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Kelvin Helmholtz tube and knot (KH T/K) dynamics are a subclass of 3D shear instabilities that form when vortex "tubes" and "knots" connect adjacent, misaligned KH billows in a shear layer. While the existence of KH T/K was demonstrated in laboratory experiments by Thorpe 1987, they have only recently been observed in airglow images in the atmosphere (Hecht et al., 2021). Modeling studies by Fritts et al., 2021 determined that tubes and knots yield accelerated vorticity evolution and elevated dissipation rates in KH shear turbulence events, suggesting significant impacts to local mixing anywhere KH T/K dynamics occur. In this study, we present modeling results of T/K dynamics accompanying a thermospheric KH event captured by the 2018 Super Soaker campaign (Mesquita et al., 2020). Chemical tracers released by a rocketsonde on 26 January 2018 showed a coherent KH instability near 102 km that rapidly deteriorated within 45-90 s. Using wind and temperature data from the event, we conducted high resolution DNS employing both wide and narrow spanwise domains to facilitate (wide domain case) and prohibit (narrow domain case) the axial deformation of KH billows that allows tubes and knots to form. KH T/K dynamics are shown to produce accelerated instability evolution consistent with the observations, achieving peak dissipation rates 2.5 times larger and 2.4 buoyancy periods faster than in the case prohibiting T/K. The results suggest that enhanced mixing from thermospheric KH T/K events could account for the discrepancy between modeled and observed vertical eddy diffusion in the lower thermosphere (Liu 2021; Garcia et al., 2014) and merits further study. 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/10.1029/2020GL091474Mesquita et al., 2020: https://doi.org/10.1029/2020JA027972 Thorpe 1987: https://doi.org/10.1029/JC092iC05p05231 |
