Critical layer position and axial spiral dynamics in strato-rotational instability

This paper investigates the strato-rotational instability (SRI) in a stably stratified Taylor–Couette (TC) system, a canonical model for understanding angular momentum transport in astrophysical accretion disks. Although the instability is known to arise from the interaction of rotation and stratification, the fundamental mechanisms remain debated. Using direct numerical simulations, we analyze the evolution of the non-axisymmetric spiral flow, focusing on dynamic transitions in its axial propagation direction. Our analysis reveals that the reversals in spiral direction are directly associated with the formation and inversion of distinct local circulation cells. By qualitatively comparing the fluid dynamics with the positions of critical layers, we observe that the classical critical layer appears to absorb or over-reflect flow disturbances, whereas the baroclinic critical layers confine the circulation cells, suggesting a feedback mechanism between wave-mean flow interactions and the large-scale circulation. We further investigate the role of the rigid outer boundary by systematically increasing the gap size, finding that larger gaps can change the onset of the instability, and maybe even suppress it, though it can be recovered with stronger stratification. • Axial reversals of SRI spirals link to large-scale circulation changes. • Waves confined by baroclinic layers; position matches mean-flow inflection. • Observed dynamics indicate feedback between critical layers and circulation.