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This paper discusses the long-term temperature variation of the Southern Yellow Sea Cold Water Mass (SYSCWM) and examines those factors that influence the SYSCWM, based on hydrographic datasets of the China National Standard Section and the Korea Oceanographic Data Center. Surface air temperature, meridional wind speed, and sea surface temperature data are used to describe the seasonal changes. Mean temperature of the two centers of the SYSCWM had different long-term trends. The temperature of the center in the west of the SYSCWM was rising whereas that of the center in the east was falling. Mean temperature of the western center was related to warm water intrusion of the Yellow Sea Warm Current, the winter meridional wind, and the winter air temperature. Summer process played a primary role in the cooling trend of temperature in the eastern center. A decreasing trend of salinity in the eastern half of the SYSCWM showed that warm water intrusion from the south might weaken, as could the SYSCWM circulation. Weakened circulation provided less horizontal heat input to the eastern half of the SYSCWM. Less lateral heat input may have led to the decreasing trend in temperature of the eastern center of the SYSCWM. Further, warmer sea surface temperatures and less heat input in the deep layers intensified the thermocline of the eastern SYSCWM. A stronger thermocline had less heat flux input from upper layers to this half of the SYSCWM. Stronger thermocline and weakened heat input can be seen as two main causes of the cooling temperature trend of the eastern center of the SYSCWM.

Current measurements from three moored Acoustic Doppler Current Profilers (ADCPs) and hydrographic measurements from cruises in the Yellow and East China Seas were used to investigate the North Intrusion of the bottom Taiwan Warm Current Inshore Branch (NI-TWCIB) and its response to wind. The vertical structure of the mean current suggests that NI-TWCIB intrudes into the Jiangsu coasts from the bottom. The observed bottom residual currents run continuously northward at 32 ∘ N from June 12 to August 22, 2014. Synoptic-scale variations of the residual currents indicate that the bottom NI-TWCIB is highly influenced by synoptic process such as wind. Significant variations of the paths of NI-TWCIB are observed from salinity data. The intrusion paths are extracted using a horizontal salinity gradient method, and we characterize the paths by defining the eastern boundary, northern boundary and turning point. The monsoon over the Yellow and East China Seas plays an important role in the variations of the paths of the bottom NI-TWCIB. The pressure gradient set up through Ekman transport and surface transport by easterly and northerly winds promotes the offshore movement of the bottom NI-TWCIB, the northward intrusion, and the northward movement of the turning point. The westerly and southerly winds have opposite effects. We propose a regression method to estimate the intrusion path as a function of east–west winds and north–south winds. The regression results prove that the northern boundary of the bottom NI-TWCIB can arrive at approximately 32 ∘ N, which is consistent with ADCP measurements.

This paper discusses the long-term variation in the salinity of the Southern Yellow Sea Cold Water Mass (SYSCWM) and examines factors influencing the SYSCWM based on hydrographic datasets of the China National Standard section and the Korea Oceanographic Data Center. The mean salinity at the center of the SYSCWM showed a decreasing long-term trend. In empirical orthogonal function (EOF) analysis, the second EOF mode showed a similar long-term trend. The mean salinity of the center of the SYSCWM was related to the intrusion of saline water from the Yellow Sea Warm Current (YSWC), the salinity of the source area of the YSWC, the evaporation minus precipitation (E–P) flux, and discharge from the Changjiang River. The decreasing salinity trend to the southwest of Cheju Island produced a freshening trend in the YSWC, resulting in a reduction in the salinity of the SYSCWM. The freshening trends of the water from the northwest Pacific and the South China Sea were seen as the reason for the decreasing salinity trend from the intrusion of water into the Yellow Sea (YS). The freshwater flux influenced the surface salinity and was brought to deep layers by strong mixing in winter. The mean E–P flux signal and Changjiang River discharge signal lagged the first principal component of the SYSCWM by approximately 5 months.