven turbulence and excitation of a large-scale dynamo instability due to a new chiral effect (alpha(mu) effect), and (3) saturation of magnetic helicity and magnetic field growth controlled by a conservation law for the total chirality. The alpha(mu) effect becomes dominant at large fluid and magnetic Reynolds numbers and is not related to kinetic helicity. The growth rate of the large-scale magnetic field and its characteristic scale measured in the numerical simulations agree well with theoretical predictions based on mean-field theory. The previously discussed two-stage chiral magnetic scenario did not include stage (2), during which the characteristic scale of magnetic field variations can increase by many orders of magnitude. Based on the findings from numerical simulations, the relevance of the CME and the chiral effects revealed in the relativistic plasma of the early universe and of protoneutron stars are discussed.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018
Keywords
early universe, magnetic fields, magnetohydrodynamics (MHD), relativistic processes, stars: neutron, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-230523 (URN)10.3847/1538-4357/aaba75 (DOI)000433065500011 ()2-s2.0-85047427531 (Scopus ID)
Funder
Swedish Research CouncilEU, Horizon 2020, 665667
Note

QC 20180724

Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-07-24Bibliographically approved
Rogachevskii, I. & Kleeorin, N. (2018). Mean-field theory of differential rotation in density stratified turbulent convection. Journal of Plasma Physics, 84(2), Article ID 735840201.
Open this publication in new window or tab >>Mean-field theory of differential rotation in density stratified turbulent convection
2018 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 2, article id 735840201Article in journal (Refereed) Published
Abstract [en]

A mean-field theory of differential rotation in a density stratified turbulent convection has been developed. This theory is based on the combined effects of the turbulent heat flux and anisotropy of turbulent convection on the Reynolds stress. A coupled system of dynamical budget equations consisting in the equations for the Reynolds stress, the entropy fluctuations and the turbulent heat flux has been solved. To close the system of these equations, the spectral tau approach, which is valid for large Reynolds and Peclet numbers, has been applied. The adopted model of the background turbulent convection takes into account an increase of the turbulence anisotropy and a decrease of the turbulent correlation time with the rotation rate. This theory yields the radial profile of the differential rotation which is in agreement with that for the solar differential rotation.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
astrophysical plasmas, plasma nonlinear phenomena
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-228280 (URN)10.1017/S0022377818000272 (DOI)000431140300005 ()2-s2.0-85069160479 (Scopus ID)
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2019-10-04Bibliographically approved
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