Diurnal evolution of the barrier layer (BL) and its local feedback features in the central Taiwan Strait (119.2oE,24.3oN) during summertime monsoon are investigated using in situ moored observations conducted by the "Yan-Ping 2" research vessel in late June 2005.During the initiation phase,for the non-solar radiation tends to be trapped in the upper mixed layer,whereas the solar radiation can penetrate deeply through the mixed layer approaching the thermocline,most heat is accumulated inside the BL inducing an inverse-thermal layer.Along with heat convergence inside the BL,thermal exchange increases between the BL and the overlaying mixed layer and finally,a prominently warming mixed layer is formed.Moreover,the BL is associated with a buoyancy frequency minimum with mild stability.Further analysis reveals that the BL's local feedbacks can be divided into two aspects,on one hand,the BL can generate dramatic changes in the local sensible and latent heat fluxes;on the other hand,the sub-halocline and the thermocline serve as two interfaces during the downward transmission of the wind stirring turbulent kinetic energy (TKE) and as a result,most TKE is retarded by the shallow halocline and being trapped above the upper mixed layer,while the residual pierced through the base of the mixed layer is likewise blocked by the thermocline.
PAN AiJun1,WAN XiaoFang,CHEN HangYu & GUO XiaoGang Ocean Dynamics Lab.,Third Institute of Oceanography State Oceanic Administration (TIOSOA),Xiamen 361005,China
In conjunction with synchronous remotely sensed winds and sea surface temperature(SST),the spatiotemporal features of the Zhe-Min coastal current(ZMCC),especially responses of the ZMCC adjacent to Pingtan Island(PT) to the wintertime monsoon relaxation in 2006 and corresponding mechanism are investigated based on the field observations.In situ data are acquired from Conductivity-Temperature-Depth(CTD) cruise and Bottom-Mounted Moorings(BMM),which are conducted during a comprehensive survey for the Chinese Offshore Investigation and Assessment Project in winter 2006.It is revealed that the ZMCC is well mixed vertically in winter 2006.The ZMCC(<14°C) recedes during the relaxation of the wintertime monsoon and is accompanied by the enhanced northward shift of the warm,saline Taiwan Strait Mixed Water(TSMW,higher than 14°C and is constituted by the Taiwan Strait Warm Water and the Kuroshio Branch Water).And greatly enhanced southward intrusion of the ZMCC can be detected when the wintertime monsoon restores.Correspondingly,the thermal interface bounded by the ZMCC and the TSMW moves in the northwest/southeast direction,leading to periodic warm/cold reversals of the near-seabed temperature adjacent to the PT.By EOF(Empirical Orthogonal Function) analysis of the large-scale wind fields and wavelet power spectrum analysis of the water level,ocean current and the near-seabed temperature,responses of the ZMCC off the PT to wintertime monsoon relaxation are suggested to be attributed mainly to the southward propagating coastally trapped waves triggered by the impeding atmospheric fronts.As a result,ocean current and near-seabed temperature demonstrate significant quasi-5 d and quasi-10 d subtidal oscillations.By contrast,the onshore/offshore water accumulation resulted from Ekman advection driven by the local winds has minor contributions.
