海洋环流与波动重点实验室知识库

中尺度涡旋在全球海洋中普遍存在，作为海洋中重要的物理过程之一，其统计特征和垂向结构是近年来海内外学者们研究的重点。中尺度涡旋对海洋当中的动力过程、能量物质输运、以及一些生物化学过程都起着十分关键的作用，进而影响着大洋环流以及温度、盐度的水平和垂直分布特征。因此，中尺度涡旋具有非常高的研究和应用价值，它不仅体现在海洋动力学等理论研究中，还体现在国防军事等实际应用中。

基于三个独立的中尺度涡旋数据集，我们提取并统计了1993-2018年全球海洋的中尺度涡旋，详细分析了它们的统计特征，对不同区域的中尺度涡旋基本特征进行了对比；利用四种概率密度函数对涡旋的振幅、半径、旋转速度和罗斯贝数的分布直方图进行拟合，发现对数正态分布能更好的描述涡旋特征的概率分布。在此基础上，以南海北部至吕宋海峡东侧海区为例，结合多年的历史温盐剖面现场观测数据和卫星遥感得到的海面温度（SST）、海面高度（SSH）数据，对三维海洋温盐场进行了扩展，利用观测数据检验了扩展温盐场的可靠性和有效性，并通过三维温度场的结构特征及变化刻画了海面以下的中尺度涡旋特征。

首先，本文给出了全球海洋中尺度涡旋的振幅、半径、旋转速度和罗斯贝数的分布直方图和四个概率密度函数的拟合曲线。对数正态分布的拟合均方根误差最小，是最符合全球海洋中尺度涡旋特征的分布函数，且拟合结果与涡旋数据集的选择无关。之后，通过分析各个大洋中尺度涡旋的特征，我们得到了与全球海洋相似的结果。中尺度涡旋特征的分布均很好地服从于对数正态分布，但不同大洋的拟合均方根误差具有明显的差异。

进一步，本文分析了四个涡旋活跃区域中尺度涡旋的统计特征，不同于大洋区域，这些活跃区域的涡旋特征值明显增大，气旋涡和反气旋涡之间的差异也更加明显。这些结果体现出了显著的区域性特征，其可能与所研究区域的背景流场、层结和斜压不稳定有关，而对数正态分布仍然是拟合活跃区域中涡旋特征分布的最佳函数，且该区域的拟合均方根误差明显降低。说明对数正态分布对不同海区中尺度涡旋特征的拟合均方根误差与涡旋的活跃程度有关，在涡旋更加活跃的区域，拟合均方根误差最小，拟合效果也更好。此外，以STCC区域为例，本文详细分析了中尺度涡旋特征的空间分布、移动特征、季节变化以及年际变化，得到的结果基本与已有的研究成果一致。

为了更好的认识海表面以下的中尺度涡旋特征，我们选取了南海北部至吕宋海峡东侧海区的历史温盐剖面数据，利用回归统计分析的方法，构建了海面温度异常、海面高度异常联合反演温度剖面的经验回归模型，进而采用卫星遥感SST和SSH数据反演得到了该区域时间分辨率为天，空间分辨率为0.25°×0.25°的扩展温度场。此外，利用同样的方法建立由温度反演盐度的经验回归模型，反演得到了该区域的扩展盐度场。

通过与近30年来南海北部至吕宋海峡东侧海区实测数据的对比研究，结果表明反演得到的扩展温度剖面的月平均均方根误差普遍小于1.0°C，其中温跃层附近的误差较大，最大值达到1.55°C ；反演得到的扩展盐度剖面的月平均均方根误差普遍小于0.25 psu，在夏季海面附近较大，达到0.7 psu左右；反演得到的单个观测站点的温盐剖面同样与实际观测结果相近。此外，反演得到的扩展温度场能够清晰地反映出海洋断面温度场的垂直结构和其中的中尺度涡旋特征，并且准确地展示了某一观测区域在吕宋暖涡影响下其三维温度场的结构和变化特征。

Mesoscale eddies are universal in the global ocean. As an important physical process in the ocean, the statistical characteristics and three-dimensional structure of eddies are the focus of domestic and foreign scholars in recent years. Mesoscale eddies play a key role in energy, material transport, and other biochemical processes in ocean dynamics, which further affect the ocean circulation, horizontal and vertical distributions of temperature and salinity. Therefore, the study on mesoscale eddies have a high research and utilization value not only in the theoretical research such as ocean dynamics, but also in the practical applications such as military defense.

Based on three independent mesoscale eddy datasets, we selected eddies in the global ocean from 1993 to 2018, then analysed the statistical characteristics of them and the comparisons with the basic features of mesoscale eddies in different regions. Futhermore, four probability density functions were used to fit the distribution histograms of the eddy’s amplitude, radius, rotation speed and Rossby number. The results showed the lognormal distribution is the best choice to describe the distributions of eddy characteristics. On this basis, taking the northern of the South China Sea as an example, combined with the historical observations data of the temperature and salinity profiles and the sea surface temperature (SST) and sea surface height (SSH) data from satellite remote sensing, the three-dimensional ocean temperature and salinity fields were expanded, their reliability and availability were examined by observed data. Besides, the characteristics of mesoscale eddies below the sea surface were reflected by the structure and variation of the expanded three-dimensional temperature field.

First, the histograms of eddy amplitude, radius, rotation speed and Rossby number in the global ocean with the fitting curves of four probability density functions are given. The results showed that the fitting error of the lognormal distribution is the smallest, which is the best choice to fit eddies in the global ocean and the fitting results is independent of the selection of datasets. Then, through the comparisons of the characteristics of eddies in different seas, we revealed the similar results. Although they were all well followed by the lognormal distribution, there were obvious differences in the fitting errors of different seas.

Mesoscale eddies in eddy-active regions were further analysed. Unlike the large basins, the values ​​of the studied eddy characteristic were significantly increased in these regions, and the difference between cyclonic and anticyclonic eddies were more obvious. These results reflect the significant regional characteristics, which may be related to the local background flow fields, stratification, and baroclinic instability. However, the lognormal distribution is still the best function for fitting the histograms of eddy characteristics in the eddy-active region, and the fitting errors in these region were significantly reduced. The results showed that in different sea regions, the fitting errors of the lognormal distribution on the characteristic of mesoscale eddies are related to the activities of eddy. Where eddies are more active, the fitting errors are smaller and the fitting effects are better. Futhermore, the spatial distribution, propagation characteristics, seasonal and interannual changes of eddies in the STCC region were analysed and the results are consistent with the previous studies.

In order to better understand the characteristics of mesoscale eddy inside the ocean, we selected the historical observations of the temperature and salinity profiles from the northern of the South China Sea to the east of the Luzon Strait. Then an empirical regression model was constructed by the method of regression statistical analysis, which is used to expand the three-dimensional temperature field in this region with a time resolution of day and a spatial resolution of 0.25°×0.25° by the SST and SSH data from satellite remote sensing. Furthermore, the same method was used to establish an empirical regression model to expand the three-dimensional salinity field by temperature field in there.

Comparing with the observed data for past 30 years from the northern of the South China Sea to the east of the Luzon Strait, the results showed that the monthly errors of the expanded temperature profiles are generally less than 1.0°C, which are slightly larger near the thermocline and the maximum is 1.55°C. The monthly errors of the expanded salinity profiles is generally less than 0.25 psu and reach about 0.7 psu near the sea surface in summer. The expanded temperature and salinity profiles at single stations were also similar to the actual observed results. Furthermore, the expanded temperature and salinity field clearly described the temperature vertical structure of a cross section, and accurately simulated the structure and variation of the three-dimensional temperature profile in an observed region under the influence of the Luzon Warm Eddy.