| Abstract: | During the northeast monsoon season, Zhe-Min Coastal Current (ZMCC) travels along the Chinese mainlandcoast and carries fresh, cold, and eutrophic water. ZMCC is significantly important for the hydrodynamic processes and marine ecosystems along its path. Thus, this bottom-trapped plume deserves to be further discussed in terms of the major driving factor, for which different opinions exist. For this purpose, in this study, a high resolution Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) is established and validated. High correlation coefficients exist between along-shelf wind speeds and seasonal variations of both ZMCC volume transport and the freshwater signal. These coefficients imply that the wind is important in regulating ZMCC. However, for similar annual mean ZMCC volume transports, the extreme south boundaries of Zhe-Min Coastal Water (ZMCW) are different among different years. This difference is attracting attention and is explored in this study. According to the low wind/discharge experiment, it was found that although the volume transport of ZMCC is more sensitive to the variation of local wind speeds, the carried freshwater is limited by the Changjiang River discharge, which ultimately determines the south boundary of ZMCW. The momentum analysis at transects I and Ⅱ shows that, for driving ZMCC, the along-shore wind forcing is as important as the buoyancy forcing. Note that this conclusion is supported by a zero-discharge experiment. It was also found that the buoyancy forcing varies with respect to time and space, which is due to variations of the discharge of Changjiang River. In addition, a particle tracking experiment shows that the substance carried by the Changjiang River diluted water would distribute along the Zhe-Min coastal region during the northeast monsoon season and it may escape due to the wind relaxation. |
