Observations and Modeling of Gravity Wave-Kelvin Helmholtz Instability (GW-KHI) Interactions in the Mesosphere and Lower Thermosphere: KHI Localization and Modulation by the GW Field

High frequency Gravity waves (GWs) promote mixing in the mesosphere and lower thermosphere (MLT) via energy transport and momentum deposition. Kelvin-Helmholtz instabilities (KHI) accompany strong shear throughout the atmosphere and influence GW breaking and mixing processes. Recent observations of GW-KHI interactions in the MLT revealed the formation of KHI tube and knot dynamics (T&K) that were reproduced in simulations of unperturbed shear layers. However, simulation studies to-date have not explored the dominant parameters of GW-KHI interactions and their mixing implications. We present observations and modeling results of KHI advecting through a stationary GW in the MLT. On 18 July 2018, the advanced mesospheric temperature mapper (AMTM) at Tierra del Fuego captured stationary 30-50 km GWs and orthogonal, 8-10 km KHI advecting through the wave field. We conduct direct numerical simulations (DNS) to assess the influence of shear layer depth and Richardson number (Ri) on GW-KHI interactions observed in the OH layer. DNS reveal the intensification and rapid evolution of KHI triggered by shear layer advection through successive GW phases. Shear layers initialized with Ri = 0.15 yield KHI localized to one GW wavelength, whereas KHI from layers with Ri = 0.05 form faster and extend across multiple GW wavelengths. For Ri = 0.05, T&K control the transition to turbulence for deeper shear layers, whereas shallower layers result in localized KH billow core breakdowns at earlier times. We assess the impact of these different KHI scales and shear intensities to determine how KHI-GW interactions promote mixing in different atmospheric environments.