Yineng Li

Impacts of nonbreaking wave‐stirring‐induced mixing on the upper ocean thermal structure and typhoon intensity in the South China Sea

To investigate the effect of nonbreaking wave-induced mixing caused by surface wave stirring on the upper ocean thermal structure (UOTS) and the typhoon intensity, a simple nonbreaking wave-stirring-induced mixing parameterization (WMP) scheme is incorporated into a regional coupled atmosphere-ocean model for the South China Sea (SCS), which couples the Princeton Ocean Model (POM) to the Weather Research and Forecasting (WRF) model using the OASIS3 coupler. The results of simulating two selected typhoon cases indicate that the nonbreaking wave-stirring-induced mixing has significant impacts on UOTS and the typhoon intensity, and the incorporation of the simple WMP scheme in the coupled model helps to improve the simulation of UOTS and thus the typhoon intensity. In the case that the typhoon intensity is underestimated by the atmosphere model alone, the improvement of initial UOTS by the ocean model with the WMP included can deepen the initial thermocline depth, reduce the effect of SST cooling, and prevent the typhoon intensity from undesired weakening. In the case that the typhoon intensity is overestimated (with strong winds), including the WMP in the ocean model significantly enhances the total vertical mixing rate in the upper ocean, which in turn enhances the SST cooling and thus reduces the typhoon intensity as desired. The results obtained in this study make a contribution to the ongoing efforts of improving the typhoon intensity forecast using a regional atmosphere-ocean coupled model by worldwide researchers and forecasters, especially for the typhoons in the SCS regions.

Tidal Mixing in the South China Sea: An Estimate Based on the Internal Tide Energetics

AbstractBy taking into account the contributions of both locally and remotely generated internal tides, the tidal mixing in the Luzon Strait (LS) and the South China Sea (SCS) is investigated through internal-tide simulation and energetics analysis. A three-dimensional nonhydrostatic high-resolution model driven by four primary tidal constituents (M2, S2, K1, and O1) is used for the internal-tide simulation. The baroclinic energy budget analysis reveals that the internal tides radiated from the LS are the dominant energy source for the tidal dissipation in the SCS. In the LS, the estimated depth-integrated turbulent kinetic energy dissipation exceeds O(1) W m−2 atop the two subsurface ridges, with a dissipation rate of >O(10−7) W kg−1 and diapycnal diffusivity of ~O(10−2) m2 s−1. In the SCS, the most intense turbulence occurs in the deep-water basin with a dissipation rate of O(10−8–10−6) W kg−1 and diapycnal diffusivity of O(10−3–10−1) m2 s−1 within the ~2000-m water column above the seafloor as well as ...

Recent advances in regional air-sea coupled models

In this paper, we first briefly review the history of air-sea coupled models, and then introduce the current status and recent advances of regional air-sea coupled models. In particular, we discuss the core technical and scientific issues involved in the development of regional coupled models, including the coupling technique, lateral boundary conditions, the coupling with sea waves (ices), and data assimilation. Furthermore, we introduce the application of regional coupled models in numerical simulation and dynamical downscaling. Finally, we discuss the existing problems and future directions in the development of regional air-sea coupled models.

Adaptive observation in the South China Sea using CNOP approach based on a 3‐D ocean circulation model and its adjoint model

This study investigates the effect of adaptive (or targeted) observation on improving the midrange (30 days) forecast skill of ocean state of the South China Sea (SCS). A region associated with the South China Sea Western Boundary Current (SCSWBC) is chosen as the “target” of the adaptive observation. The Conditional Nonlinear Optimal Perturbation (CNOP) approach is applied to a three-dimensional ocean model and its adjoint model for determining the sensitive region. Results show that the initial errors in the sensitive region determined by the CNOP approach have significant impacts on the forecast of ocean state in the target region; thus, reducing these initial errors through adaptive observation can lead to a better 30 day prediction of ocean state in the target region. Our results suggest that implementing adaptive observation is an effective and cost-saving way to improve an ocean models forecast skill over the SCS.

Polymer light-emitting electrochemical cells with the block copolymers containing PEO segments

Abstract Polymer light-emitting electrochemical cells (LECs) were fabricated and characterized with three block copolymers containing PEO segments as the luminescent polymers. The block copolymers are composed of PPV segments with three phenylene vinylene units and PEO segments with three ethylene oxide units. Blue–green light-emission of the LECs was demonstrated with the onset voltage lower than 3 V and EL efficiency of 0.74 cd/A at 2.8 V. The response time of the LECs is approximately 5 s. The transient response and a.c. impedance data indicate that the operating mechanism of the LECs is an electrochemical doping model.

East Hainan upwelling fronts detected by remote sensing and modelled in summer

Using the Belkin and O’Reilly algorithm and high-resolution (1 km) satellite sea surface temperature (SST) and chlorophyll-a (chl-a) data from 2002 to 2011, fronts were detected off the east/northeast coast of Hainan Island, South China Sea. These fronts were mainly produced by upwelling off eastern Hainan Island, through which cold, high-salinity, high-density, and nutrient-rich bottom water was brought to the surface and subsurface and then transported to the northeast of Hainan Island by the along-shore currents. The fronts are anisotropic, with a dominant orientation SSW–NNE. A three-dimensional ocean model forced by the Quick Scatterometer (QuikSCAT) winds was employed to study the three-dimensional structure of these fronts as well as the relationship between the fronts and upwelling or summer monsoon. The results show that the front intensity (cross-frontal gradient) is strongly correlated with the along-shore local winds, and has a strong seasonal and a weak inter-annual variation with a maximum of about 0.5°C km–1 at the subsurface (about 15 m) rather than the surface.

Eulerian and Lagrangian Statistics in the South China Sea as Deduced from Surface Drifters

AbstractEulerian and Lagrangian statistics of the surface flows over the South China Sea (SCS) are investigated based on observations of satellite-tracked Lagrangian drifters of the Surface Velocity Program. Although the dataset contains the most recent observations up to 2011, the spatial and temporal distributions of the data are quite inhomogeneous. The Luzon Strait as well as the northern and western parts of the SCS are heavily sampled by drifters whereas the internal SCS is less sampled. The overall Eulerian mean circulation derived from all drifter observations resembles the wintertime circulations because of the seasonal sampling bias toward wintertime. It is found that the calculation of the diffusivity may be misled by the low-frequency temporal variabilities such as annual cycle, which could be removed using the Gauss–Markov decomposition. In the regions around Luzon Strait, typical values of diffusivity, time scale, and length scale are 3.7–11.9 × 107 cm2 s−1, 0.8–1.9 days, and 16.4–44.4 km, r...

A parabolic model of drag coefficient for storm surge simulation in the South China Sea.

Drag coefficient (Cd) is an essential metric in the calculation of momentum exchange over the air-sea interface and thus has large impacts on the simulation or forecast of the upper ocean state associated with sea surface winds such as storm surges. Generally, Cd is a function of wind speed. However, the exact relationship between Cd and wind speed is still in dispute, and the widely-used formula that is a linear function of wind speed in an ocean model could lead to large bias at high wind speed. Here we establish a parabolic model of Cd based on storm surge observations and simulation in the South China Sea (SCS) through a number of tropical cyclone cases. Simulation of storm surges for independent Tropical cyclones (TCs) cases indicates that the new parabolic model of Cd outperforms traditional linear models.

Does warmer China land attract more super typhoons

Accurate prediction of where and when typhoons (or named hurricanes which form over the North Atlantic Ocean) will make landfall is critical to protecting human lives and properties. Although the traditional method of typhoon track prediction based on the steering flow theory has been proven to be an effective way in most situations, it slipped up in some cases. Our analysis of the long-term Chinese typhoon records reveals that typhoons, especially super typhoons (those with maximum sustained surface winds of greater than 51 ms−1), have a trend to make landfalls toward warmer land in China over the past 50 years (1960–2009). Numerical sensitivity experiments using an advanced atmospheric model further confirm this finding. Our finding suggests an alternative approach to predict the landfall tracks of the most devastating typhoons in the southeastern China.

A Real-Time Regional Forecasting System Established for the South China Sea and Its Performance in the Track Forecasts of Tropical Cyclones during 2011-13

AbstractA real-time regional forecasting system for the South China Sea (SCS), called the Experimental Platform of Marine Environment Forecasting (EPMEF), is introduced in this paper. EPMEF consists of a regional atmosphere model, a regional ocean model, and a wave model, and performs a real-time run four times a day. Output from the Global Forecast System (GFS) from the National Centers for Environmental Prediction (NCEP) is used as the initial and boundary conditions of two nested domains of the atmosphere model, which can exert a constraint on the development of small- and mesoscale atmospheric perturbations through dynamical downscaling. The forecasted winds at 10-m height from the atmosphere model are used to drive the ocean and wave models. As an initial evaluation, a census on the track predictions of 44 tropical cyclones (TCs) during 2011–13 indicates that the performance of EPMEF is very encouraging and comparable to those of other official agencies worldwide. In particular, EPMEF successfully pr...