Kelvin-Helmholtz Instability "Tube" and "Knot" Dynamics. Part II: KHI T&K Dynamics in a Multiscale Gravity Wave Direct Numerical Simulation

A companion paper by Fritts et al. reviews evidence for Kelvin-Helmholtz instability (KHI) "tube" and "knot" (T&K) dynamics that appear to be widespread throughout the atmosphere. Here we describe the results of an ide-alized direct numerical simulation of multiscale gravity wave dynamics that reveals multiple larger-and smaller-scale KHI T&K events. The results enable assessments of the environments in which these dynamics arise and their competition with concurrent gravity wave breaking in driving turbulence and energy dissipation. A larger-scale event is diagnosed in detail and reveals diverse and intense T&K dynamics driving more intense turbulence than occurs due to gravity wave breaking in the same environment. Smaller-scale events reveal that KHI T&K dynamics readily extend to weaker, smaller-scale, and increasingly viscous shear flows. Our results suggest that KHI T&K dynamics should be widespread, perhaps ubiquitous, wherever superposed gravity waves induce intensifying shear layers, because such layers are virtually always present. A second companion paper demonstrates that KHI T&K dynamics exhibit elevated turbulence generation and energy dissi-pation rates extending to smaller Reynolds numbers for relevant KHI scales wherever they arise. These dynamics are sug-gested to be significant sources of turbulence and mixing throughout the atmosphere that are currently ignored or underrepresented in turbulence parameterizations in regional and global models.