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Alexis Kaminski

Postdoctoral Scholar





Department Affiliation

Ocean Physics


B.S. Mechanical Engineering, University of Alberta (Edmonton, AB, Canada), 2010

M.S. Mechanical Engineering, University of Alberta (Edmonton, AB, Canada), 2012

Ph.D. Applied Mathematics & Theoretical Physics , Churchill College, University of Cambridge (Cambridge, UK), 2016


2000-present and while at APL-UW

Modal decomposition of polychromatic internal wave fields in arbitrary stratifications

Kaminski, A.K., and M.R. Flynn, "Modal decomposition of polychromatic internal wave fields in arbitrary stratifications," Wave Motion, 95, 102549, doi:10.1016/j.wavemoti.2020.102549, 2020.

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1 Jun 2020

Internal waves such as those produced by tidal sloshing over seafloor topography play an important role in the energy budget of the oceanic overturning circulation. Understanding their spatial and temporal structure, which depend on both the details of the forcing topography and the forcing frequency, is relevant in predicting how and where wave breaking and mixing may occur. Past work has largely focused on the case of a monochromatic wave field; however, the forcing tides may be composed of multiple frequency constituents. Here we present an approach by which the vertical mode structure of a polychromatic internal wave field may be computed from velocity timeseries data without any a priori knowledge of the details of the forcing topography. We consider wave fields in both uniform and vertically-varying stratification, and show using synthetic data that our approach is able to accurately reconstruct the vertical mode strengths. The sensitivity of our approach to noise and vertical resolution is also examined.

Acoustic observations of Kelvin-Helmholtz billows on an estuarine lutocline

Tu, J., D. Fan, Q. Lian, Z. Liu, W. Liu, A. Kaminski, and W. Smyth, "Acoustic observations of Kelvin-Helmholtz billows on an estuarine lutocline," J. Geophys. Res., 125, doi:10.1029/2019JC015383, 2020.

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1 Apr 2020

Kelvin‐Helmholtz (KH) instability plays an important role in turbulent mixing in deep oceans, coastal seas, and estuaries. Though widely observed and studied in thermohaline‐stratified waters, KH instability has only rarely been observed in sediment‐stratified environments. For the first time, we present direct observations of KH billows on an estuarine lutocline by combining echosounder images with velocity and density measurements. The interaction between velocity shear and the density stratification induced by suspended sediments initiated shear instabilities near the bed, indicated by gradient Richardson number (Ri) < 0.25 in the early stages of the observed billows. Once formed, the instabilities enhanced the vertical mixing of momentum, reducing vertical shear and elevating Ri. Linear instability analysis using measured velocity and density profiles well predicts the vertical location and spatial characteristics of the observed billows. These instabilities are believed to contribute to the vertical mixing, entrainment, and transport of estuarine and coastal sediments.

Stratified shear instability in a field of pre-existing turbulence

Kaminsky, A.K., and W.D. Smyth, "Stratified shear instability in a field of pre-existing turbulence," J. Fluid Mech., 862, 639-658, doi:, 2019.

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10 Mar 2019

Turbulent mixing of heat and momentum in the stably-stratified ocean interior occurs in discrete events driven by vertical variations of the horizontal velocity. Typically, these events have been modelled assuming an initially laminar stratified shear flow which develops wavelike instabilities, becomes fully turbulent, and then relaminarizes into a stable state. However, in the real ocean there is always some level of turbulence left over from previous events. Using direct numerical simulations, we show that the evolution of a stably-stratified shear layer may be significantly modified by pre-existing turbulence. The classical billow structure associated with Kelvin–Helmholtz instability is suppressed and eventually eliminated as the strength of the initial turbulence is increased. A corresponding energetics analysis shows that potential energy changes and dissipation of kinetic energy depend non-monotonically on initial turbulence strength, with the largest effects when initial turbulence is present but insufficient to prevent billow formation. The mixing efficiency decreases with increasing initial turbulence amplitude as the development of the Kelvin–Helmholtz billow, with its large pre-turbulent mixing efficiency, is arrested.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center