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Ren-Chieh Lien

Senior Principal Oceanographer

Affiliate Professor, Oceanography

Email

rcl@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

Publications

2000-present and while at APL-UW

Tides enhance the intensity of upwelling and water temperature oscillations in the cold dome region off northeastern Taiwan

Ho, C.-Y., H.-J. Lee, P.-C. Hsu, R.-C. Lien, and K.-H. Cheng, "Tides enhance the intensity of upwelling and water temperature oscillations in the cold dome region off northeastern Taiwan," Estuarine Coastal Shelf Sci., 314, doi:10.1016/j.ecss.2025.109127, 2025.

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1 Mar 2025

As the western boundary current in the North Pacific Ocean, the Kuroshio plays a key role in the marine environment around Taiwan. Over the past decades, extensive research and in situ observations have identified a cold dome and cold eddy off the northeastern coast of Taiwan, presumably influenced by the interaction between the Kuroshio and the complex topography. Satellite images of monthly sea surface temperature have revealed a prominent cold water mass in summer. Previous studies have not yet explained clearly the formation mechanism of this cold dome. In this study, we used the Massachusetts Institute of Technology General Circulation Model to identify the mechanisms underlying the formation of this cold dome off the northeastern coast of Taiwan. Various scenarios were simulated to determine the primary causes of cold water upwelling in the cold dome region. Model results at 50-m depth revealed that a cold dome, 4°C–5°C cooler than the Kuroshio, was formed off the northeastern coast of Taiwan where the Kuroshio impinged. However, the model's temperature drop 1°C in the surface layer falls short of field observations and satellite images, 5°C. Including effects of wind stress in the model showed that the summer monsoon may increase the cold-dome area, but not the surface temperature drops. Including tides in the model accurately simulates the observed near surface temperature drop of 5°C–6°C. Model temperature exhibits periodic variations. Spectral analysis of model temperature revealed spectral peaks at diurnal, semidiurnal tidal and 14-day periods.

Coherent float arrays for near-inertial wave studies

Girton, J.B., C.B. Whalen, R.-C. Lien, and E. Kunze, "Coherent float arrays for near-inertial wave studies," Oceanography, 37, 58-67, doi:10.5670/oceanog.2024.306, 2024.

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1 Dec 2024

Rapid changes in winds drive rotating currents known as inertial oscillations. In a stratified ocean, these oscillations can then initiate subsurface near-​inertial internal waves that propagate laterally and vertically and are refracted by horizontal gradients in vorticity. We report on a process study of wind forcing and ocean response in the Iceland Basin of the North Atlantic using arrays of profiling floats measuring temperature, salinity, horizontal velocity, and turbulence. Three arrays with four to eight floats each sampled spatial gradients in both high-frequency (internal wave) and low-frequency (mesoscale) currents in order to clarify the dynamical coupling between these distinct categories of oceanic phenomena.

The observations are qualitatively consistent with theory for wave-​mesoscale interactions: immediately following each wind event, a surface inertial oscillation appears that initially matches a simple slab mixed-layer model in both amplitude and phase, but diverges over several cycles to become a super-inertial internal wave. The surface oscillation decays over several days, while near-inertial energy appears below the surface layer two to three days after the surface motion. Lateral phase gradients estimated from the inertial cycle at each float show that the deeper energy has shorter horizontal wavelengths and tends to propagate toward anticyclonic (negative) vorticity.

These case studies illustrate both the strengths and limitations of Lagrangian (flow-following) arrays for the study of the energetics of air-sea interaction. High-resolution observations of this kind are not feasible globally, but examples in a variety of wind and ocean eddy environments can improve our understanding and verify estimates of wind-energy input and mixing from numerical models and theory.

Near-inertial energy variability in a strong mesoscale eddy field in the Iceland Basin

Voet, G., and 13 others including H.L. Simmons, C.B. Whalen, R.-C. Lien, and J.B. Girton, "Near-inertial energy variability in a strong mesoscale eddy field in the Iceland Basin," Oceanography, 37, 34-47, doi:10.5670/oceanog.2024.302, 2024.

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1 Dec 2024

An 18-month deployment of moored sensors in Iceland Basin allows characterization of near-inertial (frequencies near the Coriolis frequency f with periods of ~14 h) internal gravity wave generation and propagation in a region with an active mesoscale eddy field and strong seasonal wind and heat forcing. The seasonal cycle in surface forcing deepens the mixed layer in winter and controls excitation of near-​inertial energy. The mesoscale eddy field modulates near-inertial wave temporal, horizontal, and vertical scales, as well as propagation out of the surface layer into the deep permanent pycnocline. Wind-forced near-inertial energy has the most active downward propagation within anticyclonic eddies. As oceanic surface and bottom boundaries act to naturally confine the propagation of internal waves, the vertical distribution of these waves can be decomposed into a set of "standing" vertical modes that each propagate horizontally at different speeds. The lowest modes, which propagate quickly away from their generation sites, are most enhanced when the mixed layer is deep and are generally directed southward.

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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