In this study the mesoscale and submesoscale features in the South China Sea (SCS) are characterized based on a submesoscale-permitting numerical simulation (MITgcm llc4320) with nominal horizontal grid spacing of 1/48^o (~2.2 km in the SCS). The simulation includes tidal forcing, which is particularly crucial in the SCS where tides play a key role in many aspects of regional dynamics. Evaluation against observations demonstrates that the simulation is capable of reproducing a wide spectrum of dynamical features in the SCS. The simulation is then used to characterize meso- to submesoscale features in the SCS and the key findings are summarized as follows: (i) the SCS is rich in submesoscale features (e.g., vortices, filaments), which undergo significant seasonal variations in many regions; (ii) there is a clear dominance of positive surface relative vorticity () in most regions of the SCS presumably due to the centrifugal instability, but large negative also emerges in areas with strong flow-topography interactions; (iii) the vertical motions in the upper SCS are dominated by tidal modulations with strong vertical velocities up to 0.01 m s^?1, about an order of magnitude larger than those due to the quasi-balanced sub-inertial motions; and (iv) both the wintertime and summertime horizontal wavenumber spectra of kinetic energy scale roughly as k^?2 (with k being the horizontal wavenumber) for wavelengths below 100 km. In addition, four key regions are highlighted with distinctive characteristics of submesoscale turbulence, including the northern SCS, Luzon Strait, the SCS western boundary current region in winter, and east of Vietnam in summer. A number of model deficiencies are noted, along with suggestions for improving model accuracy in order to better characterize the local submesoscale features as well as the underlying dynamics.

南海中尺度至亚中尺度的特征研究

中文摘要：本文基于标准水平网格间距为1/48^o (南海约2.2 km)的亚中尺度数值模拟（MITgcm llc4320）对南海中尺度和亚中尺度特征进行了研究。该模式包含在南海区域动力学的许多方面起着关键作用的潮汐强迫。观测结果的评估表明该模拟能够重现南海的广泛的动力特征。利用该模式研究南海中尺度至亚中尺度特征，主要发现如下:(i)南海具有丰富的亚中尺度特征(如涡旋、涡丝等)且在多个区域具有明显的季节变化特征;(ii)南海大部分区域可能在离心不稳定的作用下表现为正海面相对涡度（），但海面相对涡度在流-地形相互作用较强的区域为较大的负值；(iii)南海上层的垂向运动以潮汐调制为主，垂向流度高达0.01 m s^?1相比准平衡亚惯性运动大一个量级;(iv)冬季和夏季波长小于100 km的动能水平波数谱的比例大致为k^?2 (k为水平波数)。此外，南海北部、吕宋海峡、冬季南海西部边界流区和夏季越南东部等4个关键区域具有明显的亚中尺度湍流特征。本文指出了该模型存在不足之处并给出了提高模型精确度的建议，以便更好地研究局地亚中尺度特征和潜在的动力过程。