Kelvin‐Helmholtz Billow Interactions and Instabilities in the Mesosphere Over the Andes Lidar Observatory: 2. Modeling and Interpretation

Abstract

AbstractA companion paper by Hecht et al. (2020, https://doi.org/10.1002/2014JD021833) describes high‐resolution observations in the hydroxyl (OH) airglow layer of interactions among adjacent Kelvin‐Helmholtz instabilities (KHI). The interactions in this case were apparently induced by gravity waves propagating nearly orthogonally to the KHI orientations, became strong as Kelvin‐Helmholtz (KH) billows achieved large amplitudes, and included features named “tubes” and “knots” in early laboratory KHI studies. A numerical modeling study approximating the KHI environment and revealing the dynamics of knots and tubes is described here. These features arise where KH billows are misaligned along their axes or where two billows must merge with one. They bear a close resemblance to the observed instability dynamics and suggest that they are likely to occur wherever KHI formation is modulated by variable wind shears, stability, or larger‐scale motions. Small‐scale features typical of those in turbulence develop in association with the formation of the knots and tubes earlier and more rapidly than those accompanying individual billows, supporting an earlier conjecture that tubes and knots are commonly major sources of intense turbulent dissipation accompanying KHI events in the atmosphere.