The observed variations of the north intrusion of the bottom Taiwan Warm Current Inshore Branch and its response to wind

Abstract

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.