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Ren-Chieh Lien

Senior Principal Oceanographer

Affiliate Professor, Oceanography

Email

lien@apl.uw.edu

Phone

206-685-1079

Research Interests

Turbulence, Internal waves, Vortical motions, Surface mixed layer and bottom boundary layer dynamics, Internal solitary waves, Small-scale vorticity, Inertial waves

Biosketch

Dr. Lien is a physical oceanographer specializing in internal waves, vortical motions, and turbulence mixing in the upper ocean and their effects on upper ocean heat, salinity, momentum, and energy budgets. His primary scientific research interests include: (1) upper ocean internal waves and turbulence, especially in tropical Pacific and Indian oceans, (2) strongly nonlinear internal solitary wave energetics and breaking mechanisms, (3) small-scale vortical motions, and (4) bottom boundary layer turbulence. He is especially interested in understanding the modulation of internal waves and turbulence mixing by large-scale processes, as well as the effects of small-scale processes and large-scale flows.

One of Dr. Lien most important findings is the strong modulation of turbulence mixing by large-scale equatorial processes, such as tropical instability waves and Kelvin waves, in the eastern equatorial Pacific. He is especially interested in small-scale, potential vorticity motions — the vortical mode, which operates on the same scale as internal waves — and their effects on turbulence mixing and stirring. Lien has led sea-going experiments in the Pacific and Indian oceans and the South China Sea, using a variety of instruments including microstructure profilers, Lagrangian floats, EM-APEX floats, and moorings. He also developed a real-time towed CTD chain system, designed to study small-scale water mass variability in the upper ocean at a vertical and horizontal resolution of O(1 m).

Lien mentors and supervises masters and doctoral students and postdocs. His research and experiments have been funded primarily by the National Science Foundation, the Office of Naval Research, and National Oceanic and Atmospheric Administration.

Department Affiliation

Ocean Physics

Education

B.S. Marine Science, Chinese Culture University, 1978

M.S. Physical Oceanography, University of Hawaii, 1986

Ph.D. Physical Oceanography, University of Hawaii, 1990

Projects

Lateral Mixing

Small scale eddies and internal waves in the ocean mix water masses laterally, as well as vertically. This multi-investigator project aims to study the physics of this mixing by combining dye dispersion studies with detailed measurements of the velocity, temperature and salinity field during field experiments in 2011 and 2012.

1 Sep 2012

Publications

2000-present and while at APL-UW

Island Arc Turbulent Eddy Regional Exchange (ARCTERX): Science and Experiment Plan

The ARCTERX Team, "Island Arc Turbulent Eddy Regional Exchange (ARCTERX): Science and Experiment Plan," Technical Report, APL-UW TR 2201. Applied Physics Laboratory, University of Washington, July 2022, 49 pp.

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15 Jul 2022

Submesoscale flows such as fronts, eddies, filaments, and instabilities with lateral dimensions between 100 m and 10 km are ubiquitous features of the ocean. They act as an intermediary between the mesoscale and small-scale turbulence and are thought to have a critical role in closing the ocean's kinetic budget by facilitating a forward energy cascade, where energy is transferred to small scales and dissipated.

The initiative uses a suite of measurements from autonomous platforms and ships combined with regional simulations to characterize the submesoscale flows in the western Pacific Ocean between Luzon and Mariana Island arcs &$151; the ARCTERX region.

Program goals are to characterize the strength and spectral properties of the turbulent cascade of kinetic energy on the submesoscales in the ARCTERX study region and understand the processes that control energy transfers across scales and their seasonal variability.

Near-inertial wave interactions and turbulence production in a Kuroshio anticyclonic eddy

Essink, S., E. Kunze, R.-C. Lien, R. Inoue, and S. Ito, "Near-inertial wave interactions and turbulence production in a Kuroshio anticyclonic eddy," J. Phys. Oceanogr., 52, 2687-2704, doi:10.1175/JPO-D-21-0278.1, 2022.

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21 Jun 2022

Interactions between near-inertial waves and the balanced eddy field modulate the intensity and location of turbulent dissipation and mixing. Two EM-APEX profiling floats measured near-inertial waves generated by typhoons (i) Mindulle, 22 August 2016, and (ii) Lionrock, 30 August 2016, near the radius of maximum velocity of a mesoscale anticyclonic eddy in the Kuroshio–Oyashio Confluence east of Japan. High-vertical-wavenumber near-inertial waves exhibit energy-fluxes inward toward eddy center, consistent with wave refraction/reflection at the eddy perimeter. Near-inertial kinetic energy tendencies are nearly two orders of magnitude greater than observed turbulent dissipation rates ε, indicating propagation/advection of wave packets in and out of the measurement windows. Between 50–150 m, ε ~ O(10-10 W kg-1) , more than an order of magnitude weaker than outside the eddy, pointing to near-inertial wave breaking at different depths or eddy radii. Between 150–300 m, small-scale inertial-period patches of intense turbulence with near-critical Ri occur where comparable near-inertial and eddy shears are superposed. Three-dimensional ray-tracing simulations show that wave dynamics at the eddy perimeter are controlled by radial gradients in vorticity and Doppler-shifting with much weaker contributions from vertical gradients, stratification and sloping isopycnals. Surface-forced waves are initially refracted downward and inward, consistent with the observed energy-flux. A turning-point shadow zone is found in the upper pycnocline, consistent with weak observed dissipation rates. In summary, the geometry of wave/mean flow interaction creates a shadow zone of weaker near-inertial waves and turbulence in the upper part while turning-point reflections amplify wave shear leading to enhanced dissipation rates in the lower part of the eddy.

Shear instability and turbulent mixing in the stratified shear flow behind a topographic ridge at high Reynolds number

Chen, J.-L., X. Yu, M.-H. Chang, S. Jan, Y.J. Yang, and R.-C. Lien, "Shear instability and turbulent mixing in the stratified shear flow behind a topographic ridge at high Reynolds number," Front. Mar. Sci., 9, doi:10.3389/fmars.2022.829579, 2022.

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18 May 2022

Observations on the lee of a topographic ridge show that the turbulence kinetic energy (TKE) dissipation rate due to shear instabilities is three orders of magnitude higher than the typical value in the open ocean. Laboratory-scale studies at low Reynolds number suggest that high turbulent dissipation occurs primarily within the core region of shear instabilities. However, field-scale studies indicate that high turbulence is mainly populated along the braids of shear instabilities. In this study, a high-resolution, resolving the Ozmidov-scale, non-hydrostatic model with Large Eddy Simulation (LES) turbulent closure is applied to investigate dominant mechanisms that control the spatial and temporal scales of shear instabilities and resulting mixing in stratified shear flow at high Reynolds number. The simulated density variance dissipation rate is elevated in the cusp-like bands of shear instabilities with a specific period, consistent with the acoustic backscatter taken by shipboard echo sounder. The vertical length scale of each cusp-like band is nearly half of the vertical length scale of the internal lee wave. However, it is consistent with instabilities originating from a shear layer based on linear stability theory. The model results indicate that the length scale and/or the period of shear instabilities are the key parameters to the mixing enhancement that increases with lateral Froude number FrL, i.e. stronger shear and/or steeper ridge.

More Publications

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
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