Parametric Study of the Rossby Wave Instability in a Two-dimensional Barotropic Disk II: Non-Linear Calculations

TL;DR

This study uses non-linear simulations to analyze vortex formation via Rossby Wave Instability in 2D protoplanetary disks, revealing vortex evolution, mergers, and stable configurations relevant to observed disk structures.

Contribution

It presents the first non-linear numerical simulations of RWI in 2D disks with detailed analysis of vortex formation, evolution, and empirical relations to initial conditions.

Findings

Multiple vortices form and merge into a single stable vortex.

The final vortex migrates inward and approaches a marginally stable state.

Empirical relations link vortex properties to initial disk conditions.

Abstract

Vortices in protoplanetary disks have attracted attention since the discovery of lopsided structures. One of the possible mechanisms for producing vortices is the Rossby Wave Instability (RWI). In our previous work, we have performed detailed linear stability analyses of the RWI with various initial conditions. In this paper, we perform numerical simulations of the vortex formation by the RWI in 2D barotropic disks using the Athena++ code. As initial conditions, we consider axisymmetric disks with a Gaussian surface density bump of various contrasts and half-widths. Perturbations grow as expected from the linear stability analyses in the linear and weakly non-linear regimes. After the saturation, multiple vortices are formed in accordance with the most unstable azimuthal mode and coalesce one after another. In the end, only one quasi-stationary vortex (the RWI vortex) remains, which migrates inward. During the RWI evolution, the axisymmetric component approaches the stable configuration. We find that the axisymmetric component reaches the marginally stable state for the most unstable azimuthal mode at the saturation and the marginally stable state for the m = 1 mode at the final vortex merger. We investigate the structure and evolution of the RWI vortices. We obtain some empirical relations between the properties of the RWI vortices and the initial conditions. Using tracer particle analyses, we find that the RWI vortex can be considered as a physical entity like a large fluid particle. Our results provide a solid theoretical ground for quantitative interpretation of the observed lopsided structures in protoplanetary disks.