南海盐致障碍层及其对区域海气相互作用的影响

Salinity-induced barrier layer (BL) has important consequences on the air-sea interactions and important potential climatic impact. Furthermore, the warm reservoir below the upper mixed layer associated to a classical BL can potentially be eroded by intense atmospheric forcing and thus induce a positive sea surface temperature anomaly that was suggested to significantly influence the development of the monsoon and tropical cyclones..Based on combined observational dataset, WOD01+SCSIO+ARGO, the collection of 17,898 instantaneous temperature and salinity profiles, climatology of monthly mean properties of the BL phenomenon and its potential climatic impact in the South China Sea (SCS) are constructed in this study. This climatology is based on the individual analysis of instantaneous profiles in contrast with previous large-scale climatologies derived from gridded fields. A variety of satellite measurements and high resolution model output in addition to the observation datasets are also used to illustrate kinematics of barrier layer formation and growth processes. Several mainly types of BL are focused in this study, the barrier layer formed when a vertically sheared horizontal flow advects a horizontal salinity gradient, the barrier layer formed when vertical advection acting uniformly on both the halocline and the thermocline, the barrier layer can grow through when vertical stretching vertical velocity acts nonuniformly on the two depth surfaces; and barrier layer formed during rainfall, in the absence of strong turbulent mixing and surface heating. The point is to use a dataset as accurate as possible to test the robustness of the features detected in previous studies, to investigate the possible presence of new, unknown BL and to gain understanding on the BL in the SCS.??.In order to test the importance of the BL on the regional air-sea interactions, the control and the perturbed experiments are conducted in the Regional Ocean Modeling System (ROMS). We take advantage of the vertical mixing scheme, in which the dissipation of the density gradient is related to the Brunt-Vaisala frequency used in ROMS. In the perturbed experiments, only temperature profiles in this frequency computation by canceling the coefficients relative to the salinity in the polynomial formulation at all vertical levels. The changes are mainly confined within the upper ocean and the BL is effectively weakened or even eliminated. The possibility that the BL affects the regional air-sea interaction investigated in this study will plead for a careful consideration of the salinity stratification in the air-sea interactions and climate forecasts.

南海的盐致障碍层由于其独特的海气反馈特征，对上层海洋热力结构和环流有重要影响，可能与南海暖水的形成、南海局地异常增暖等密切相关。本申请在明确南海上层盐度的垂向层结和障碍层分布特征的基础上，研究障碍层对海气过程的多时空尺度的响应机制，更侧重关注稳定的障碍层对上层海洋的反馈效应。通过分析丰富的现场温盐观测、结合卫星遥感资料和高分辨率数值模式输出，揭示混合层/温跃层/障碍层相互影响下的南海上层动力学过程，探讨在南海各关键海区的降雨型、平流型和活跃涡旋中的障碍层变化的维持机制；并进一步基于对南海上层模拟较好的ROMS 海洋模式，通过设置去除或保留障碍层的敏感性试验和动力学诊断，探讨南海上层盐度和障碍层的变化，对南海上层海洋的反馈和区域海气过程的潜在影响。以期为南海海气相互作用研究以及季风气候预报提供更深一步的理论依据。

南海的盐致障碍层由于其独特的海气反馈特征，对上层海洋热力结构和环流有重要影响，可能与南海暖水的形成、南海局地异常增暖等密切相关。本项目在明确南海上层盐度的垂向层结和障碍层分布特征的基础上，研究障碍层对海气过程的多时空尺度的响应机制，更侧重关注稳定的障碍层对上层海洋的反馈效应。.围绕本项目主题<南海盐致障碍层及其对区域海气相互作用的影响>，按照研究计划，通过分析丰富的现场温盐观测、结合卫星遥感资料和高分辨率数值模式输出，揭示混合层/温跃层/障碍层相互影响下的南海上层动力学过程，探讨在南海各关键海区的降雨型、平流型和活跃涡旋中的障碍层变化的维持机制；探讨南海上层盐度和障碍层的变化，对南海上层海洋的反馈和区域海气过程的潜在影响。.本项目的主要结果主要侧重以下4个方面：.（a）数据集的建立：收集现场观测，建立了南海融合观测数据集SCSPOD14和南海潜热通量数据集SCSSLH。提供了南海气候态温盐三维数据以及混合层、温跃层和障碍层数据，以及日/周/月平均的蒸发、潜热和淡水通量数据。.（b）盐度和障碍层的季节和年际变化：从能量学和划分主导机制的角度，详细分析了南海障碍层的统计特征，季节变化，形成和衰减的热动力机制。基于南海北部十年开放航次，研究了南海北部上层层化和障碍层的年际变化情况。结合卫星和SCSPOD14数据集，首次发现2012年这一极端淡化事件并探讨了其引发机制。.（c）盐致障碍层和温度锋对区域海气的影响：探讨了障碍层对混合层温度和上层海洋热含量的增暖效应，南海北部温度锋面对海表风速影响的季节和年际变化；南海西部中尺度涡旋和层结对季节内震荡的影响。.（d）数值模式改善：在数值模式试验期间，针对区域海洋模式POM模式，用交替蛙跳格式替代原蛙跳格式，同时改进了其正斜压时间分裂方法。.通过本项目的实施，所建立的数据集为南海区域海气相互作用提供重要的观测事实，关于障碍层热动力机制和增暖效应的研究可为南海海气相互作用研究以及季风气候预报提供更深一步的理论依据。.