等密度坐标内潮伴随同化模型在参数反演及南海东北部内潮研究中的初步应用

发布时间：2018-05-04 05:17

本文选题：伴随同化 + 内潮　；参考：《中国海洋大学》2014年博士论文

【摘要】：内潮是指具有潮汐频率的一种低频内波,密度层化的海水中表面潮与海底的跃变地形发生相互作用可以生成内潮。内潮在大洋中是普遍存在的,是一种重要的海水运动形式。一方面,内潮在表面潮能量的耗散以及深海混合过程中具有非常重要的作用,进而对深海环流产生重要的影响。另一方面,大振幅的内潮或者由其演变的强孤立内波对石油钻井平台以及海底管道的安全生产与维护非常重要,对经行船舰的安全也构成严重威胁；同时,内潮的生成及传播规律对海洋渔业生产和能源开发等方面也具有重要的研究价值。伴随同化方法是一种有效的四维变分同化技术,它以海洋动力模型作为约束条件,通过同化可观测的时空分布的海洋要素对无法观测到的海洋要素进行反演,实现了数值模型与观测资料的有机结合,提高了数值模拟的精度。本文对伴随同化方法在南海东北部内潮数值模拟中的应用进行了研究。本文首先简要介绍了等密度坐标内潮伴随同化数值模型。该模型在垂向采用等密度坐标,在水平方向采用球坐标,它由正向模型(等密度坐标内潮数值模型)和反向模型(伴随模型)组成,均采用内外模态分离技术。该模型通过将内潮数值模型与观测数据有机结合,来优化模型中的参数,以提高内潮模拟的精度。本文接下来围绕该模型中控制变量的反演问题展开了细致的研究。随后,基于等密度坐标内潮数值模型,探讨该模型模拟内潮的稳定性。最后在优化控制变量的基础上,利用等密度坐标内潮数值模型将伴随同化技术应用到内潮的数值模拟中,初步探讨了海水季节层化因素对南海东北部内潮的影响。本文先将等密度坐标内潮伴随同化模型发展为垂向三层模式,以吕宋海峡为目标海区,探讨了开边界条件的反演问题。随后对空间分布的底摩擦系数的反演问题进行了研究。数值实验研究表明：该伴随同化模型对多种开边界条件和空间分布的底摩擦系数具有较强的反演能力；适当的独立点方案可以进一步提高控制变量的反演精度,以期精确再现全场的内潮结构；代价函数及其关于控制变量的梯度模和同化误差对反演效果具有较强的表征能力,可以综合反映控制变量的反演情况。本文基于等密度坐标内潮数值模型在不同二维高斯地形上,对该模型模拟内潮的稳定性进行了初步探讨,结果表明：低地形下该模型模拟内潮可以达到稳定；虽然高地形下模型的稳定性有待进一步研究,但是利用该模型模拟第100～300个周期的结果可以用来分析内潮。作为该模型初步的实际应用,本文通过同化T/P (TOPEX/Poseidon)高度计资料对南海东北部吕宋海峡附近海域M2内潮的季节变化进行了数值模拟。数值模拟结果表明：通过优化模型中的控制变量,实现了内潮数值模型与观测数据的有机结合；瞬时纬向斜压流在吕宋海峡两个海脊之间较强；吕宋海峡处生成的内潮分别向东、西和西南三个方向传播；在吕宋海峡附近海域,对于第二层纬向斜压流的振幅,夏季的振幅大于冬季的振幅。
[Abstract]:Internal tide is a low frequency internal wave with tidal frequency. The intertidal interaction between the surface tide in the density stratified sea water and the leaping terrain of the seabed can generate internal tide. The internal tide is common in the ocean and is an important form of sea water movement. On the one hand, the internal tide is dissipated in the surface tidal energy and in the deep sea mixing process. On the other hand, large amplitude internal tides or strong isolated internal waves are very important for the safe production and maintenance of oil drilling platforms and submarine pipelines, and a serious threat to the safety of the ship ships; at the same time, the formation and propagation of internal tides are on the ocean. The study of fishery production and energy development also has important research value. The adjoint assimilation method is an effective four dimensional variational assimilation technology. It uses the ocean dynamic model as a constraint condition to invert the unobserved marine elements by assimilating the observable spatiotemporal distribution of ocean elements, and realizes the numerical model and observation. The combination of data improves the accuracy of numerical simulation. In this paper, the application of Adjoint Assimilation Method in numerical simulation of internal tide in the northeast of the South China Sea is studied.
In this paper, the numerical model of tidal concomitant assimilation in equal density coordinates is briefly introduced. The model uses the equal density coordinate in vertical direction and the spherical coordinates in the horizontal direction. It consists of the forward model (the tidal numerical model in the ISO density coordinate) and the reverse model (the adjoint model). The model is used for the internal and external modal separation technology. The model is combined with the observation data to optimize the parameters in the model to improve the accuracy of the internal tide simulation. Next, this paper focuses on the inverse problem of the control variables in the model. Then, based on the tidal numerical model in the ISO density coordinate, the stability of the model is discussed. Finally, the base of the control variable is optimized. On the basis of this, the adjoint assimilation technology is applied to the numerical simulation of internal tide by using the tidal numerical model in ISO density coordinates, and the influence of seasonal stratification factors on the internal tide in the northeast of the South China Sea is preliminarily discussed.
In this paper, the tidal adjoint assimilation model in the ISO density coordinate is first developed into a vertical three layer model, and the inverse problem of the open boundary condition is discussed in the Luzon Strait as the target sea area. Then the inverse problem of the bottom friction coefficient of the spatial distribution is studied. The bottom friction coefficient of the inter distribution has a strong inversion ability, and the appropriate independent point scheme can further improve the inversion accuracy of the control variables, in order to reproduce the internal tide structure of the whole field, and the cost function and the gradient model and the assimilation error of the control variables have strong characterization, which can reflect the control of the inversion. Inversion of variable variables.
In this paper, based on the tidal numerical model of ISO density coordinates in different two-dimensional Gauss terrain, the stability of the model is preliminarily discussed. The results show that the model can be stable under the low terrain. Although the stability of the model in the highland shape needs to be studied further, the model is used to simulate 100th ~ 30. The results of the 0 cycles can be used to analyze the internal tide. As a preliminary practical application of this model, the numerical simulation of the seasonal variations of the internal tide in the waters near the Luzon Strait in the northeast of the South China Sea is simulated by assimilating the T/P (TOPEX/Poseidon) altimeter data. The numerical simulation results show that the control variables in the model have been achieved by optimizing the control variables in the model. The tidal numerical model is combined with the observation data; the instantaneous zonal pressure flow is stronger between the two ridges in the Luzon Strait, and the internal tides in the Luzon Strait spread to three directions in the East, West and southwest respectively. In the waters near the Luzon Strait, the amplitude of the second latitudinal pressure flow is greater than the amplitude in the winter.

【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P731.23

【参考文献】