The variations of the marine atmospheric boundary layer (MABL) associated with the South China Sea Summer Monsoon were examined using the Global Positioning System (GPS) sounding datasets obtained four times daily during May-June 1998 on board Research Vessels Kexue 1 and Shiyan 3. The MABL height is defined as the height at the lowest level where virtual potential temperature increases by 1 K from the surface. The results indicate that the MABL height decreased over the northern South China Sea (SCS) and remained the same over the southern SCS, as sea surface temperature (SST) fell for the northern and rose for the southern SCS after the monsoon onset. Over the northern SCS, a decrease in both the SST and the surface latent-heat flux after the onset resulted in a reduction of the MABL height as well as a decoupling of MABL from clouds. It was found that MABL height reduction corresponded to rainfall occurrence. Over the southern SCS, a probable reason for the constant increase of SST and surface heat flux was the rainfall and internal atmospheric dynamics.
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.
