【作者】 李爽；

【导师】 宋金宝；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 物理海洋， 2010， 博士

【摘要】 表面波主要通过两种方式影响上海洋混合层(OML)：(1)波浪破碎(WB),WB导致的波浪能量通量可以在海表提供额外湍动能源,同时增强近表层能量耗散；(2) Langmuir环流(LC),风生Stokes漂流与平均流共同作用导致的LC对OML内湍流生成和垂向混合的影响至关重要。尽管它们产生的湍流能量通量仅限于海表几米之内,但是它们却可以影响整个OML内的湍流混合过程。混合层数值模拟,如,湍封闭模型已经被用于模拟OML (Kantha and Clayson,2004; Sun et al.2005),这些模型对于LC和其它混合过程的模拟研究尚不完整。本文利用MY2.5阶湍封闭模式,参照Craig和Banner (1994),通过修改边界条件及模式控制方程中的源函数项等,研究LC与其它动力和热力过程(WB、海表热通量)的相互作用机制,特别是WB和LC共同作用所引起的强混合问题。其中包括研究不同海况下(不同风速、不同破碎强度和不同海表热通量)LC对海洋上层混合(如：混合深度、强度、混合率等)的影响。通过逐一或联合考虑不同风速下、有无WB、不同海表热通量大小时,LC对海洋上层混合的影响。为了更加细致地描述LC和WB对OML内湍流生成机制的相对作用,本文对介于直接数值模拟(DNS)和参数化湍封闭模式之间的三维湍流模拟工具—大涡模拟(LES)进行了改进,使之包含了OML中小尺度动力过程,并针对LC和WB对OML的影响进行数值模拟。通过分析湍动能收支,讨论了标准边界层(剪切和浮力)和考虑波浪影响下的湍流边界层(WB和LC)湍动能收支各项的相对重要性。另外,通过不同风速和不同波浪条件下的理想数值实验,考察了不同海况下LC和WB对混合机制的影响。最后,利用LES方法模拟了伍兹霍尔实验室海气相互作用边界层耦合低风速观测实验(CBLAST-Low),并对湍流Langmuir数Lat大于2(剪切)、Lat,小于1(LC)、风速逐渐增强,风速逐渐减弱以及风速迅速减小五种情况下,比较分析了观测与LES数值实验结果间的异同,研究了LC和WB对湍流生成和混合机制的影响。更多还原

【Abstract】 Surface waves affect the ocean surface mixed layer in two ways:(1) breaking waves inject turbulent kinetic energy at the ocean surface and create a near-surface layer of high energy dissipation; (2) the interaction of wave-induced Stokes drift current and mean wind-driven current generates counter-rotating vortices known as Langmuir circulations. Although both the turbulence energy flux due to breaking waves and the Stokes turbulence production are confined to the ocean surface within the top few meters, they can affect turbulent mixing processes throughout most of the ocean mixed layer.Although mixed layer models such as turbulence closure model have been used to simulate OML (Kantha and Clayson,2004; Sun et al.2005), these models have not adequately quantified LC and other mixing processes. Like Craig and Banner (1994), a modified Mellor-Yamada 2.5 level turbulence closure model is used to parameterize LC and other mixing processes’effects on upper ocean mixing through changing boundary conditions and original equations. Numerical modeling study including how LC affects OML under different sea state (different wind speed, strength of WB and heat flux). Strong mixing processes by interaction between LC and WB are discussed particularly.In order to describe the relative contributions of LC and WB to turbulence generation in OML, a three dimensional Large Eddy Simulation model (LES) is improved by including the small scale processes and used to investigate the effects of LC and WB on OML. By analyzing the turbulent kinetic energy (TKE) budget, the author examines the relative importance of standard boundary layer sources of TKE (shear and buoyancy production) to wave sources of TKE (LC and WB). This includes examination of the depths wave processes can influence. Furthermore, a number of cases under different wind and wave conditions have been conducted and the author assesses the relative importance of WB and LC in the mixed-layer dynamics as a function of sea state.Finally, the author compares the LES model results with the turbulence measurements collected during the CBLAST-Low (Coupled Boundary layers and Air-sea Interaction-Low Winds) experiments by Woods Hole Oceanography Institute in five numerical experiments: turbulent Langmuir number Lat>2 (shear case), Lat<1 (LC case), increasing wind speed, decreasing wind speed and crazy down wind speed cases.更多还原