Classification of coherent VSI modes as turbulence

Determine whether the coherent, wavelike modes of the Vertical Shear Instability can be classified as turbulence in the classical sense.

Background

The paper studies the Vertical Shear Instability (VSI) in protoplanetary disks and refers, for simplicity, to the associated non-Keplerian, non-laminar velocity field as “turbulence.” The authors explicitly distinguish this terminology from the classical concept of turbulence because VSI activity can consist of coherent, wave-like motions rather than conventional turbulent fluctuations.

The unresolved issue is whether these coherent VSI modes should genuinely be regarded as turbulence under the classical definition. The paper does not attempt to settle this conceptual classification and instead focuses on the modes’ ability to perturb and vertically redistribute dust.

References

Whether the VSI's coherent, wavelike modes themselves can be classified as turbulence in the classical sense remains unclear.

— Just a Phase? Weakening Vertical Shear Instability Explains Class II Disk Morphologies: Simulations with dust coagulation, sedimentation, thermal relaxation, and backreaction  (2609.28618 - Pfeil et al., 23 Sep 2026) in Section 1, Introduction