Rossby vortices in thin magnetized accretion discs

We study the Rossby wave instability (RWI) in a thin accretion disc threaded by an initially toroidal magnetic field using the magnetohydrodynamics (MHD) code PLUTO. We find that for plasma $10^1 10^3$ the magnetic field has negligible effect. The initially toroidal field is twisted inside the vortex and expelled at late times. This creates a radially directed field outside the vortex region, which can be understood via a simple kinematic model of a magnetic field in a rotating fluid. The twisted field may affect planet formation by changing the rate of dust trapping in the vortex and may be observable via polarized dust emission.