Turbulence and mixing in a freshwater-influenced tidal bay: Observations and numerical modeling

对垂直剪切应力(雷诺应力)、湍动能剪切生成率与湍动能耗散率以及垂直涡黏性系数等湍流参数的现场观测与数值模拟,是理解强潮海湾中垂直混合过程及其动力与生物地球化学效应的基础.利用坐底AdCP流速观测资料、湍流剖面观测资料以及二阶湍流封闭模型,本文对一典型强潮海湾(厦门湾)中的湍流混合过程进行了观测与数值模拟研究.观测结果表明:在M2分潮占优的厦门湾中,湍动能剪切生成率与湍动能耗散率等湍流参数呈现明显的M4分潮周期,并具有显著的涨-落潮不对称性,涨潮时强,落潮时弱.在涨潮期间,整个水体在垂向上近似混合均匀,湍动能剪切生成率和垂直涡黏性系数的垂向平均值分别达到5x10-6 M2 S-3和2x10-2 M2 S-1;在落潮期间,强湍流则主要局限于厚度为5~8 M的底边界层内,且湍流强度随离底距离的增大而逐渐减小.基于重力位能异常控制方程的分析表明,潮流拉伸是造成湍流强度涨-落潮不对称性的主要原因,潮混合的贡献较小.基于二阶湍流封闭模型的模拟结果与实测结果的对比分析表明,在弱层化强潮海湾中,二阶湍流封闭模型能够较好地模拟湍动能耗散率与垂直涡黏性系等湍流参数的垂向结构与潮内变化;模拟结果与实测值之间的差异主要源于一些理想化的模型假设和数学近似.国家自然科学基金项目(批准号:41006017;41476006); 福建省自然科学基金项目(编号:2015J06010)资

南海北部海域跃层上部的湍流耗散

频发的非线性内波(内孤立波)与内潮活动是南海北部上层海洋动力的重要特征,特别是在南海东北部东沙群岛邻近海域,内孤立波与内潮活动非常活跃,大量的内孤立波与内潮能量在此耗散掉,产生很强的湍流混合.然而,目前国内外对南海北部海域湍流耗散与混合的直接观测研究还非常有限,且主要局限于对吕宋海峡邻

Upper pycnocline turbulence in the northern South China Sea

The first regional mapping of the averaged turbulent kinetic energy dissipation rate aOE (c) E > (p) > in the upper pycnocline of the northern South China Sea is presented and discussed. At phi = 20A degrees N and to the north of this latitude, aOE (c) E > (p) > appears to be more than two times larger than that to the south of 20A degrees N. It is suggested that this asymmetry is associated with the predominant northwestward propagation and dissipation of the internal waves originated in the Luzon Strait area. An approximately linear relationship between aOE (c) E > (p) > and the available potential energy of the waves P (IW), suggests a characteristic time of the P (IW) dissipation of about 6 h.State Key Laboratory of Marine Environmental Science (Xiamen University); National Basic Research Program of China [2009CB421200, 2007CB411803]; National Natural Science Foundation of China [41006017, 41076001]; Fundamental Research Funds for the Central Universities of China [2010121030]; U.S. Office of Naval Research [N00014-05-1-0245

基于SODA资料的南海表层风能输入的空间分布与长期趋势研究

海面风不仅是驱动上层海洋运动的主要动力,其能量也是维持海洋表层流动的主要机械能来源。为了分析南海表层流风能输入的变化,用SODA(Simple Ocean Data Assimilation)(1901—2010)资料估算了风向南海表层流(表层地转流+表层非地转流)的能量输入。结果表明,风向南海表层流、表层地转流和表层非地转流输入的能量总体均呈减少趋势, 110年间分别减小了约56%、65%和49%。导致风能输入减小的最主要因素是风应力的减弱(减小了35%)。由于南海受季风系统的控制,风向表层流及其各成分输入的能量呈现出显著的季节性变化。冬季风能输入最强,高值区位于南海西部及北部区域,呈一个显著的\"回力镖\"状结构。这些结果对深入认识南海环流具有理论意义。国家自然科学基金项目(41676021、41541040、91228202);;近海海洋环境科学国家重点实验室开放课题(MELRS1608)~

Marginal Instability?

Some naturally occurring, continually forced, turbulent, stably stratified, mean shear flows are in a state close to that in which their stability changes, usually from being dynamically unstable to being stable: the time-averaged flows that are observed are in a state of marginal instability. By "marginal instability" the authors mean that a small fractional increase in the gradient Richardson number Ri of the mean flow produced by reducing the velocity and, hence, shear is sufficient to stabilize the flow: the increase makes Ri(min), the minimum Ri in the flow, equal to Ri(c), the critical value of this minimum Richardson number. The value of Ri(c) is determined by solving the Taylor-Goldstein equation using the observed buoyancy frequency and the modified velocity. Stability is quantified in terms of a factor, Phi, such that multiplying the flow speed by (1 + Phi) is just sufficient to stabilize it, or that Ri(c) = Ri(min)/(1 + Phi)(2). The hypothesis that stably stratified boundary layer flows are in a marginal state with Phi < 0 and with |Phi| small compared to unity is examined. Some dense water cascades are marginally unstable with small and negative Phi and with Ri(c) substantially less than 1/4. The mean flow in a mixed layer driven by wind stress on the water surface is, however, found to be relatively unstable, providing a counterexample that refutes the hypothesis. In several naturally occurring flows, the time for exponential growth of disturbances (the inverse of the maximum growth rate) is approximately equal to the average buoyancy period observed in the turbulent region

厦门沿海的砂壳纤毛虫(原生动物,纤毛门,砂壳目)

对厦门沿海6个代表性站位砂壳纤毛虫进行了为期1年的采集,共分离鉴定了27种砂壳纤毛虫,其中拟铃虫属Tintinnopsis 20种,薄铃虫属Leprotintinnus 3种,类铃虫属Codonellopsis 2种,领细壳虫属Stenosemella 1种以及网纹虫属Favella 1种。对该5属27种砂壳纤毛虫进行形态学描述,并提供了显微照片,其中侧胀拟铃虫Tintinnopsis ventricosoides Meunier,1910为中国新记录种。国家自然科学基金(91751207和41306125);;海洋公益性行业科研专项经费(201505003-3);;中海石油有限公司项目(CNOOCKJ125FZDXM00TJ001-2014,CNOOC-KJ125FZDXM00ZJ001-2014)资助~