The Study On The Water Masses, Kuroshio And Water Exchange In The East China Sea

The main physical processes in the East China Sea (ECS) include the evolutions ofwater masses in the ECS, the seasonal variations of the Taiwan Warm Current Water(TWCW) and its sources, the evolution of Kuroshio Volume Transport (KVT) in theECS, as well as the water exchange in the East China Shelf Sea and its seasonalvariations. These processes control the oceanography factors and the transports ofmass and energy in the ECS. Hence, a systematic study of these processes hasimportant scientific significance. Based on numerous historical in-situ data andsimulation data, this paper studied the evolution mechanisms of these critical marineprocesses in the ECS. The seasonal distributions of water masses in the ECS werediscussed using cluster analysis method, and the dynamic and thermodynamicmechanisms that affected these seasonalvariations were also discussed in detail. Onthe basis of water masses analysis, combined with the model results, the seasonalvariations of the volumeof the TWCW and its sources were explored. Using data inrecent50years derived from the Japan Meteorological Agency, the inter-annual andinter-decadal variability characteristics of the KVT in the ECS were analyzed; theinfluences of the meridional wind and Pacific Decadal Oscillation (PDO) on theKuroshio volume transport were also discussed. The Regional Ocean ModelingSystem (ROMS) was used to simulate the circulation structure of the ECS. Themonthly variability characteristics of the water transport, heat transport and salinitytransport through the main sections around the ECS were also analyzed by using themodel results. The main results and conclusions are as follows:(1) The seasonal distributions of water masses in the ECS were obtained by wateranalysis, and the evolution mechanisms of water masses were also discussed. In theECS above a depth of600m, there are eight water masses in summer but only five inwinter. Among these water masses, the Kuroshio Surface Water (KSW), KuroshioIntermediate Water (KIW), ECS Surface Water (ECSSW), Continental Coastal Water(CCW), and Yellow Sea Surface Water (YSSW) exist throughout the year. The Kuroshio Subsurface Water (KSSW), ECS Deep Water (ECSDW) and Yellow SeaBottom Water (YSBW) are all seasonal water masses, occurring from April throughSeptember. The CCW, ECSSW and KSW all have significant seasonal variations,both in their horizontal and vertical extents and in their T-S properties. The wind is thedominant cause of the seasonal variation in spatial extent of the CCW, ECSSW andKSW. It determines the extent of the ZMCC, the strength of the Taiwan Strait Current,and the intrusion of the Kuroshio.In other words, the wind stress, the Kuroshio and itsbranch currents, and coastal currents are all the dynamical factors determining theseasonal variations in the spatial extent of the CCW, the ECSSW and the KSW. Seasurface heat and freshwater fluxes and river runoff might also be important factors inthe seasonal variations of T-S properties of the three water masses.(2) Theseasonal variations of the volumeof the TWCWas well as its origins wereanalyzed. The results indicated that the Taiwan Warm Current Water was dominatewater mass in the East Chia Shelf Sea; the volume of the TWCW exhibitedpronounced seasonal variations, it reach a maximum (13746km3) in winter, secondin summer (13165km3) and spring (12553km3), andminimum (11397km3)in autumn,,respectively. In winter and autumn, the TWCW is mainly coming from shelf intrusionof the Kuroshio northeast of Taiwan; however, in spring and summer, the TWCW canbe divided into two types: Taiwan Warm Current Surface Water (TWCSW) andTaiwan Warm Current Deep Water (TWCDW). The TWCSW is formed by the mixingof the Kuroshio Surface Water from the east of Taiwan with the water coming fromTaiwan Strait, and the TWCDW is completely originated from the KuroshioSubsurface Water East of Taiwan. In warm half year (April-September), the TWCSWcoming from Taiwan Strait are0.62,0.83,1.05,1.67,1.27and1.01Sv（1Sv=10）respectively. Obviously, the warm water from Taiwan Strait make largest contributionto the TWCSW in July (1.67Sv), about56.5%.(3) High inter-annual and inter-decadal variability was identified in the KuroshioVolume Transport. The analysis results showed thatthe frequency distributions ofKVT appeared nearly to obey normal distribution with a range of19-33Sv; themulti-year seasonal average of the KVT through the PN section is24.30Sv.The (25.91) in summer and minimum (24.27) in fall. The spectral analysis resultsindicated that the primary periods of the KVT variations were5.3,24.9and3.6a,respectively.A linear long-term KVT upward trend was identified for the period1956to2005, the seasonal mean, winter and summer volume transports increased8.72Sv、9.86and9.38Sv in this period, respectively. Correlation and composite analysisshowed that meridional wind anomalies over the source area of Kuroshio and theKuroshio area in the East China Sea were responsible for the inter-annual variabilityin the KVT. Additionally, the inter-decadal variability of the KVT was closelyassociated with the PDO.(4) The relatively complete system of the circulation structure in the ECS wasconstructed. The ROMS results were applied to analyze the monthly volume transport,heat transport and salinity transport through the critical sections in the ECS andadjacent regions. Analysis results showed that the water exchanges in the ECSexhibited pronounced seasonal variations, which mainly take place in the TaiwanStrait (TWS), the section east of Taiwan (TWE), the two sections along Ryuku Island(R1and R2), the Tokara Strait (TKRS), the Osumi Strait (OS), the section east ofCheju Island(CE) and Cheju Strait (CS). The annual mean volume transport throughthese sections were1.06Sv,20.49Sv,3.2Sv,-0.67Sv,-20.59Sv,-0.30Sv,-2.37Svand-0.67Sv (Positive means inward). Comparison of these transports (volume, heatand salinity) indicated that these transports in the ECS had similar trends, themaximum flux often appeared in summer (July or August), and the minimum oftenappeared in winter (January or February). The results also showed that the ECS was aheat source (0.172PW,1PW=1015W), it played a critical role in theglobalheatbalances and transports in the atmosphere and ocean.