Yellow And East China Seas Research Articles

Rapid merger and recyclogenesis of twin extratropical cyclones leading to heavy precipitation around Japan on 9–10 October 2001

AbstractThe significance of twin extratropical cyclones (in contrast to twin tropical cyclones) has not yet been fully recognized in weather forecasting and analysis of heavy precipitation. This study investigated successive sets of twin extratropical cyclones over the Yellow and East China Seas (YECS) and over the Japan Sea and South Coast areas of the Japanese Islands (JSSC) on 9–10 October 2001. Although these twin cyclones were not strong, they led to heavy precipitation in Japan. The southern low of the YECS twin cyclones, which accompanied a moist tongue, rapidly merged with the northern cold low, resulting in the formation of a moist tongue across the Japanese Islands, causing heavy precipitation. This rapid merger is explained by a coupling of cold upper‐ and warm lower‐level lows in a contact binary rotation system. Subsequently, the JSSC twin cyclones became newly organized. The northern deep low of the JSSC twin cyclones formed north of an upper‐level jet by the merger of the YECS cyclones, while the southern shallow low newly formed around the occlusion point south of the upper‐level jet. The sensitivity experiments of successive sets of the twin cyclones show that condensational heating and topographic effects contribute to the formation of the twin structures. The northern low of the JSSC twin cyclones is amplified by latent heating, while the southern low is hardly amplified. The topography of the Japanese Islands results in intensification of the upward flow and cyclonical flow via topographic convergence and blocking of horizontal flow. Copyright © 2011 Royal Meteorological Society

An improved method for evaluating the seasonal variability of total suspended sediment flux field in the Yellow and East China Seas

The suspended sediment flux field in the Yellow and East China Seas (YECS) displays its seasonal variability. A new method is introduced in this paper to obtain the flux field via retrieval of ocean color remote sensing data, statistical analysis of historical suspended sediment concentration data, and numerical simulation of three-dimensional (3D) flow velocity. The components of the sediment flux field include (i) surface suspended sediment concentration inverted from ocean color remote sensing data; (ii) vertical distribution of suspended sediment concentration obtained by statistical analysis of historical observation data; and (iii) 3D flow field modeled by a numerical simulation. With the improved method, the 3D suspended sediment flux field in the YECS has been illustrated. By comparison with the suspended sediment flux field solely based on the numerical simulation of a suspended sediment transport model, the suspended sediment flux field obtained by the improved method is found to be more reliable. The 3D suspended sediment flux field from ocean colour remote sensing and in situ observation are more closer to the reality. Furthermore, by quantitatively analyzing the newly obtained suspended sediment flux field, the quantity of sediment erosion and deposition within the different regions can be evaluated. The sediment exchange between the Yellow Sea and the East China Sea can be evident. The mechanism of suspended sediment transport in the YECS can be better understood. In particular, it is suggested that the long-term transport of suspended sediment is controlled mainly by the circulation pattern, especially the current in winter.

Effects of the Changjiang river discharge on sea surface warming in the Yellow and East China Seas in summer

This study explores the effects of the Changjiang (also called the Yangtze River) river discharge (CRD) on the density stratifications and associated sea surface temperature (SST) changes using a global ocean general circulation model with regional focus on the Yellow and East China Seas (YECS). It is found that CRD increases the SST in summer through a barrier layer (BL) formation that tends to enhance stratification at the mixed layer base, and thus reduces both vertical mixing and entrainment. This process is effective, particularly in August, after the CRD reaches its maximum in July. The SST difference between the composites of flood and drought years confirms that the surface warming is related to surface freshening by the CRD. This result suggests that the BL induced by the CRD is an important contributor to the surface heat budget in the YECS.

Mesoscale air-sea interaction during the passage of a typhoon over the Yellow and East China Seas

In order to best capture the mutual forcing and feedback process to improve the accuracy of modeling of the mesoscale process, we developed the two-way coupling model MCM (Mesoscale Coupled Model) based on two independent models, the atmospheric model MM5v3 and the ocean model ECOM-si, using a flux coupler designed with the concurrent process communication technique. We selected Typhoon Winnie (9711) passing over the Yellow and East China Seas (YECS) to test the performance of the coupling model, and analyzed the quantitative impacts on atmospheric and oceanic variations. The results show that the simulated air-sea heat and momentum exchanges strongly affect circulation in both the atmosphere and the ocean. When mesoscale air-sea interaction is considered, the results for the atmosphere and ocean improved considerably. In terms of atmosphere, the air-sea interaction updates the distribution of elements (e.g., wind, heat flux, relative humidity and temperature) in the vertical and horizontal fields. The forecast result of typhoon intensity becomes more realistic, with decreases in central pressure error of 3.4 hPa at 30 hr and 9 hPa at 60 hr. A strong wind drives the cyclonic ocean current in the upper layer and induces horizontal transport and vertical mixing. All of these processes directly influence the Sea Surface Temperature (SST), which decreases over a large area, particularly near the typhoon center, and can reach 5°C. Finally, we discuss a possible negative feedback mechanism.

Sea-surface temperature fronts in the Yellow and East China Seas from TRMM microwave imager data

Abstract Swath data from the Tropical Rainfall Measuring Mission microwave imager of sea-surface temperatures (SST) from 1998 to 2005 have been used to analyze the climatology and seasonal variability of the SST fronts in the Yellow and East China Seas (YES). Seven fronts have been identified and placed into three categories, namely, (1) the shelf-break front (Kuroshio Front), (2) the coastal fronts (Zhe-Min, Jiangsu, Shangdong Peninsula, Western Korean, and Western Chejudo Fronts), and (3) the shelf front (Western Yellow Sea Shelf Front). The Kuroshio Front exists from December through May, with the maximum SST gradient and highest frontal probability in April. The five coastal fronts exist year-round, all with their maximum SST gradient and highest frontal probability in February. The shelf front in the western Yellow Sea exists only from January to March. Frontogenesis in winter is due to effects of both air–sea heat exchange and advection by currents. The coastal fronts in the stratified months are expressed as tidal fronts. The coastal frontal zones coincide with the major spawning grounds of fish in the YES. The overwintering fishery ground in the Yellow Sea overlaps with the narrow band of favorable water temperature in the frontal zone. The overwintering grounds in the East China Sea are broad and bounded by fronts.

Influences of the surface wave-induced mixing and tidal mixing on the vertical temperature structure of the Yellow and East China Seas in summer*

Abstract After a classification of the physical processes which affect the vertical mixing, diffusivity induced by the surface wave momentum and tidal currents and its influence on the vertical temperature structure are discussed. Based on three mixing schemes' the vertical temperature structure of the Yellow and East China Seas (YECS) is simulated. Results show that in summer, the surface wave-induced mixing plays a key role in forming the upper mixed layer in the YECS. The tidal mixing controls the lower layers within 30 m above the bottom, which is the main factor in forming the platform-shaped temperature structure in the southern Yellow Sea (YS). Together with the strong surface wave-induced mixing, the tidal mixing makes the thermocline ventilate near the east coast of the southern YS. The double cold cores in the deeper layers of the East Chine Sea have different causes. The western one is the maintenance of the winter cold water, while the eastern one is configured by circulation. The simulated ve...

Yellow and East China Seas response to winds and currents

The influences of the Kuroshio Current (KUC), Taiwan Warm Current (TWC), and surface wind stress on the Yellow and East China Seas (YES) are examined using tracers in a Princeton Ocean Model. Two experiments are performed: one with wind stress and one without. Seasonal variations in the inflow and outflow of the TWC and Tsushima Current are specified to examine the effects of the current transports. Two separate tracers are inserted into each model experiment to track the pattern of KUC and TWC waters into the YES. The two main areas of KUC and TWC water movement into the Yellow Sea are the southern entrance to the Yellow Sea trough and the Yangtze Relict River valley. Results indicate that KUC and TWC waters advect into the Yellow Sea regardless of wind stress. However, in the Yellow Sea during winter the wind stress increases KUC and TWC concentration at 20 m. The wind stress also produces short time period events that horizontally advect water masses and spatially smooth seasonally averaged water mass concentrations. The bottom Ekman layer appears to be one of the mechanisms driving the northward bottom flow across the East China Sea shelf. The bottom friction layer is stronger in summer when the TWC velocity is high. The bottom friction layer draws KUC water across the bottom of the continental shelf into the Yangtze Relict River valley and generates upwelling along the Chinese coast.

Fine grid tidal modeling of the Yellow and East China Seas

A fine grid tidal modeling experiment is carried out in order to investigate the tidal regimes for major five tidal constituents, the nonlinear tidal phenomena in terms of M 4 and MS 4 generation, and the independent tide by the tide generating force in the Yellow and East China Seas (YECS). In this study a two-dimensional numerical model based upon a subgrid-scale (SGS) stress modeling technique is used with the tide generating force included. The model was validated with recently observed tide and current data. The calculated tidal charts for tidal elevation show a generally good agreement with existing ones, with more accurate feature of the M 2 cotidal chart in comparison with both the observed data and the existing tidal charts. A careful comparison of the computed diurnal amplitude with observations suggests that the diurnal constituents seem to be overdamped especially in the Kyunggi Bay region, for the case when quadratic bottom friction law is used. Propagation features of the M 4( MS 4) tides are discussed in the YECS, based upon the analyses of the observed and calculated results. The amphidromic system of the M 4 is quite complicated and one noticeable characteristic is that the propagation direction of the M 4 tidal wave along the west coast of Korean peninsula is opposite to that of the M 2 tidal wave. This result coincides with observations. The propagation feature of the MS 4 is almost similar to that of the M 4, but with lesser amplitude. The responses of the M 4 tidal features to momentum diffusion term and depth-dependent form of the friction coefficient are also discussed. It is also shown that when the independent tide ( Defant, 1960) arising from tide generating force (TGF) coexists with tidal waves (co-oscillating tide) arising from external boundary forcing, the TGF tidal waves are dissipated and their amphidromes tend to move westward. This may be interpreted as a process whereby the incident and reflected TGF tidal waves are damped by co-oscillating tide arising from external force at open boundaries. The TGF amplitude is found to be up to 10 cm and 4 cm in the Kyunggi Bay for the M 2 and S 2 constituents while those for all diurnal constituents are less than 1 cm over the entire model domain.

Comparison of winter and summer hydrographic observations in the Yellow and East China Seas and adjacent Kuroshio during 1986

Two regional hydrographic surveys conducted in January and July 1986, aboard the R.V. Thompson and R.V. Washington illustrate the seasonal change in water properties from winter to summer in the Yellow and East China Seas (YECS) and adjacent Kuroshio. In January 1986, water over the shelf in the YECS was locally well mixed in the vertical, and the horizontal distribution of water properties was dominated by a large tongue or plume of relatively fresh Yellow Sea Cold Water (YSCW) flowing southeastward along the Chinese margin into the East China Sea. To the east of this plume, along the Korean margin, was found the more saline Yellow Sea Warm Water (YSWW). The Kuroshio front in the East China Sea was located at the shelf break, separating the warmer, more saline Kuroshio water from the relatively well-mixed cooler, less saline coastal water. Evidence of mixing between these two water masses was observed but limited to near the shelf break. In July 1986, water over the shelf in the YECS was strongly stratified everywhere except within tidally mixed areas near the coast. The surface water distribution in the YECS was dominated by a bubble or lens of Changjiang dilute water located to the northeast of the Changjiang mouth, and the bottom YSCW intensified and extended southward to the shelf break. The relatively fresh coastal water from the East China Sea shelf extended far past the shelf break over the Kuroshio near the surface, and in turn, Kuroshio water intruded onto the shelf near the bottom. Mixing between the Kuroshio and coastal water was found over much of the mid- and outer shelf and upper slope, spanning a cross-stream distance of 75 km. The seasonal freshening due to the Changjiang discharge contributed directly to the summer increase in freshwater transport in the upper Kuroshio. In addition, evidence of deep vertical mixing within the Kuroshio itself was found near 32.0°N, 128.2°E, most likely due to a mesoscale eddy found near there and internal tidal mixing over the slope.