Henrik Latter, Pierre Lesaffre, Steven A. Balbus

MNRAS (2009), 394, 715

Local simulations of the magnetorotational instability (MRI) in accretion discs can exhibit recurrent coherent structures called channel flows. The formation and destruction of these structures may play a role in the development and saturation of MRI-induced turbulence, and consequently help us understand the time-dependent accretion behaviour of certain astrophysical objects. We investigate instabilities which can destroy the channel flows and show how they relate to the classical instabilities of plasma physics, the kink and pinch modes.

Pierre Lesaffre, Steven A. Balbus, Henrik Latter

MNRAS (2009), 396, 779

We run mean-field shearing-box numerical simulations with a temperature-dependent resistivity and compare them to a reduced dynamical model. Our simulations reveal the co-existence of two quasi-steady states, a `quiet' state and an `active' turbulent state, confirming the predictions of the reduced model.

Henrik N. Latter, Steven A. Balbus

MNRAS (2009), 399, 1058

We study the interaction between non-axisymmetric inertial waves and their corotation resonances in a hydrodynamical disc. Because inertial waves can sometimes manifest as discrete trapped standing modes, it is often hypothesized that their oscillations are affiliated with the poorly understood quasi-periodic oscillation (QPO) phenomenon. We demonstrate that a large class of non-axisymmetric three-dimensional (3D) inertial waves cannot manifest as trapped normal modes.

Christophe J.P. Gissinger

Euro.Phys.Lett. 87, 39002(2009)

We present numerical simulations of the magnetic field generated by the flow of liquid sodium driven by two counter-rotating impellers (VKS experiment). Using a kinematic code in cylindrical geometry, it is shown that different magnetic modes can be generated depending on the flow configuration. While the time-averaged axisymmetric mean flow generates an equatorial dipole, our simulations show that an axial field of either dipolar or quadrupolar symmetry can be generated by taking into account non-axisymmetric components of the flow. Moreover, we show that by breaking a symmetry of the flow, the magnetic field becomes oscillatory. This leads to reversals of the axial dipole polarity, involving a competition with the quadrupolar component.

Henrik Latter, Gordon Ogilvie

Icarus (2009), 202, 565

We aim to explain both the periodic microstructure on 150-220m and irregular variations on 1-10km in Saturn's A and B-ring. We propose that the former structures correspond to the peaks and troughs of the nonlinear wavetrains that form naturally in a viscously overstable disk. The latter variations on longer scales may correspond to modulations and defects in the wavetrains' amplitudes and wavelength.

Steven A.  Balbus, Julius Bonart, Henrik Latter, Nigel Weiss

MNRAS, 400, 176

We show that the differential rotation profile of the solar convection zone, apart from inner and outer boundary layers, can be reproduced with great accuracy if the isorotation contours correspond to characteristics of the thermal wind equation. This requires that there be a formal quantitative relationship involving the entropy and the angular velocity. Earlier work has suggested that this could arise from magnetohydrodynamic stability constraints; here, we argue that purely hydrodynamical processes could also lead to such a result.

Danail Obreschkow, Hans-Rainer Klöckner, Ian Heywood, François Levrier, Steve Rawlings

ApJ (2009), 703, 1890

We present a sky simulation of the atomic HI-emission line and the first 10 12-CO rotational emission lines of molecular gas in galaxies beyond the Milky Way. 

Steve Balbus

in Physical Processes in Circumstellar Disks Around Young Stars, ed. P. Garcia, (University of Chicago Press: Chicago)

The magnetohydrodynamical behavior (MHD) of accretion disks is reviewed. A detailed presentation of the fundamental MHD equations appropriate for protostellar disks is given.

Tamara Bogdanovic, Chris S. Reynolds, Steven A. Balbus, Ian J. Parrish

ApJ, 704, 211

We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the 3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture the effects of anisotropic heat conduction along the lines of magnetic field, but do not account for the cosmological setting of clusters or the presence of AGN.