An Examination of Circulation Characteristics in the Luzon Strait and the South China Sea Using High-Resolution Regional Atmosphere-Ocean Coupled Models

Sea surface winds and water transports through the Luzon Strait (LS) are two main factors that force the circulations in the South China Sea (SCS). Typically, a sandwich-like inflow-outflow-inflow structure in the LS and a corresponding three-layer cyclonic-anticyclonic-cyclonic circulation structure in the SCS have been identified. In this study, the impact of model resolution on the simulation of SCS circulations is investigated through examining the circulation features in different resolution coupled models of the Asia-Pacific Regional Coupled Prediction (AP-RCP) system at the Qingdao Pilot National Laboratory for Marine Science and Technology (QNLM). The AP-RCP system of QNLM consists of a 9-km resolution Regional Ocean Model System (ROMS) coupled with a 27-km resolution Weather Forecast and Research (WRF) atmosphere model (9v27) and a 3-km ROMS coupled with a 9-km WRF (3v9). Results show that compared to the 9-km case, the 3-km resolution ocean model can distinctly depict the topography of Bashi Channel and Luzon Trough, thus simulating the deep circulations of the LS more accurately. In addition, with more mesoscale air-sea interactions, the 3v9 model has better simulation of Kuroshio structure and strength as well as upper layer SCS circulations than the 9v27 model. Our results affirm that due to better representation of complex topography at the LS and eddy-current interactions in the Kuroshio area, the enhanced-resolution coupled model can simulate the LS overflow and Kuroshio intrusion more accurately, which may help to improve the simulation and prediction for SCS circulations and mesoscale activities once the observations are sufficient in the future.