Rossby wave instability in weakly ionized protoplanetary discs – II. Radial B-fields

ABSTRACT In the first paper of this series, Paper I investigated the influence of pure azimuthal and vertical magnetic fields on the linear growth of the Rossby wave instability (RWI). In this second paper, we extend the analysis to examine the effect of radial magnetic fields on RWI modes, incorporating all three non-ideal magnetohydrodynamics (MHD) effects – Ohmic resistivity, Hall drift, and ambipolar diffusion. The presence of a radial magnetic field relies on the disc’s vertical shear and vertical magnetic field. We perform radially global linear analyses and solve the matrix eigenvalue problem using the spectral code Dedalus. It is found that in the ideal MHD limit, radial fields amplify the suppressive effect of vertical fields on RWI growth rates, with reductions starting at relatively weak field strengths ($\beta \sim 10^3{\!-\!}10^4$), applicable to protoplanetary discs. In the non-ideal MHD regime, when any of the three non-ideal effects become sufficiently strong, the growth rates revert to their hydrodynamic values.