Research highlights and influential papers

recent research highlights

Distributed Solar Dynamo

  • Solar dynamo may not be located in the tachocline
  • Equatorward migration from negative near-surface shear
  • Non-resistively limited saturation through helicity fluxes
  • Bipolar regions formed locally near the surface
  • Tilt depends just on shear, not on helicity
  • Large-scale fields even without helicity, just shear

    Brandenburg, A.: 2005, ``The case for a distributed solar dynamo shaped by near-surface shear,'' Astrophys. J. 625, 539-547 (astro-ph/0502275, ADS, PDF)

    313 on ADS


    Dynamo Review

  • Reviews small scale and large scale dynamos
  • Saturation through magnetic helicity conservation
  • Detailed calculation of transport coefficiens using minimal tau approximation (MTA)

    Brandenburg, A., & Subramanian, K.: 2005, ``Astrophysical magnetic fields and nonlinear dynamo theory,'' Phys. Rep. 417, 1-209 (astro-ph/0405052, ADS, PDF)

    1189 on ADS


    Accretion disc turbulence

  • first simulation showing that turbulence can be driven by the Balbus-Hawley (or magnetorotational) instability by a magnetic field that in turn is generated by this very same turbulence
  • establishes self-consistent value for disc viscosity with Shakura-Sunyaev alpha of about 0.01

    Brandenburg, A., Nordlund, Å., Stein, R. F., & Torkelsson, U.: 1995, ``Dynamo-generated turbulence and large-scale magnetic fields in a Keplerian shear flow,'' Astrophys. J. 446, 741-754 (ADS, PDF)

    713 on ADS


    Inverse cascade: resistively slow

  • establishes fundamental connection between inverse cascade in hydromagnetic turbulence and alpha effect in dynamo theory
  • unexpected: inverse cascade operates on resistive timescale
  • has to do with magnetic helicity conservation

    Brandenburg, A.: 2001, ``The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence,'' Astrophys. J. 550, 824-840 (astro-ph/0006186, ADS, PDF)

    448 on ADS


    Mixed parity dynamo solutions

  • first simulation showing stable mixed parity solutions of nonlinear dynamo equations
  • relevant for Maunder minima type variations of solar/stellar activity

    Brandenburg, A., Krause, F., Meinel, R., Moss, D., & Tuominen, I.: 1989, ``The stability of nonlinear dynamos and the limited role of kinematic growth rates,'' Astron. Astrophys. 213, 411-422 (ADS, PDF)

    180 on ADS


    Convective Dynamo Simulations with Overshoot

  • it was previously though that magnetic buoyancy removes magnetic flux before the dynamo has a chance to work
  • we find that downward pumping is at least equally strong
  • the dynamo works in the entire convection zone, but pumping concentrates magnetic flux at the bottom of the convection zone
  • relevant to the sun

    Nordlund, Å., Brandenburg, A., Jennings, R. L., Rieutord, M., Ruokolainen, J., Stein, R. F., & Tuominen, I.: 1992, ``Dynamo action in stratified convection with overshoot,'' Astrophys. J. 392, 647-692 (ADS, PDF)

    223 on ADS

    Brandenburg, A., Jennings, R. L., Nordlund, Å., Rieutord, M., Stein, R. F., & Tuominen, I.: 1996, ``Magnetic structures in a dynamo simulation,'' J. Fluid Mech. 306, 325-352 (ADS, PDF)

    194 on ADS


    Galactic Magnetism Review

  • reviews observations and theory
  • has now become standard reference

    Beck, R., Brandenburg, A., Moss, D., Shukurov, A., & Sokoloff, D.: 1996, ``Galactic Magnetism: Recent Developments and Perspectives,'' Ann. Rev. Astron. Astrophys. 34, 155-206 (ADS, PDF)

    828 on ADS


    Early Universe magnetic fields

  • First to point out possibility of inverse cascade in early Universe
  • Magnetic fields from electroweak phase transition otherwise small scale
  • Horizon scale ~3 cm, corresponding to ~AU after cosmological expansion
  • Would become ~kpc with inverse cascade

    Brandenburg, A., Enqvist, K., & Olesen, P.: 1996, ``Large-scale magnetic fields from hydromagnetic turbulence in the very early universe,'' Phys. Rev. D 54, 1291-1300 (astro-ph/9602031, ADS, PDF)

    239 on ADS

    Christensson, M., Hindmarsh, M., & Brandenburg, A.: 2001, ``Inverse cascade in decaying 3D magnetohydrodynamic turbulence,'' Phys. Rev. E 64, 056405, 1-6 (astro-ph/0011321, ADS, PDF)

    177 on ADS


    SN-driven turbulence

  • first realistic 3-D simulation of supernova-driven multi-phase interstellar medium
  • find segregation into 2 phases: warm/denser and hot/dilute and gives filling factors
  • demonstrates different rms velocities in warm (~10 km/s) and hot (~40 km/s) components

    Korpi, M. J., Brandenburg, A., Shukurov, A., Tuominen, I., & Nordlund, Å.: 1999, ``A supernova regulated interstellar medium: simulations of the turbulent multiphase medium,'' Astrophys. J. Lett. 514, L99-L102 (ADS, PDF)

    171 on ADS


    Nonhelical MHD turbulence

  • Demonstrates Rm1/2 scaling of growth rate
  • Establishes a k+3/2 spectrum during kinematic stage
  • Inertial range with k−3/2 magnetic and kinetic energy spectrum during saturated stage

    Haugen, N. E. L., Brandenburg, A., & Dobler, W.: 2004, ``Simulations of nonhelical hydromagnetic turbulence,'' Phys. Rev. E 70, 016308, 1-14 (astro-ph/0307059, ADS, PDF)

    271 on ADS


    Stellar cycle periods

  • Inactive (I), Active (A), and Superactive (S) branches
  • I and A branches separated by factor 6
  • Computed cycle periods often match observed ones
  • Postive slope: cycle frequency increases faster than rotation rate

    Saar, S. H., & Brandenburg, A.: 1999, ``Time evolution of the magnetic activity cycle period. II. Results for an expanded stellar sample,'' Astrophys. J. 524, 295-310 (ADS, PDF) - citations 261 on ADS

    Brandenburg, A., Saar, S. H., & Turpin, C. R.: 1998, ``Time evolution of the magnetic activity cycle period,'' Astrophys. J. Lett. 498, L51-L54 (ADS, PDF) - citations - 118 on ADS

    Brandenburg, A., Mathur, S., & Metcalfe, T. S.: 2017, ``Evolution of coexisting long and short period stellar activity cycles,'' Astrophys. J. 845, 79 (arXiv:1704.09009, ADS, DOI, PDF) - citations - 53 on ADS


    Global simulation of fully convective star

  • 3-D simulation of sphere in a box
  • Demonstrates dynamo action in fully convective star
  • Large scale field dipolar
  • Anti-solar rotation, constant along cylinders

    Dobler, W., Stix, M., & Brandenburg, A.: 2006, ``Convection and magnetic field generation in fully convective spheres,'' Astrophys. J. 638, 336-347 (astro-ph/0410645, ADS, PDF)

    184 on ADS

    $Date: 2022/09/03 08:02:57 $, $Author: brandenb $, $Revision: 1.149 $