Wavelike nature of the vertical shear instability in global protoplanetary discs

Abstract

The vertical shear instability (VSI) is a robust phenomenon in irradiated protoplanetary discs (PPDs). The majority of previous numerical simulations have focused on the turbulent properties of its saturated state. However, the saturation of the VSI manifests as large-scale coherent radially travelling inertial waves. In this paper, we study inertial-wave-disc interactions and their impact on VSI saturation. Inertial-wave linear theory is developed and applied to a representative global 2D simulation using the athena++ code. It is found that the VSI saturates by separating the disc into several radial wave zones roughly demarcated by Lindblad resonances (turning points); this structure also manifests in a modest radial variation in the vertical turbulence strength. Future numerical work should employ large radial domains to accommodate this radial structure of the VSI, while concurrently adopting sufficiently fine resolutions to resolve the parametric instability that attacks the saturated VSI inertial waves.