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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

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.

Two-dimensional wavenumber spectra on the horizontal submesoscale and vertical finescale

Vladoiu, A., R.-C. Lien, and E. Kunze, "Two-dimensional wavenumber spectra on the horizontal submesoscale and vertical finescale," J. Phys. Oceanogr., EOR, doi:10.1175/JPO-D-21-0111.1, 2022.

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12 May 2022

Horizontal and vertical wavenumbers (kx, kz) immediately below the Ozmidov wavenumber are spectrally distinct from both isotropic turbulence (kx, kz > 1 cpm) and internal waves as described by the Garrett-and-Munk (GM) model spectrum (kz < 0.1 cpm). Towed CTD chain, augmented with concurrent EM-APEX profiling float microstructure measurements and shipboard ADCP surveys, are used to characterize 2D wavenumber (kx, kz) spectra of isopycnal slope, vertical strain and isopycnal salinity-gradient on horizontal wavelengths of 50 m – 250 km and vertical wavelengths of 2 – 48 m. For kz < 0.1 cpm, 2D spectra of isopycnal slope and vertical strain resemble GM. Integrated over the other wavenumber, the isopycnal slope 1D kx spectrum exhibits a roughly + 1/3 slope for kx > 3 x 10-3 cpm, and the vertical strain 1D kz spectrum a –1 slope for kz > 0.1 cpm, consistent with previous 1D measurements, numerical simulations and anisotropic stratified turbulence theory. Isopycnal salinity-gradient 1D kx spectra have a + 1 slope for kx > 2 x 10-3 cpm, consistent with nonlocal stirring. Turbulent diapycnal diffusivities inferred in the (i) internal-wave subrange using a vertical strain-based finescale parameterization are consistent with those inferred from finescale horizonal wavenumber spectra of (ii) isopycnal slope and (iii) isopycnal salinity-gradients using Batchelor model spectra. This suggests that horizontal submesoscale and vertical finescale subranges participate in bridging the forward cascade between weakly nonlinear internal waves and isotropic turbulence, as hypothesized by anisotropic turbulence theory.

Three‑dimensional perspective on a convective instability and transition to turbulence in an internal solitary wave of depression shoaling over gentle slopes

Rivera-Rosario, G., P.J. Diamessis, R.-C. Lien, K.G. lamb, and G.N. Thomsen, "Three‑dimensional perspective on a convective instability and transition to turbulence in an internal solitary wave of depression shoaling over gentle slopes," Environ. Fluid Mech., EOR, doi:10.1007/s10652-022-09844-7, 2022.

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4 Mar 2022

The shoaling of an internal solitary wave (ISW) of depression is explored in three-dimensions (3D) through high-accuracy, fully nonlinear, and nonhydrostatic simulations. Time-averaged background stratification and current profiles from field observations, along with measured bathymetry data from the South China Sea (SCS), are used. The computational approach is based on a high-resolution and high-accuracy deformed spectral multidomain penalty method incompressible flow solver. Recent field observations in the SCS indicate the presence of a convective instability followed by a subsurface recirculating core that may persist for more than tens of km and drive turbulent-induced mixing, estimated to be up to four orders of magnitude larger than that typically found in the ocean. The preceding convective instability occurs due to a sudden decrease in the wave propagation speed, below the maximum horizontal wave-induced velocity, and possible from the stretching of the near-surface vorticity layer of the baroclinic background current from the propagating ISW. Motivated by such observations, the present study examines the onset of the 3D convective instability that results in subsurface recirculating core formation, as the ISW propagates and shoals in the normal-to-isobath direction. A noise field is inserted in the wave-induced velocity and density field to force the evolution in 3D. The initial instability has a transitional structure that develops in the lateral direction. The evolution of the lateral instability and subsequent transition to turbulence in the breaking wave is compared with the wave structured observed in the field. As such, a preliminary understanding of the formation of recirculating cores in ISWs, the driver for subsequent turbulence, mixing, and particle transport in the interior is obtained.

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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