Yongzeng Yang

Three‐dimensional structure of the summertime circulation in the Yellow Sea from a wave‐tide‐circulation coupled model

[1] The three-dimensional structure of the summertime circulation of the Yellow Sea (hereafter YS) is studied by using a prognostic wave-tide-circulation coupled model based on the Princeton Ocean Model (POM) and a surface wave model. The simulated tidal harmonic constants and temperature structure agree with the observations well. The patterns of the simulated salinity generally agree also with the observations. The simulated results show that the horizontal circulation has a three-layer structure: in the surface layer (0–4 m), the prevailing current direction is northeastward; in the upper layer (4–40 m) it is dominated by a basin scale anticlockwise (cyclonic) gyre; in the bottom layer (below 40 m) the water diverges from the center area and there exists a weak southward current along the YS trough. The stream function of the YS shows that the net circulation of the YS is an anticlockwise (cyclonic) one, and the net transport is about 0.1 Sv. Diagnostic analysis of the momentum balance and sensitivity show that the cyclonic circulation in the upper layers is mainly a quasi-geostrophic flow along tidal-induced temperature front, and it is also strengthened by the tide residual currents. The tidal residual current and the compensation for northward surface layer wind transport contribute to the formation of southward flow in the bottom layer. The vertical circulations vary along different sections. A circulation cell is found in the frontal area near the Korean coast, and an upwelling is found along the slope.

The role of surface waves in the ocean mixed layer

Previously,most ocean circulation models have overlooked the role of the surface waves.As a result,these models have produced insufficient vertical mixing,with an under-prediction of the mixing layer(ML)depth and an over-prediction of the sea surface temperature(SST),particularly during the summer season.As the ocean surface layer determines the lower boundary conditions of the atmosphere,this deficiency has severely limited the performance of the coupled ocean-atmospheric models and hence the climate studies.To overcome this shortcoming,a new parameterization for the wave effects in the ML model that will correct this systematic error of insufficient mixing.The new scheme has enabled the mixing layer to deepen,the surface excessive heating to be corrected,and an excellent agreement with observed global climatologic data.The study indicates that the surface waves are essential for ML formation,and that they are the primer drivers of the upper ocean dynamics;therefore,they are critical for climate studies.

The Statistical Theory of Breaking Entrainment Depth and Surface Whitecap Coverage of Real Sea Waves

Some basic statistics for wave breaking have been derived based on the statistical model of real sea waves. The analytic expressions of breaking entrainment depth and surface whitecap coverage involved with both sea wave characteristics and surface wind velocity have been derived on the basis of the whitecap formation model. The concept of the upper envelope for all the whitecap coverage data versus wind speed has been proposed, and it is assumed to correspond to the whitecap coverage in the case of the infinite wind duration and fetch to determine the model constants. The analytic expressions of breaking entrainment depth and whitecap coverage have been compared with the observations in several ways, and consistently favorable agreement can be found for most observations.

Data assimilation of ocean surface waves using Sentinel-1 SAR during typhoon Malakas

Abstract In this study, a data assimilation system is constructed in a third generation ocean surface wave model, MASNUM-WAM, to improve wave simulations. The data assimilation system uses Ensemble Adjustment Kalman Filter (EAKF) method, which is based on dynamic sampling. Difference between 24 h-interval wave parameter fields during the period 7-day before and after assimilation time, is used to construct dynamic ensemble, which is an approximation to background error. Eight experiments are carried out during typhoon Malakas to investigate the impact of different assimilating wave parameters to the simulation errors of significant wave height (SWH). Wave spectrum observations from satellite Sentinel-1 SAR are used for data assimilation. SWH, peak wave period, mean wave direction and wave spectrum are adjusted simultaneously when an observation is available. Results show that the data assimilation system improves the simulation of SWH during typhoon Malakas.

The improved model of estimating global whitecap coverage based on satellite data

The pro and con of whitecap parameterizations and a statistical wave breaking model are discussed. An improved model is derived by combining satellite-based parameterization and the wave breaking model. The appropriate constants for the general wave state are obtained by considering the breaking condition of the wave slope and fitting with the satellite-based parameterization. The result is close to the constants based on the whitecap data from Monahan. Comparing with satellite-based data and the original model’s results, the improved models results are consistent with satellite-based data and previous studies. The global seasonal distributions of the whitecap coverage averaged from 1998 to 2008 are presented. Spatial and seasonal features of the whitecap coverage are analyzed.