Multi-Scale Kelvin-Helmholtz Instability Dynamics Observed by PMC Turbo on 12 July 2018: 1. Secondary Instabilities and Billow Interactions

C. Bjorn Kjellstrand, David C. Fritts, Amber D. Miller, Bifford P. Williams, Natalie Kaifler, Christopher Geach, Shaul Hanany, Bernd Kaifler, Glenn Jones, Michele Limon, Jason Reimuller, Ling Wang

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4 Scopus citations


The Polar Mesospheric Cloud (PMC) Turbulence experiment performed optical imaging and Rayleigh lidar PMC profiling during a 6-day flight in July 2018. A mosaic of seven imagers provided sensitivity to spatial scales from ∼20 m to 100 km at a ∼2-s cadence. Lidar backscatter measurements provided PMC brightness profiles and enabled definition of vertical displacements of larger-scale gravity waves (GWs) and smaller-scale instabilities of various types. These measurements captured an interval of strong, widespread Kelvin-Helmholtz instabilities (KHI) occurring over northeastern Canada on July 12, 2018 during a period of significant GW activity. This paper addresses the evolution of the KHI field and the characteristics and roles of secondary instabilities within the KHI. Results include the imaging of secondary KHI in the middle atmosphere and multiple examples of KHI “tube and knot” (T&K) dynamics where two or more KH billows interact. Such dynamics have been identified clearly only once in the atmosphere previously. Results reveal that KHI T&K arise earlier and evolve more quickly than secondary instabilities of uniform KH billows. A companion paper by Fritts et al. (2022), reveals that they also induce significantly larger energy dissipation rates than secondary instabilities of individual KH billows. The expected widespread occurrence of KHI T&K events may have important implications for enhanced turbulence and mixing influencing atmospheric structure and variability.

Original languageEnglish (US)
Article numbere2021JD036232
JournalJournal of Geophysical Research Atmospheres
Issue number18
StatePublished - Sep 27 2022

Bibliographical note

Funding Information:
The PMC‐turbo mission was funded by NASA Contract 80NSSC18K0050 and supported by NSF grant AGS‐2032678. This project also received funding from the German Aerospace Center (DLR) for construction, integration, and operation of the Rayleigh lidar and subsequent data analyses.

Publisher Copyright:
© 2022. American Geophysical Union. All Rights Reserved.


  • KHI knots and tubes
  • Kelvin-Helmholtz instability
  • instabilities and turbulence
  • multi-scale dynamics
  • secondary KHI


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