The Influence of KHI Tube and Knot Dynamics on Gravity Wave/Shear-Induced Instabilities and Secondary Wave Generation

Kelvin Helmholtz Instability (KHI) tube and knot dynamics are a unique morphology of 3D shear instabilities that form when vortex "tubes" and "knots" connect spanwise-adjacent KHI billows occurring in the same streamwise shear. First identified in laboratory experiments by Thorpe 1987, KHI tubes and knots are facilitated by wide shear regions where adjacent KHI billows can form with different streamwise wavelengths (Thorpe 2002). Hecht et al 2021 recently captured the first atmospheric observations of KHI tube and knot dynamics in a wave-modulated shear layer, and the accompanying modeling study found that more rapid and intense vorticity evolution occurs in the tube and knot regions than in the adjacent KHI billow cores (Fritts et al. 2021). We postulate that these dynamics readily occur in strongly stratified layers throughout the atmosphere and may account for the discrepancy between modeled and observed vertical eddy diffusion in the lower thermosphere (Liu 2021; Garcia et al. 2014). To test this theory, we begin by evaluating tube and knot dynamics in a thermospheric KHI event captured by the recent 2018 Super Soaker campaign (Mesquita et al. 2020). We then examine these instability evolutions over a range of representative Reynolds numbers to determine their impact on turbulent mixing and secondary wave generation at different levels of the atmosphere. References: Fritts et al. 2021: https://doi.org/10.1029/2020JD033412 Garcia et al. 2014: https://doi.org/10.1002/2013JD021208 Hecht et al. 2021: https://doi.org/10.1029/2020JD033414 Liu 2021: https://doi.org/10.1029/2020GL091474 Mesquita et al. 2020: https://doi.org/10.1029/2020JA027972 Thorpe 1987: https://doi.org/10.1029/JC092iC05p05231 Thorpe 2002: https://doi.org/10.1256/00359000260247345