Program

Both regional and global ocean models have been widely used to study the three-dimensional circulation in the marginal South China Sea (SCS), which is driven extrinsically by water exchange with Pacific Ocean through Luzon Strait, and intrinsically by the relevant local dynamic response. While global models tended to ‘smoothly’ link the remote forcing of the water exchanges with the local one in one computation domain, they often failed to capture realistic SCS circulation, mainly due to their poor simulations of both remote and local forcing for the regional circulation. This research validated and compared the long-term (1993-2012) simulations from our regional model, CMOMS (China Sea Multi-scale Ocean Modeling System, Gan et al., 2016), and the well-known global models, HYCOM (Hybrid Coordinate Ocean Model) and OFES (OGCM for the Earth Simulator) in resolving the spatiotemporal varying circulations in the SCS. All these three models have similar numerical and physical implementations. The long-term averages of hydrographic properties from WOA13 (World Ocean Atlas, 2013) and GDEM (Global Digital Elevation Model) are adapted as observational references. It is found that both HYCOM and OFES didn’t well simulate the spatiotemporal variation of the observed hydrographic properties in the SCS basin, while these properties were well captured by CMOMS. This was mainly caused by the failure of these global models in resolving the observed intrusion-extrusion-intrusion transports in the upper (0-750 m), intermediate (750-1500 m) and deep (1500 m - bottom) layers in Luzon Strait. Consequently, they failed to capture the observed three-layer, alternative cyclonic-anticyclonic-cyclonic (CAC) circulation in the SCS, since the CAC circulation was dynamically rationalized to be driven by planetary vorticity flux provided by the three-layer intrusion-extrusion-intrusion transport in Luzon Strait. The dynamic inconsistency imposed by strong constrain of data assimilation in HYCOM and incorrect linkage of remote and local forcing in the entire East Asia Marginal Seas in OFES are also believed to be the error sources for the failure in resolving the spatiotemporal structures of the circulation in the SCS.