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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 %u2014 the vortical mode, which operates on the same scale as internal waves %u2014 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

Estimates of surface waves using subsurface EM-APEX floats under Typhoon Fanapi 2010

Hsu, J.-Y., R.-C. Lien, E.A. D'Asaro, T.B. Sanford, "Estimates of surface waves using subsurface EM-APEX floats under Typhoon Fanapi 2010," J. Atmos. Ocean. Technol., 35, 1053-1075, doi:10.1175/JTECH-D-17-0121.1, 2018.

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1 May 2018

Seven subsurface Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats measured the voltage induced by the motional induction of seawater under Typhoon Fanapi in 2010. Measurements were processed to estimate high-frequency oceanic velocity variance associated with surface waves. Surface wave peak frequency fp and significant wave height Hs are estimated by a nonlinear least squares fitting to oceanic velocity, assuming a broadband JONSWAP surface wave spectrum. The Hs is further corrected for the effects of float rotation, Earth's geomagnetic field inclination, and surface wave propagation direction. The fp is 0.08–0.10 Hz, with the maximum fp of 0.10 Hz in the rear-left quadrant of Fanapi, which is ~0.02 Hz higher than in the rear-right quadrant. The Hs is 6–12 m, with the maximum in the rear sector of Fanapi. Comparing the estimated fp and Hs with those assuming a single dominant surface wave yields differences of more than 0.02 Hz and 4 m, respectively. The surface waves under Fanapi simulated in the WAVEWATCH III (ww3) model are used to assess and compare to float estimates. Differences in the surface wave spectra of JONSWAP and ww3 yield uncertainties of <5% outside Fanapi’s eyewall and >10% within the eyewall. The estimated fp is 10% less than the simulated ww3 peak wave frequencey before the passage of Fanapi’s eye and 20% less after eye passage. Most differences between Hs and simulated ww3 significant wave height are <2 m except those in the rear-left quadrant of Fanapi, which are ~5 m. Surface wave estimates are important for guiding future model studies of tropical cyclone wave–ocean interactions.

Turbulent mixing within the Kuroshio in the Tokara Strait

Tsutsumi, E., T. Matsuno, R-C. Lien, H. Nakamura, T. Senjyu, and X. Guo, "Turbulent mixing within the Kuroshio in the Tokara Strait," J. Geophys. Res., 122, 7082-7094, doi:10.1002/2017JC013049, 2017.

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4 Sep 2017

Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ~ O(10-3)–O(10-2) m2 s-1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10-1) m2 s-1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10-3) m2 s-1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.

Estimates of surface wind stress and drag coefficients in Typhoon Megi

Hsu, J.-Y., R.-C. Lien, E.A. D'Asaro, and T.B. Sanford, "Estimates of surface wind stress and drag coefficients in Typhoon Megi," J. Phys. Oceanogr., 47, 545-565, doi:10.1175/JPO-D-16-0069.1, 2017.

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1 Mar 2017

Estimates of drag coefficients beneath Typhoon Megi (2010) are calculated from roughly hourly velocity profiles of three EM-APEX floats, air launched ahead of the storm, and from air-deployed dropsondes measurements and microwave estimates of the 10-m wind field. The profiles are corrected to minimize contributions from tides and low-frequency motions and thus isolate the current induced by Typhoon Megi. Surface wind stress is computed from the linear momentum budget in the upper 150 m. Three-dimensional numerical simulations of the oceanic response to Typhoon Megi indicate that with small corrections, the linear momentum budget is accurate to 15% before the passage of the eye but cannot be applied reliably thereafter. Monte Carlo error estimates indicate that stress estimates can be made for wind speeds greater than 25 m s-1; the error decreases with greater wind speeds. Downwind and crosswind drag coefficients are computed from the computed stress and the mapped wind data. Downwind drag coefficients increase to 3.5 ± 0.7 x 10-3 at 31 m s-1, a value greater than most previous estimates, but decrease to 2.0 ± 0.4 x 10-3 for wind speeds > 45 m s-1, in agreement with previous estimates. The crosswind drag coefficient of 1.6 ± 0.5 x 10-3 at wind speeds 30–45 m s-1 implies that the wind stress is about 20° clockwise from the 10-m wind vector and thus not directly downwind, as is often assumed.

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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