Yellow Sea Warm Current Research Articles

Effect of the Yellow Sea warm current fronts on the westward shift of the Yellow Sea warm tongue in winter

Based on long-term and high resolution NOAA/NASA AVHRR Pathfinder SST data and applying new indices, the present study gives a quantitative description of the pattern and interannual variation of the westward shift of the warm tongue (WSWT) relative to the bathymetric trough of the Yellow Sea (YS), which was only qualitatively mentioned in the previous works. The thermal fronts associated with the warm tongue are also accurately determined using a newly presented front-detection method. A new mechanism on the WSWT is presented according to the significant physical relations between the WSWT and fronts. The originally northward flowing YS warm current (YSWC) source water is prevented by the front on its northern side (YF-N), which resides in the east-west direction and across the entrance of the YS trough, from advancing further northward along the YS trough. Instead, the warm water is induced to flow westward along the front and connect with the northward flowing compensating flow in the interior YS, forming the entire westward shifted YS warm tongue. Observations confirm the above hypothesis by revealing the fact that when the northern front moves more southward or becomes stronger, the WSWT enhances. The other local dynamics, such as the wind in the YS and the YSWC itself, do not directly influence the WSWT; however, they do modulate it through determining the position and strength of the YF-N.

北黄海秋、冬季浮游动物多样性及年间变化

Zooplankton species diversity was monitored in the Northern Yellow Sea(121°30′—124°00′E、37°30′—40°00′N) in the autumn and winter of 2009.Based on comparisons with historic data 1959 and 1982,the variation of zooplankton diversity was analyzed.The connection between zooplankton diversity and sea currents and global change was also revealed.Zooplankton samples were collected with a plankton net(mesh size 500 μm) in the Northern Yellow Sea(NYS).A total of 28 species belonging to 8 classes(excluding zooplankton larva and juveniles,fish eggs,and fish larvae) were collected.Warm-temperate and eurythermal species constituted the majority of zooplankton in the NYS and only a small number of cold-temperate and subtropical species were found.Based on zooplankton species composition at each station,community classifications were analyzed using CLUSTER analysis and the SIMPROF test(Primer 6.0 software).Three zooplankton communities were distinguished as:the NYS High Salinity Water Community,the NYS Mixed Water Community and the NYS Coastal Water Community. In the autumn and winter of 2009,the warm water species Doliolum denticulatum and Sagitta enflata were observed in the NYS.The average abundance of D.denticulatum was 81.00 ind/m3 and 0.06 ind/m3 in autumn and winter,respectively.The frequency of occurrence was 57.1% in autumn and 7.1% in winter.The average abundance of S.enflata was 0.24 ind/m3 and 0.37 ind/m3 in autumn and winter,respectively.The frequency of occurrence was 14.3% in autumn and 50.0% in winter.Notably,in autumn of 2009,D.denticulatum became one of the dominant zooplankton species in the NYS.In the same season during 1959,the northward distribution limit of these warm water species did not reach the NYS.The northward expansion of these warm water species might reveal the reinforcement of the Yellow Sea Warm Current(YSWC) from the impacts of climate change. Calanus sinicus and S.crassa were the main warm-temperate species and dominated the zooplankton in both seasons measured.In autumn and winter of 2009,the abundance of both C.sinicus and S.crassa was higher than those in the same period of 1959.In autumn,the average abundance of C.sinicus in 2009 was 3.7 times that in 1959 and 5.4 times that in 1982.The maximum abundance of C.sinicus in 2009 was 3.5 times that in 1959 and 1.7 times that in 1982.The abundance of the main warm-temperate species has increased significantly in the NYS over the past 50 years. We hypothesize that climate change is responsible for the northward expansion of warm water species(D.denticulatum and S.enflata) and the increase in abundance of the main warm-temperate species(C.sinicus and S.crassa) in the NYS.The response model of zooplankton to climate change in the NYS(warm-temperate sea) was different from that in the East China Sea(subtropical sea).This research is of scientific interest for studying the response of zooplankton to global climate change.

Tidal hydrodynamics and fine-grained sediment transport on the radial sand ridge system in the southern Yellow Sea

The large radial sand ridge (RSR) system located in the southern Yellow Sea off the Jiangsu coast is characterized by a radial current field and high suspended sediment concentrations (SSCs). Significant rectilinear currents are present over the northern sand ridge area, whereas rotary currents prevail over the southern area, the transition between the two being dominated by a locally generated trapped wave. Observations undertaken in 2006 and 2007 indicate a seasonal pattern in the SSC and associated dynamic characteristics. The results of a calibrated hydrodynamic model show that the M2 tide dominates the RSR area, the maximum tidal amplitude in the core region close to land being approximately 2m. An amphidromic point is located some distance north of the RSR off the abandoned Yellow River mouth (121.686° E, 34.6° N). Specifically, the Eulerian and Lagrangian residual currents flow southward in both summer and winter, whereas the Stokes' drift is directed southward in the north and northward in the south. Moreover, in deep water the Lagrangian residual current is mainly determined by the Eulerian residual current, whereas it is strongly influenced by the Stokes' drift in shallow water. The seasonal variation in the residual current in the southern Yellow Sea is a good indicator for the location of the Yellow Sea Warm Current (YSWC) in both summer and winter. Measurements show that a SSC peak appears off the abandoned Yellow River delta in response to the strong currents and plentiful supply of fine-grained sediment from coastal erosion. Another SSC peak lying close to the North Branch of the Changjiang River mouth is related to the abundant suspended sediment supplied by the river. Seasonal variations in SSC are observed in the study area, maximum average values and widest diffusion from land occurring in winter, this being contrasted by minimum mean values in summer. Sensitivity experiments demonstrate that the main factor influencing the distribution of SSC is the tide, while river discharge, wind, and wave effects are small and very localized. To explain the seasonal variation in SSC, the role of hydrodynamics, initial conditions, and temperature are tested in the model. The results show that the hydrodynamics play a significant role, whereas the initial conditions only have a minor regional influence. Temperature, on the other hand, is also shown to greatly influence the seasonal variation in SSC because of substantial changes in the viscosity of the water and the erosion shear stress. The modeled results are used to calculate sediment fluxes, which are shown to be consistent with the Lagrangian residual current pattern, while wind waves can significantly change the fluxes in winter. Bed elevations change substantially on a monthly time scale. In general, the deep channels are undergoing erosion, while the shallow ridges and coastal tidal flats are accreting, the net sediment transport being directed towards the coastal tidal flat and the Changjiang (Yangtze) River subaqueous delta.

An asymmetric upwind flow, Yellow Sea Warm Current: 2. Arrested topographic waves in response to the northwesterly wind

[1] A warm and salty water mass exists along the Yellow Sea Trough (YST) in winter. This oceanic water mass is distinct from the ambient shelf water and is distributed on the western side of the YST. It has long been reasoned that a Yellow Sea Warm Current (YSWC) must exist. A recent observational study indeed supports the existence of the YSWC and shows that its position moved progressively westward as the warm water intrudes further shoreward toward the northwest. In this paper, we explain mechanisms for sustaining the YSWC and for its westward displacement. The northwesterly monsoonal wind prevails in the winter and is directed against the YSWC. The cross-trough scale is small compared with the spatial scale of monsoonal variation, so one can assume, to the first order, that the wind stress is uniform across the trough. The curl of depth-averaged wind stress has opposite signs on the two sides of the trough. Consequently, two oppositely rotating gyres develop initially and they converge along the trough giving rise to a barotropic upwind flow. But this upwind flow lasts only for a few days as the two gyres evolve and propagate as topographic waves. For a northerly wind, both gyres move westward since the positive (negative) potential vorticity flux on the western (eastern) side of the trough pushes the water toward shore (trough). If the bottom friction is negligible, the steady response becomes a large anticyclonic gyre over the trough and the upwind current is squeezed toward the shore line. In this case, no YSWC is sustained along or near the trough. This runaway warm current can be arrested by a moderate bottom friction. We therefore propose that the YSWC is actually arrested topographic waves in response to local wind stress forcing.

An asymmetric upwind flow, Yellow Sea Warm Current: 1. New observations in the western Yellow Sea

[1] The winter water mass along the Yellow Sea Trough (YST), especially on the western side of the trough, is considerably warmer and saltier than the ambient shelf water mass. This observed tongue-shape hydrographic feature implies the existence of a winter along-trough and onshore current, often referred to as the Yellow Sea Warm Current (YSWC). However, the YSWC has not been confirmed by direct current measurements and therefore skepticism remains regarding its existence. Some studies suggest that the presence of the warm water could be due to frontal instability, eddies, or synoptic scale wind bursts. It is noted that in situ observations used in most previous studies were from the central and eastern sides of the YST even though it is known that the warm water core is more pronounced along the western side. Data from the western side have been scarce. Here we present a set of newly available Chinese observations, including some from a coordinated effort involving three Chinese vessels in the western YST during the 2006–2007 winter. The data show unambiguously the existence of the warm current on the western side of YST. Both the current and hydrography observations indicate a dominant barotropic structure of YSWC. The westward deviation of YSWC axis is particularly obvious to the south of 35°N and is clearly associated with an onshore movement of warm water. To the north of 35°N, the YSWC flows along the bathymetry with slightly downslope movement. We conclude that the barotropic current is mainly responsible for the warm water intrusion, while the Ekman and baroclinic currents play an important but secondary role. These observations help fill an observational gap and establish a more complete view of the YSWC.

Physical processes and their role on the spatial and temporal variability of the spring phytoplankton bloom in the central Yellow Sea

The spatial and temporal variability of the spring phytoplankton bloom (SPB) in the central Yellow Sea is studied, using SeaWiFS surface chlorophyll remote-sensing data, AVHRR sea surface temperatures (SST), QuikSCAT sea surface wind speed (SSW) from 1998 to 2009 and the cruise survey data in 2007 and 2009. The influences of the hydrological conditions on the SPB are significant. (1) The rising SST and low SSW in spring play an important role in the development of the SPB. The SPB in the central Yellow Sea occurs primarily in April (from April 3 to April 24) and at this period the mean SST is generally greater than 10 °C, and 24 h averaged SSW is less than 5.4 m/s. The 99% of the SPB occurs when the SST is 9–14 °C and SSW is 0–7.9 m/s. (2) Specifically, the development of the SPB is from April 4 to April 7 and from April 4 to April 22 in 2007 and 2009 respectively. The longer duration of the SPB in 2009 than that in 2007 is related to the high SST in 2009, which is approximately 2 °C greater than that in 2007, and the weak SSW in 2009, which is much lower than that in 2007, which further indicate that these two factors are critical to the duration of the SPB. (3) The horizontal distribution of surface chlorophyll a in 2007 is found to be greater and located more northward than that in 2009. Comparing the spatial coverage of the SPB, the path of the Yellow Sea warm current, which is warmer and salty, and the location of maximum SST reveals that the spatial coverage of the SPB locates in the warmer temperature (>9 °C) and higher salinity (>33) waters in March and this warm and salty water was much more evident in 2007 than that in 2009 because a stronger warm current of the Yellow Sea in winter. (4) The vertical depths of the maximum chlorophyll layer (MCL) appear at three levels: surface, 10 m and 30 m in 2007, whereas the MCL occurs only at a sub-surface level in 2009 which is related to vertical stability of the water column, i.e., the water is vertically mixed in 2007 while vertically stratified in 2009.

An open‐ocean forcing in the East China and Yellow seas

Recent studies have demonstrated that the annual mean barotropic currents over the East China and Yellow seas (ECYS) are forced primarily by the oceanic circulation in the open‐ocean basin through the Kuroshio Current (KC), the western boundary current of the subtropical gyre in the North Pacific Ocean. The local wind stress forcing plays an important but secondary role. Those previous results were mainly qualitative and from a simple barotropic model forced by a steady wind stress field. They remain to be tested in a more complete 3‐D model with both wind stress and buoyancy fluxes. In addition, the seasonal variability of major ECYS currents may involve different forcing mechanisms than their annually averaged fields do, and this can only be addressed when a seasonally varying forcing is used in the model. In this paper, we will address these issues by using a 3‐D baroclinic model. Our results confirm the finding from the previous studies that the KC is the primary forcing mechanism for major annually mean currents in the ECYS, which include the Taiwan Strait Current, the Tsushima Warm Current, and the Yellow Sea Warm Current (YSWC), etc. However, the local monsoonal forcing plays a prominent role in modulating the seasonal variability of all major currents in the region. A deep northwestward intrusion of the YSWC in winter, for instance, is mainly due to a robustly developed China Coastal Current and Korea Coastal Current, which draw water along the Yellow Sea Trough to feed the southward flows along the west and east coasts of the Yellow Sea.

A subsurface intensity index of the cold eddy in the East China Sea

The Cold Eddy in the East China Sea (CEECS) is located about 150 km southwest of Cheju Island. This region experiences a complex current system under the influences of the Yellow Sea Warm Current (YSWC), the Yellow Sea Coastal Current (YSCC), and the northward Kuroshio residual. To identify the strength of the CEECS, a simple subsurface intensity index is developed. Because the CEECS can be traced by temperature minimum, the intensity index is determined by the difference in sea temperature averaged across cores within and surrounding the region. Based on SODA, the CEECS subsurface intensity index time series can be calculated, with which the inter-annual variation of the CEECS is analyzed.

Erratum to: Observational evidence of the Yellow Sea warm current

Erratum to: Observational evidence of the Yellow Sea warm current

Observational evidence of the Yellow Sea warm current

The Yellow Sea Warm Current (YSWC) is one of the principal currents in the Yellow Sea in winter. Former examinations on current activity in the Yellow Sea have not observed a stable YSWC because of the positioning of current meters. To further understand the YSWC, a research cruise in the southern Yellow Sea was carried out in the winter of 2006/2007. Five moorings with bottom-mounted acoustic Doppler current profilers (ADCP) were deployed on the western side of the central trough of the Yellow Sea. The existence and distributional features of the YSWC were studied by analyzing three ADCP moorings in the path of the YSWC in conjunction with conductivity-temperature-depth (CTD) data over the observed area in the southern Yellow Sea. The results show the following. (1) The upper layer of the YSWC is strongly influenced by winter cold surge; its direction and speed often vary along a south-north axis when strong cold surges arrive from the north. (2) The YSWC near the bottom layer is a stable northwest flowing current with a speed of 4 to 10 cm/s. By combining the analyses of the CTD data, we speculate that the core of the YSWC may lie near the bottom. (3) On a monthly average timescale, the YSWC is stably oriented with northward flow from the sea surface to the sea floor.

Environmental evolution and impact of the Yellow River sediments on deposition in the Bohai Sea during the last deglaciation

Samples of one core in the Bohai Sea mud area (BSMA) were analyzed in grain size, magnetic susceptibility (MS), major minerals, foraminifera, ostracod, stable isotopes, and 14C dating to reconstruct sedimentary environment and impact of the Yellow River sediments on deposition in the Bohai Sea during the last deglaciation. The central Bohai Sea was river mouth or swamp environment before 12.9 ka BP, when sediments with low MS values had high sand content. Appearance of two peat layers at 11.2 and 12.9 ka BP at Core M7-6 showed that seawater had not yet entered the central Bohai Sea, where the limnetic ostracod was frequently existed and foraminifera were hardly seen. Abundance and diversity of foraminifera began to increase sharply, while their oxygen and carbon isotopes became heavier from ∼9.3 ka BP due to seawater entrance into the central Bohai Sea. Related to intrusion of the Yellow Sea Warm Current (YSWC) extension into the central Bohai Sea, oxygen and carbon isotopes reached the maximum at ∼6.5 ka BP. MS values between 2.4 and 8.3 ka BP increased continually together with slow sedimentation rate, revealing that the impact of the Yellow River sediments was limited because of strong hydrodynamic condition and small sediment discharge. At the last 2.4 ka, the influence of the Yellow River reached the maximum due to large sediment discharge into the Bohai Sea. However, the BSMA had slow sedimentation rate compared with other mud areas in the Chinese marginal seas despite of its close distance from the Yellow River mouth, indicating that although the BSMA was the primary sink of the Yellow River sediments, most of the Yellow River sediments were deposited at other areas (e.g. deltaic areas and Shandong mud wedge).

An N-shape thermal front in the western South Yellow Sea in winter

An N-shape thermal front in the western South Yellow Sea (YS) in winter was detected using Advanced Very High Resolution Radiation (AVHRR) Sea Surface Temperature data and in-situ observations with a merged front-detecting method. The front, which exists from late October through early March, consists of western and eastern wings extending roughly along the northeast-southwest isobaths with a southeastward middle segment across the 20-50 m isobaths. There are north and south inflexions connecting the middle segment with the western and eastern wings, respectively. The middle segment gradually moves southwestward from November through February with its length increasing from 62 km to 107 km and the southern inflexion moving from 36.2A degrees N to 35.3A degrees N. A cold tongue is found to coexist with the N-shape front, and is carried by the coastal jet penetrating southward from the tip of the Shandong Peninsula into the western South YS as revealed by a numerical simulation. After departing from the coast, the jet flows as an anti-cyclonic recirculation below 10 m depth, trapping warmer water originally carried by the compensating Yellow Sea Warm Current (YSWC). A northwestward flowing branch of the YSWC is also found on the lowest level south of the front. The N-shape front initially forms between the cold tongue and warm water involved in the subsurface anti-cyclonical recirculation and extends upwards to the surface through vertical advection and mixing. Correlation analyses reveal that northerly and easterly winds tend to be favorable to the formation and extension of the N-shape front probably through strengthening of the coastal jet and shifting the YSWC pathway eastward, respectively.

The inter-annual variability of the Yellow Sea Warm Current surface axis and its influencing factors

Based on the Pathfinder sea surface temperature (PFSST), the surface axis and its pattern of the Yellow Sea Warm Current (YSWC) are discussed. A structure of double-warm-tongue is found in February and it varies in different years. Two indexes are calculated to represent the westward shift (WSI) and northward extension (NEI) of the warm water in the Yellow Sea (YS). Wavelet analysis illustrates that the WSI and NEI have prominent periods of 3–6 years and 3–4 years, respectively. The Empirical Orthogonal Function (EOF) decomposition is applied to the winter wind stress curl and the Kuroshio Current (KC) transport, which are believed to play important roles in forcing the variability of the YSWC surface axis. Statistics shows that the WSI is significantly related with the second EOF mode of the wind stress curl in February, which may force the YSWC surface axis moving westward and maintaining the double warm tongues because of its opposite curl in the YSWC domain. The first EOF mode of wind stress curl in January is propitious for inducing the warm tongue in the YS to advance more northward. Hence, the wind stress curls both in January and in February could force variations of the YSWC surface axis; however, the effect of the January wind stress curl is relatively weaker than that of the February. The relationship between the NEI and the KC transport is remarkable, and it seems that the stronger KC supplies more power to push the YSWC northward against the southward wind.

Comparison of wind and tidal contributions to seasonal circulation of the Yellow Sea

Seasonal circulation of the Yellow Sea (YS) in response to wind and tidal forces is examined using a three‐dimensional numerical model. Wind forcing affects the wintertime circulation of the YS; on the other hand, the summer southerly monsoon is weak and therefore has little impact on the circulation, on the basis of comparative experiments with and without wind conditions. Results indicate that the Yellow Sea Warm Current (YSWC) along the YS trough exists regardless of wind forcing. However, strong winter northerly winds intensify the southward coastal flows along both coasts of the YS, and therefore, the northward intrusion of the YSWC becomes stronger. These flows in the YS are substantially weakened when wind forcing is not applied to the model. In addition to wind‐driven circulation, tide‐induced circulation is also dominant in the YS, particularly in summer. In winter, the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds, while in summer, tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the YS. The southward residual current possibly explains the southward movement of the Yellow Sea Bottom Cold Water as observed in summer. Comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the YS.

Formation and evolution of the modern warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.

The Study of the Yellow Sea Warm Current and Its Seasonal Variability

The Yellow Sea Warm Current (YSWC) penetrates northward along the Yellow Sea Trough, and brings warm and saline water towards the Bohai Sea. The YSWC becomes much less intrusive in summer and is limited mostly in the southern trough, contrasting with a deep winter penetration well into the trough. The seasonal variability of the YSWC has prompted a debate regarding which controls the YSWC and its seasonal variability. In this article, the annual mean and seasonal variability of the YSWC was examined by using a 3-D ocean model together with several experiments. The results show that in the annual mean the YSWC is a compensating current firstly for the southward Korea Coastal Current (KCC), which is mainly caused by the Kuroshio Current (KC). The local wind-stress forcing plays an important but secondary role. However, the local monsoonal forcing plays a prominent role in modulating the seasonal variability. A deep northwestward intrusion of the YSWC in winter, for instance, is mainly due to a robustly developed China Coastal Current (CCC) which draws water along the Yellow Sea trough to feed a southward flow all the way from the Bohai Sea to the Taiwan Strait.

Wintertime meso-scale horizontal distribution of large tintinnids in the southern Yellow Sea

Spatial distribution of some large tintinnid species (nominally > 76 μm) is investigated on samples vertically towed in the southern Yellow Sea in winters of 2001 to 2004. Nine tintinnid species are recorded: Codonellopsis morchella, Stenosemella pacifica, S. steini, Tintinnopsis schotti, T. radix, T. karajacensis, Eutintinnus tenuis, Parafavella sp., Leprotintinnus neriticus, of which C. morchella and T. radix dominated in the warm tongue-shaped zone of the Yellow Sea Warm Current (YSWC), and S. pacifica is the next in abundance. Our study shows that these tintinnids occur repeatedly in certain special distribution patterns.

Sedimentary changes during the Holocene in the Bohai Sea and its paleoenvironmental implication

Samples of two cores, Cores M5-5 and M7-4 in the Bohai Sea were analyzed in isotopes, grain size, heavy minerals, chemical compositions, and 14C dating to reconstruct the sedimentation during the Holocene. Abrupt change in carbon and oxygen stable isotopes was recognized at Core M5-5 at about 6400 a BP, which was likely due to the intrusion of the Yellow Sea Warm Current (YSWC) extension into the Bohai Sea. At Core M7-4, sediments between 5900 and 6600 a BP (150–260 cm depth) became coarse-grained, containing rich garnet, high manganese content, and nil autogenic pyrite, indicating a very dynamic sedimentary event during which the ambience was transformed from reductive to oxidative, and sedimentation boosted. Meanwhile, the YSWC had invaded into the Bohai Sea indicated by rich planktonic foraminifera in this event.

Observation of the seasonal evolution of the Yellow Sea Cold Water Mass in 1996–1998

We use the hydrographic data obtained during the joint survey of the Yellow Sea by the First Institute of Oceanography, China and the Korea Ocean Research and Development Institute, Korea, to quantify the spatial structures and temporal evolution of the southern Yellow Sea Cold Water Mass (YSCWM). It is indicated that the southern YSCWM is a water mass that develops in summer and decays in fall. In winter, due to the intrusion of the Yellow Sea Warm Current (YSWC), the central area (approximately between 34°N and 35°N, 122°E and 124°E) of the Yellow Sea is mainly occupied by relatively high temperature water ( T>10 °C). By contrast, from early summer to fall, under the seasonal thermocline, the central area of Yellow Sea is occupied by cold water ( T<10 °C). In summer, the southern YSCWM has two cold cores. One is formed locally southeast of Shandong Peninsula, and the other one has a tongue-like feature occupying the area approximately between 34°N and 37°N, 123°E and 126°E. The bottom layer temperature anomalies from February to July in the cold tongue region, along with the trajectories of the bottom floaters, suggest that the cold water mass in the northeast region has a displacement from the north to the central area of the Yellow Sea during the summer.

Effects of the Yellow Sea Warm Current on the winter temperature distribution in a numerical model

The temperature distribution and circulation patterns in the Yellow Sea (YS) are examined by using a wave‐tide‐circulation coupled numerical model. This model sufficiently reproduces the variation of the warm tongue structure of the Yellow Sea Warm Current (YSWC) from the double branches flowing along the YS Trough and the western 60 m isobath in January to the single stream along the western temperature front in March. This is observed in both the long‐term monthly climatology and the satellite‐based sea surface temperature images in recent years. Examining the local heat balance in the numerical model during the entire cooling period, it is found that the YSWC has a very important influence on the YS warm tongue structure. Compared with the surface cooling, the influence of the advection is small in the coastal shallow area but large in the deep warm tongue area (up to 50% of the magnitude of heat flux). Although bathymetry is the essential factor which causes the temperature front, the YSWC is the key factor which positions, shapes, and maintains the warm tongue structure. This helps to affirm the existence of the YSWC, at least as a monthly mean flow. However, more high‐resolution current observations in deeper layers west of Cheju Island and the western fork of the YS Trough are needed to confirm the existence of the YSWC and its characteristic timescale in the real YS.