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Publikasjoner (10 av 53) Visa alla publikasjoner
Rogachevskii, I. & Kleeorin, N. (2024). Semi-organized structures and turbulence in the atmospheric convection. Physics of fluids, 36(2), Article ID 026610.
Åpne denne publikasjonen i ny fane eller vindu >>Semi-organized structures and turbulence in the atmospheric convection
2024 (engelsk)Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, nr 2, artikkel-id 026610Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The atmospheric convective boundary layer (CBL) consists of three basic parts: (1) the surface layer unstably stratified and dominated by small-scale turbulence of very complex nature; (2) the CBL core dominated by the energy-, momentum-, and mass-transport of semi-organized structures (large-scale circulations), with a small contribution from small-scale turbulence produced by local structural shears; and (3) turbulent entrainment layer at the upper boundary, characterized by essentially stable stratification with negative (downward) turbulent flux of potential temperature. The energy- and flux budget theory developed previously for atmospheric stably-stratified turbulence and the surface layer in atmospheric convective turbulence is extended to the CBL core using budget equations for turbulent energies and turbulent fluxes of buoyancy and momentum. For the CBL core, we determine global turbulent characteristics (averaged over the entire volume of the semi-organized structure) as well as kinetic and thermal energies of the semi-organized structures as the functions of the aspect ratio of the semi-organized structure, the scale separation parameter between the vertical size of the structures and the integral scale of turbulence and the degree of thermal anisotropy characterized the form of plumes. The obtained theoretical relationships are potentially useful in modeling applications in the atmospheric convective boundary-layer and analysis of laboratory and field experiments, direct numerical simulations, and large-eddy simulations of convective turbulence with large-scale semi-organized structures.

HSV kategori
Identifikatorer
urn:nbn:se:su:diva-227433 (URN)10.1063/5.0188732 (DOI)001162437700001 ()2-s2.0-85185003056 (Scopus ID)
Tilgjengelig fra: 2024-03-13 Laget: 2024-03-13 Sist oppdatert: 2024-03-13bibliografisk kontrollert
Brandenburg, A., Rogachevskii, I. & Schober, J. (2023). Dissipative magnetic structures and scales in small-scale dynamos. Monthly notices of the Royal Astronomical Society, 518(4), 6367-6375
Åpne denne publikasjonen i ny fane eller vindu >>Dissipative magnetic structures and scales in small-scale dynamos
2023 (engelsk)Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 518, nr 4, s. 6367-6375Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Small-scale dynamos play important roles in modern astrophysics, especially on galactic and extragalactic scales. Owing to dynamo action, purely hydrodynamic Kolmogorov turbulence hardly exists and is often replaced by hydromagnetic turbulence. Understanding the size of dissipative magnetic structures is important in estimating the time-scale of galactic scintillation and other observational and theoretical aspects of interstellar and intergalactic small-scale dynamos. Here we show that, during the kinematic phase of the small-scale dynamo, the cutoff wavenumber of the magnetic energy spectra scales as expected for large magnetic Prandtl numbers, but continues in the same way also for moderately small values – contrary to what is expected. For a critical magnetic Prandtl number of about 0.3, the dissipative and resistive cutoffs are found to occur at the same wavenumber. In the non-linearly saturated regime, the critical magnetic Prandtl number becomes unity. The cutoff scale now has a shallower scaling with magnetic Prandtl number below a value of about three, and a steeper one otherwise compared to the kinematic regime.

Emneord
dynamo, MHD, turbulence, galaxies: magnetic fields
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-214545 (URN)10.1093/mnras/stac3555 (DOI)000904583300009 ()
Tilgjengelig fra: 2023-02-10 Laget: 2023-02-10 Sist oppdatert: 2023-02-10bibliografisk kontrollert
Kleeorin, N., Rogachevskii, I., Safiullin, N., Gershberg, R. & Porshnev, S. (2023). Magnetic fields of low-mass main sequences stars: non-linear dynamo theory and mean-field numerical simulations. Monthly notices of the Royal Astronomical Society, 526(2), 1601-1612
Åpne denne publikasjonen i ny fane eller vindu >>Magnetic fields of low-mass main sequences stars: non-linear dynamo theory and mean-field numerical simulations
Vise andre…
2023 (engelsk)Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 526, nr 2, s. 1601-1612Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Our theoretical and numerical analysis have suggested that for low-mass main sequences stars (of the spectral classes from M5 to G0) rotating much faster than the Sun, the generated large-scale magnetic field is caused by the mean-field alpha(2)Omega dynamo, whereby the alpha(2) dynamo is modified by a weak differential rotation. Even for a weak differential rotation, the behaviour of the magnetic activity is changed drastically from aperiodic regime to non-linear oscillations and appearance of a chaotic behaviour with increase of the differential rotation. Periods of the magnetic cycles decrease with increase of the differential rotation, and they vary from tens to thousand years. This long-term behaviour of the magnetic cycles may be related to the characteristic time of the evolution of the magnetic helicity density of the small-scale field. The performed analysis is based on the mean-field simulations (MFS) of the alpha(2)Omega and alpha(2) dynamos and a developed non-linear theory of alpha(2) dynamo. The applied MFS model was calibrated using turbulent parameters typical for the solar convective zone.

Emneord
dynamo, MHD, turbulence, stars: low-mass, stars: magnetic fields
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-223767 (URN)10.1093/mnras/stad2708 (DOI)001078226700001 ()2-s2.0-85174534990 (Scopus ID)
Tilgjengelig fra: 2023-11-15 Laget: 2023-11-15 Sist oppdatert: 2023-11-15bibliografisk kontrollert
Schober, J., Rogachevskii, I. & Brandenburg, A. (2022). Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential. Physical Review D: covering particles, fields, gravitation, and cosmology, 105(4), Article ID 043507.
Åpne denne publikasjonen i ny fane eller vindu >>Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential
2022 (engelsk)Inngår i: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 105, nr 4, artikkel-id 043507Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We study the dynamics of magnetic fields in chiral magnetohydrodynamics, which takes into account the effects of an additional electric current related to the chiral magnetic effect in high-energy plasmas. We perform direct numerical simulations, considering weak seed magnetic fields and inhomogeneities of the chiral chemical potential μ5 with a zero mean. We demonstrate that a small-scale chiral dynamo can occur in such plasmas if fluctuations of μ5 are correlated on length scales that are much larger than the scale on which the dynamo growth rate reaches its maximum. Magnetic fluctuations grow by many orders of magnitude due to the small-scale chiral dynamo instability. Once the nonlinear backreaction of the generated magnetic field on fluctuations of μ5 sets in, the ratio of these scales decreases and the dynamo saturates. When magnetic fluctuations grow sufficiently to drive turbulence via the Lorentz force before reaching maximum field strength, an additional mean-field dynamo phase is identified. The mean magnetic field grows on a scale that is larger than the integral scale of turbulence after the amplification of the fluctuating component saturates. The growth rate of the mean magnetic field is caused by a magnetic α effect that is proportional to the current helicity. With the onset of turbulence, the power spectrum of μ5 develops a universal k−1 scaling independently of its initial shape, while the magnetic energy spectrum approaches a k−3 scaling.

HSV kategori
Identifikatorer
urn:nbn:se:su:diva-202870 (URN)10.1103/PhysRevD.105.043507 (DOI)000754626800007 ()
Tilgjengelig fra: 2022-03-21 Laget: 2022-03-21 Sist oppdatert: 2022-03-21bibliografisk kontrollert
Rogachevskii, I., Kleeorin, N. & Zilitinkevich, S. (2022). Energy- and flux-budget theory for surface layers in atmospheric convective turbulence. Physics of fluids, 34(11), Article ID 116602.
Åpne denne publikasjonen i ny fane eller vindu >>Energy- and flux-budget theory for surface layers in atmospheric convective turbulence
2022 (engelsk)Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 34, nr 11, artikkel-id 116602Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The energy- and flux-budget (EFB) theory developed previously for atmospheric stably stratified turbulence is extended to the surface layer in atmospheric convective turbulence. This theory is based on budget equations for turbulent energies and fluxes in the Boussinesq approximation. In the lower part of the surface layer in the atmospheric convective boundary layer, the rate of turbulence production of the turbulent kinetic energy (TKE) caused by the surface shear is much larger than that caused by the buoyancy, which results in three-dimensional turbulence of very complex nature. In the upper part of the surface layer, the rate of turbulence production of TKE due to the shear is much smaller than that caused by the buoyancy, which causes unusual strongly anisotropic buoyancy-driven turbulence. Considering the applications of the obtained results to the atmospheric convective boundary-layer turbulence, the theoretical relationships potentially useful in modeling applications have been derived. The developed EFB theory allows us to obtain a smooth transition between a stably stratified turbulence to a convective turbulence. The EFB theory for the surface layer in a convective turbulence provides an analytical expression for the entire surface layer including the transition range between the lower and upper parts of the surface layer, and it allows us to determine the vertical profiles for all turbulent characteristics, including TKE, the intensity of turbulent potential temperature fluctuations, the vertical turbulent fluxes of momentum and buoyancy (proportional to potential temperature), the integral turbulence scale, the turbulence anisotropy, the turbulent Prandtl number, and the flux Richardson number. 

HSV kategori
Identifikatorer
urn:nbn:se:su:diva-212446 (URN)10.1063/5.0123401 (DOI)000880665300007 ()
Tilgjengelig fra: 2022-12-12 Laget: 2022-12-12 Sist oppdatert: 2022-12-12bibliografisk kontrollert
Schober, J., Rogachevskii, I. & Brandenburg, A. (2022). Production of a Chiral Magnetic Anomaly with Emerging Turbulence and Mean-Field Dynamo Action. Physical Review Letters, 128(6), Article ID 065002.
Åpne denne publikasjonen i ny fane eller vindu >>Production of a Chiral Magnetic Anomaly with Emerging Turbulence and Mean-Field Dynamo Action
2022 (engelsk)Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 128, nr 6, artikkel-id 065002Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In relativistic magnetized plasmas, asymmetry in the number densities of left- and right-handed fermions, i.e., a nonzero chiral chemical potential μ5, leads to an electric current along the magnetic field. This causes a chiral dynamo instability for a uniform μ5, but our simulations reveal a dynamo even for fluctuating μ5 with zero mean. It produces magnetically dominated turbulence and generates mean magnetic fields via the magnetic α effect. Eventually, a universal scale-invariant k−1 spectrum of μ5 and a k−3 magnetic spectrum are formed independently of the initial condition.

HSV kategori
Identifikatorer
urn:nbn:se:su:diva-202755 (URN)10.1103/PhysRevLett.128.065002 (DOI)000754677600006 ()35213203 (PubMedID)
Tilgjengelig fra: 2022-03-11 Laget: 2022-03-11 Sist oppdatert: 2022-03-11bibliografisk kontrollert
Kleeorin, N. & Rogachevskii, I. (2022). Turbulent magnetic helicity fluxes in solar convective zone. Monthly notices of the Royal Astronomical Society, 515(4), 5437-5448
Åpne denne publikasjonen i ny fane eller vindu >>Turbulent magnetic helicity fluxes in solar convective zone
2022 (engelsk)Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 515, nr 4, s. 5437-5448Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Combined action of helical motions of plasma (the kinetic alpha effect) and non-uniform (differential) rotation is a key dynamo mechanism of solar and galactic large-scale magnetic fields. Dynamics of magnetic helicity of small-scale fields is a crucial mechanism in a non-linear dynamo saturation where turbulent magnetic helicity fluxes allow to avoid catastrophic quenching of the alpha effect. The convective zone of the Sun and solar-like stars, as well as galactic discs, are the source for production of turbulent magnetic helicity fluxes. In the framework of the mean-field approach and the spectral tau approximation, we derive turbulent magnetic helicity fluxes using the Coulomb gauge in a density-stratified turbulence. The turbulent magnetic helicity fluxes include non-gradient and gradient contributions. The non-gradient magnetic helicity flux is proportional to a non-linear effective velocity (which vanishes in the absence of the density stratification) multiplied by small-scale magnetic helicity, while the gradient contributions describe turbulent magnetic diffusion of the small-scale magnetic helicity. In addition, the turbulent magnetic helicity fluxes contain source terms proportional to the kinetic alpha effect or its gradients, and also contributions caused by the large-scale shear (solar differential rotation). We have demonstrated that the turbulent magnetic helicity fluxes due to the kinetic alpha effect and its radial derivative in combination with the non-linear magnetic diffusion of the small-scale magnetic helicity are dominant in the solar convective zone.

Emneord
MHD, Sun: dynamo, Sun: interior, Sun: magnetic fields, turbulence
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-209350 (URN)10.1093/mnras/stac2141 (DOI)000841942900013 ()
Tilgjengelig fra: 2022-09-16 Laget: 2022-09-16 Sist oppdatert: 2022-09-16bibliografisk kontrollert
Rogachevskii, I. & Kleeorin, N. (2021). Compressibility effects in turbulent transport of the temperature field. Physical review. E, 103(1), Article ID 013107.
Åpne denne publikasjonen i ny fane eller vindu >>Compressibility effects in turbulent transport of the temperature field
2021 (engelsk)Inngår i: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 103, nr 1, artikkel-id 013107Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Compressibility effects in a turbulent transport of temperature field are investigated by applying the quasilinear approach for small Péclet numbers and the spectral τ approach for large Péclet numbers. The compressibility of a fluid flow reduces the turbulent diffusivity of the mean temperature field similarly to that for the particle number density and magnetic field. However, expressions for the turbulent diffusion coefficient for the mean temperature field in a compressible turbulence are different from those for the mean particle number density and the mean magnetic field. The combined effect of compressibility and inhomogeneity of turbulence causes an increase of the mean temperature in the regions with more intense velocity fluctuations due to a turbulent pumping. Formally, this effect is similar to a phenomenon of compressible turbophoresis found previously [J. Plasma Phys. 84, 735840502 (2018)] for noninertial particles or gaseous admixtures. The gradient of the mean fluid pressure results in an additional turbulent pumping of the mean temperature field. The latter effect is similar to the turbulent barodiffusion of particles and gaseous admixtures. The compressibility of a fluid flow also causes a turbulent cooling of the surrounding fluid due to an additional sink term in the equation for the mean temperature field. There is no analog of this effect for particles.

HSV kategori
Identifikatorer
urn:nbn:se:su:diva-191696 (URN)10.1103/PhysRevE.103.013107 (DOI)000608619900019 ()33601522 (PubMedID)
Tilgjengelig fra: 2021-03-31 Laget: 2021-03-31 Sist oppdatert: 2022-02-25bibliografisk kontrollert
Kleeorin, N., Rogachevskii, I. & Zilitinkevich, S. (2021). Energy and flux budget closure theory for passive scalar in stably stratified turbulence. Physics of fluids, 33(7), Article ID 076601.
Åpne denne publikasjonen i ny fane eller vindu >>Energy and flux budget closure theory for passive scalar in stably stratified turbulence
2021 (engelsk)Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, nr 7, artikkel-id 076601Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The energy and flux budget (EFB) closure theory for a passive scalar (non-buoyant and non-inertial particles or gaseous admixtures) is developed for stably stratified turbulence. The physical background of the EFB turbulence closures is based on the budget equations for the turbulent kinetic and potential energies and turbulent fluxes of momentum and buoyancy as well as the turbulent flux of particles. The EFB turbulence closure is designed for stratified geophysical flows from neutral to very stable stratification, and it implies that turbulence is maintained by the velocity shear at any stratification. In a steady-state, expressions for the turbulent flux of the passive scalar and the anisotropic non-symmetric turbulent diffusion tensor are derived, and universal flux Richardson number dependencies of the components of this tensor are obtained. The diagonal component in the vertical direction of the turbulent diffusion tensor is suppressed by strong stratification, while the diagonal components in the horizontal directions are not suppressed, but they are dominant in comparison with the other components of the turbulent diffusion tensor. This implies that any initially created strongly inhomogeneous particle cloud is evolved into a thin pancake in a horizontal plane with very slow increase in its thickness in the vertical direction. The turbulent Schmidt number (the ratio of the eddy viscosity and the vertical turbulent diffusivity of the passive scalar) linearly increases with the gradient Richardson number. The physics of such a behavior is related to the buoyancy force that causes a correlation between fluctuations of the potential temperature and the particle number density. This correlation that is proportional to the product of the vertical turbulent particle flux and the vertical gradient of the mean potential temperature reduces the vertical turbulent particle flux. Considering the applications of these results to the atmospheric boundary-layer turbulence, the theoretical relationships are derived, which allows us to determine the turbulent diffusion tensor as a function of the vertical coordinate measured in the units of the local Obukhov length scale. The obtained relations are potentially useful in modeling applications of particle dispersion in the atmospheric boundary-layer turbulence and free atmosphere turbulence.

Emneord
Atmospheric dynamics, Turbulence theory and modelling, Turbulent flows, Energy flux
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-197713 (URN)10.1063/5.0052786 (DOI)000691870700001 ()
Tilgjengelig fra: 2021-10-13 Laget: 2021-10-13 Sist oppdatert: 2022-02-25bibliografisk kontrollert
Rogachevskii, I. & Kleeorin, N. (2021). Turbulent transport of radiation in the solar convective zone. Monthly notices of the Royal Astronomical Society, 508(1), 1296-1304
Åpne denne publikasjonen i ny fane eller vindu >>Turbulent transport of radiation in the solar convective zone
2021 (engelsk)Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 508, nr 1, s. 1296-1304Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A turbulent transport of radiation in the solar convective zone is investigated. The mean-field equation for the irradiation intensity is derived. It is shown that due to the turbulent effects, the effective penetration length of radiation can be increased several times in comparison with the mean penetration length of radiation (defined as an inverse mean absorption coefficient). Using the model of the solar convective zone based on mixing length theory, where the mean penetration length of radiation is usually much smaller than the turbulent correlation length, it is demonstrated that the ratio of the effective penetration length to the mean penetration length of radiation increases 2.5 times in the vicinity of the solar surface. The main reasons for this are the compressibility effects that become important in the vicinity of the solar surface where temperature and density fluctuations increase towards the solar surface, enhancing fluctuations of the radiation absorption coefficient and increasing the effective penetration length of radiation.

Emneord
radiative transfer, turbulence, Sun: interior
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-202018 (URN)10.1093/mnras/stab2595 (DOI)000741285400054 ()
Tilgjengelig fra: 2022-02-11 Laget: 2022-02-11 Sist oppdatert: 2022-02-11bibliografisk kontrollert
Organisasjoner
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-7308-4768