Recent research highlights

      

Large-scale fields from shear-flow turbulence

  • compatible with incoherent alpha-shear dynamo
  • shear-current dynamo not excited
  • shown with test-field method
  • all components of diffusion tensor obtained
  •              

    Brandenburg, A., Rädler, K.-H., Rheinhardt, M., & Käpylä, P. J.: 2008, ``Magnetic diffusivity tensor and dynamo effects in rotating and shearing turbulence,'' Astrophys. J. 676, 740-751 (arXiv:0710.4059, ADS, PDF)

    citations
    125 on ADS,
    137 on Google Scholar

          

    Kinematic alpha effect in isotropic turbulence simulations

  • test-field method applied to isotropic turbulence
  • shows that turb. diffusion ηt=⅓τu2rms.
  • and τ=(urmskf)-1 to good approximation
  •              

    Sur, S., Brandenburg, A., & Subramanian, K.: 2008, ``Kinematic alpha effect in isotropic turbulence simulations,'' Monthly Notices Roy. Astron. Soc. 385, L15-L19 (arXiv:0711.3789, ADS, PDF)

    citations
    90 on ADS,
    96 on Google Scholar

          

    Large-scale dynamos in turbulent convection with shear

  • α-Ω type dynamos from convection
  • Strong horizontally averaged fields
  • Horizontal shear: drives magnetic helicity vertically
  • Vertical shear: drives magnetic helicity horizontally
  • Quenching alleviated by normal-field condition
  •              

    Käpylä, P. J., Korpi, M. J., & Brandenburg, A.: 2008, ``Large-scale dynamos in turbulent convection with shear,'' Astron. Astrophys. 491, 353-362 (arXiv:0806.0375, ADS, PDF)

    citations
    107 on ADS,
    120 on Google Scholar

          

    Cyclic magnetic activity due to turbulent convection in spherical wedge geometry

  • Convectively driven dynamo in spherical wedge
  • produces long cycle periods (∼33 years)
  • equatorward migration of toroidal flux belts
  • Hossenfelder's blog entry about the Sun's butterfly diagram
  •              

    Käpylä, P. J., Mantere, M. J., & Brandenburg, A.: 2012, ``Cyclic magnetic activity due to turbulent convection in spherical wedge geometry,'' Astrophys. J. Lett. 755, L22 (arXiv:1205.4719, ADS, DOI, PDF)

    citations
    146 on ADS,
    161 on Google Scholar

          

    Inverse transfer even for nonhelical turbulence

  • Magnetically dominated turbulence
  • Nonhelical inverse transfer possible
  • k-2 inertial range spectrum
  • Wave turbulence coefficient CWT=1.9
  •              

    Brandenburg, A., Kahniashvili, T., & Tevzadze, A. G.: 2015, ``Nonhelical inverse transfer of a decaying turbulent magnetic field,'' Phys. Rev. Lett. 114, 075001 (arXiv:1404.2238, ADS, DOI, PDF, PDF)

    citations
    107 on ADS,
    95 on Google Scholar

          

    Detection of negative effective magnetic pressure instability in simulations

  • Conclusively demonstrates negative effective magnetic pressure instability(NEMPI)
  • is caused by magnetic suppression of turbulent pressure
  • reduction is stronger than added explicit pressure
  • argued to be relevant to formation of active regions
  •              

    Brandenburg, A., Kemel, K., Kleeorin, N., Mitra, D., & Rogachevskii, I.: 2011, ``Detection of negative effective magnetic pressure instability in turbulence simulations,'' Astrophys. J. Lett. 740, L50 (arXiv:1109.1270, ADS, DOI, HTML, PDF)

    citations
    56 on ADS,
    71 on Google Scholar

          

    Numerical Simulations of Gravitational Waves from Early-Universe Turbulence

  • Strongest efficiency for acoustic turbulence
  • Shallow low-frequency tail
  • Sharp drop above driving frequency
  • Same sign of GW circular polarization and magnetic helicity
  •              

    Roper Pol, A., Mandal, S., Brandenburg, A., Kahniashvili, T., & Kosowsky, A.: 2020, ``Numerical Simulations of Gravitational Waves from Early-Universe Turbulence,'' Phys. Rev. D 102, 083512 (arXiv:1903.08585, ADS, DOI, HTML, PDF)

    citations
    71 on ADS,
    44 on Google Scholar



    $Date: 2022/09/03 08:02:57 $, $Author: brandenb $, $Revision: 1.87 $