@article{RuedigerKueker2021,
  author    = {R{\"u}diger, G{\"u}nther and K{\"u}ker, Manfred},
  title     = {Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation},
  series = {Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)},
  volume    = {649},
  journal   = {Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/202039912},
  pages     = {10},
  year      = {2021},
  abstract  = {In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses and the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) B theta B phi transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport, which result from hydrodynamic calculations. Only for B theta B phi>0 (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.},
  language  = {en}
}
@article{RuedigerKuekerKaepylae2020,
  author    = {R{\"u}diger, G{\"u}nther and K{\"u}ker, Manfred and K{\"a}pyl{\"a}, Petri J.},
  title     = {Electrodynamics of turbulent fluids with fluctuating electric conductivity},
  series = {Journal of plasma physics},
  volume    = {86},
  journal   = {Journal of plasma physics},
  number    = {3},
  publisher = {Cambridge Univ. Press},
  address   = {London},
  issn      = {0022-3778},
  doi       = {10.1017/S0022377820000665},
  pages     = {14},
  year      = {2020},
  abstract  = {Consequences of fluctuating microscopic conductivity in mean-field electrodynamics of turbulent fluids are formulated and discussed. If the conductivity fluctuations are assumed to be uncorrelated with the velocity fluctuations then only the turbulence-originated magnetic diffusivity of the fluid is reduced and the decay time of a large-scale magnetic field or the cycle times of oscillating turbulent dynamo models are increased. If, however, the fluctuations of conductivity and flow in a certain well-defined direction are correlated, an additional diamagnetic pumping effect results, transporting the magnetic field in the opposite direction to the diffusivity flux vector <eta'u'>. In the presence of global rotation, even for homogeneous turbulence fields, an alpha effect appears. If the characteristic values of the outer core of the Earth or the solar convection zone are applied, the dynamo number of the new alpha effect does not reach supercritical values to operate as an alpha(2)-dynamo but oscillating alpha Omega-dynamos with differential rotation are not excluded.},
  language  = {en}
}
@article{RuedigerKuekerKapylaetal.2019,
  author    = {R{\"u}diger, G{\"u}nther and K{\"u}ker, Manfred and Kapyla, P. J. and Strassmeier, Klaus G.},
  title     = {Antisolar differential rotation of slowly rotating cool stars},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {630},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201935280},
  pages     = {9},
  year      = {2019},
  abstract  = {Rotating stellar convection transports angular momentum towards the equator, generating the characteristic equatorial acceleration of the solar rotation while the radial flux of angular momentum is always inwards. New numerical box simulations for the meridional cross-correlation < u(theta)u(phi)>, however, reveal the angular momentum transport towards the poles for slow rotation and towards the equator for fast rotation. The explanation is that for slow rotation a negative radial gradient of the angular velocity always appears, which in combination with a so-far neglected rotation-induced off-diagonal eddy viscosity term nu(perpendicular to) provides "antisolar rotation" laws with a decelerated equator Similarly, the simulations provided positive values for the rotation-induced correlation < u(r)u(theta)>, which is relevant for the resulting latitudinal temperature profiles (cool or warm poles) for slow rotation and negative values for fast rotation. Observations of the differential rotation of slowly rotating stars will therefore lead to a better understanding of the actual stress-strain relation, the heat transport, and the underlying model of the rotating convection.},
  language  = {en}
}
@phdthesis{Kueker1996,
  author    = {K{\"u}ker, Manfred},
  title     = {Theorie der differentiellen Rotation der Sonne und ihrer magnetfeldbedingten Torsionsschwingungen},
  pages     = {77 S.},
  year      = {1996},
  language  = {de}
}