A Fine Grid Tide-Wave-Ocean Circulation Coupled Model for the Yellow Sea: Comparison of Turbulence Closure Schemes in Reproducing Temperature Distributions

The performance of three turbulence closure schemes (TCSs), the generic length scale scheme (GLS), the Mellor–Yamada 2.5 scheme (MY2.5) and the K-profile parameterization scheme (KPP), embedded in the ocean model ROMS, was compared with attention to the reproduction of summertime temperature distribution in the Yellow Sea. The ROMS model has a horizontal resolution of 1/30° and 30 vertical sigma layers. For model validation, root mean square errors were checked, comparing model results with wave and temperature buoy data as well as tidal station data supplied by various organizations within the Republic of Korea. Computed temperature and vertical temperature diffusion coefficients were mainly compared along Lines A (36° N) and B (125° E) crossing the central Yellow Sea, Lines C (32° N) and E (34° N) passing over the Yangtze Bank and Line D off the Taean Peninsula. Calculations showed that GLS and MY2.5 produced vertical mixing stronger than KPP in both the surface and bottom layers, but the overall results were reasonably close to each other. The lack of observational data was a hindrance in comparing the detailed performance between the TCSs. However, it was noted that the simulation capability of cold patches in the tidal mixing front can be useful in identifying the better performing turbulence closure scheme. GLS and MY2.5 clearly produced the cold patch located near the western end of Line E (122° E–122.3° E), while KPP hardly produced its presence. Similar results were obtained along Line D but with a less pronounced tidal mixing front. Along Line C, GLS and MY2.5 produced a cold patch on the western slope of the Yellow Sea, the presence of which had never been reported. Additional measurements near 125° E–126° E of Line C and along the channel off the Taean Peninsula (Line D) are recommended to ensure the relative performance superiority between the TCSs.

7. Tidal mixing

‘Tidal mixing’ describes tidal mixing in shelf seas, where the water is shallow and tidal currents can be much faster than in the deep ocean. Most of the energy lost from the tide through friction is first converted into turbulence, which then makes a very effective mixing mechanism, stirring the Sun’s heat downwards. Shelf seas at temperate latitudes in summer are divided into stratified regions and vertically mixed regions, depending on the tidal streams’ strength and the water depth. The transition from one to the other happens rapidly and creates a tidal mixing front. Tidal mixing in estuaries is also discussed along with the harnessing of tides to generate electricity.

The effects of a tidal-mixing front on the distribution of larval fish habitats in a semi-enclosed sea during winter

We examined the effect of a tidal-mixing front on the three-dimensional distribution of larval fish habitats (LFHs) in the Midriff Archipelago Region in the Gulf of California during winter. Zooplankton and environmental variables were sampled from 0 to 200 m in 50 m strata. Four LFHs were defined in association with the front, two on the northern side and two on the southern side. The northern LFHs were: (1) the Mainland Shelf Habitat, located from the surface to 100 m depth on the north-east mainland shelf, characterized mainly by the presence of Citharichtys fragilis; and (2) the Wide Distribution Habitat, extending from north-west to south across the front from the surface to 200 m depth, dominated by the ubiquitous Engraulis mordax. The southern LFHs were: (3) the Eddy Zone Habitat, defined nearly on an anticyclonic eddy, with the highest larval abundance and richness from the surface to 100 m depth, dominated by Leuroglossus stilbius; and (4) the Southern Gulf Habitat, associated with low temperature waters from the southern Gulf of California, dominated by southern-gulf species (e.g. Scomber japonicus and Sardinops sagax). Despite the weak stratification and low thermal contrast (~1.5°C) across the south front compared to summer (~3°C), our results demonstrate that the frontal zone may influence the formation of planktonic habitats even during generally homogeneous periods, which may also be relevant in other regions of the world.