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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

Turbulent mixing on sloping bottom of an energetic tidal channel

H.-J. Shao, R.-S. Tseng, R.-C. Lien, Y.-C. Chang, J.-M. Chen, "Turbulent mixing on sloping bottom of an energetic tidal channel," Cont. Shelf Res., 166, 44-53, doi:10.1016/j.csr.2018.06.012, 2018.

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1 Aug 2018

Measurements of turbulence dissipation, current, and stratification in an energetic, sloping tidal channel, the Penghu Channel (PHC), in the Taiwan Strait were conducted to investigate temporal variations of turbulence properties in the bottom boundary layer (BBL) under different stratified conditions. It was found that the PHC exhibits a unique feature of semidiurnal cycle of turbulence in the BBL due to the fact that current speeds during the flood are much higher than those during the ebb. Turbulent mixing in the BBL, produced mainly by the tidal current shear, has high values of dissipation (~10-5 W Kg-1) and eddy diffusivity and extends upward to approximately 40  m above the bottom during the flood. During the flood upslope flow, significant temperature drop and destratification of the near-bottom layer occur due to turbulence mixing associated with the shear instabilities, confirmed by the gradient Richardson number less than the critical value of 1/4. By contrast, stratification produced during the ebb is discernible only in the upper part of the BBL above the mixed layer. The stratification is weak (strong) during enhanced (suppressed) turbulence. The observed dissipation rate of turbulent kinetic energy is proportional to the cubic power of current speed, suggesting that the observed turbulence is generated via the boundary layer shear instability.

Upper ocean response to the atmospheric cold pools associated with the Madden–Julian oscillation

Pei, S., T. Shinoda, A. Soloviev, and R.-C. Lien, "Upper ocean response to the atmospheric cold pools associated with the Madden–Julian oscillation," Geophys. Res. Lett., 45, 5020-5029, doi:10.1029/2018GL077825, 2018.

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28 May 2018

Atmospheric cold pools are frequently observed during the Madden–Julian Oscillation events and play an important role in the development and organization of large‐scale convection. They are generally associated with heavy precipitation and strong winds, inducing large air‐sea fluxes and significant sea surface temperature (SST) fluctuations. This study provides a first detailed investigation of the upper ocean response to the strong cold pools associated with the Madden–Julian Oscillation, based on the analysis of in situ data collected during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign and one‐dimensional ocean model simulations validated by the data. During strong cold pools, SST drops rapidly due to the atmospheric cooling in a shoaled mixed layer caused by the enhanced near‐surface salinity stratification generated by heavy precipitation. Significant contribution also comes from the component of surface heat flux produced by the cold rain temperature. After the period of heavy rain, while net surface cooling remains, SST gradually recovers due to the enhanced entrainment of warmer waters below the mixed layer.

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.

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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