海洋环流与波动重点实验室知识库

西太平洋具有复杂的三维海洋环流结构。表层流和次表层流的系统是三维结构的重要组成部分，在维持整个大洋质量守恒、热量平衡以及气候预测过程中扮演着不可忽略的角色。以往观测资料有限，热带西太平洋海流研究主要基于水文资料（温盐密），研究其季节到年际变化等，无法知晓西太环流的季节内变化。近几年来，直接测流资料发现季节内变化在热带西太平洋海流变化中占有很大的贡献。研究季节内变化能量来源是来自大气强迫还是来自海洋自身有重要意义。

本文中第一部分工作，针对的科学问题是同纬度的海表面高度季节内变异是否在经向上存在空间和时间周期差异？利用1993–2017年，25年间的海表面高度异常（Sea Level Anomaly，SLA）数据集，首先分析研究了热带西太平洋海表面高度季节内变异（周期：20–120天）的整体分布特征，结果表明空间上季节内信号在20°N附近海域（16°–24°N）最强，且季节内变异存在季节尺度的变化，在6–8月达到一年中的最强，12–2月对应的为一年中的最弱。随后对20°N纬度带海表面高度季节内变异展开分析，结果表明在吕宋海峡东侧海域的季节内信号周期和传播速度均大于吕宋海峡西侧，具体是东侧周期约70天, 传播速度约10.7–12.7 cm/s; 西侧对应的周期为60天, 传播速度6.5–7.8 cm/s。进而分析了在吕宋海峡附近海域和大洋内部的海表面高度季节内变率之间的差异，在大洋内部存在准90 天的周期信号，经计算传播速度约10.3 cm/s。海表面高度季节内变异信号从大洋内部沿纬度平行西传至吕宋海峡东侧海域，在123°E附近传播路径受向北流的黑潮的影响发生改变，由沿纬度平行西传转向向西北方向传播。最后计算了第一斜压Rossby波的波速和理论周期，认为大洋内部的海表面高度的季节内变异的周期和传播速度可以用第一斜压Rossby波的理论周期和波速得到很好的解释。而对吕宋海峡附近海域的海表面高度季节内变率没有很好的解释，猜测吕宋海峡附近海域的海表面高度的季节内变率与局地流场有关。

本文第二部分工作，针对的科学问题是：以往对于北赤道流（North Equatorial Current，NEC）输送多是基于模式数据和历史温盐数据结合地转关系进行估算，对于利用锚系潜标断面观测数据直接计算NEC输送量这一科学问题，前人学者并未有所涉及，进一步对NEC整体输送季节内变异特征研究的工作几乎没有；另外，利用锚系潜标断面观测数据对北赤道潜流（North Equatorial Undercurrent，NEUC）输送的季节内变异的研究工作更是鲜有学者提及。本部分工作基于130°E断面的五套潜标一年的观测数据对NEC和NEUC输送的季节内变异展开，结合RG-Argo和WOA18的两套气候态温盐数据集以及OFES海洋模式数据资料共同分析。首先分析了潜标观测到NEC和NEUC的基本结构，验证了之前学者提出的NEUC具有三支急流的结构，三个核心分别位于8.5°N（〜500 m），12.5°N（〜700 m）和17.5°N（〜900 m），其中中间核心（12.5°N）最强。同时可见随着纬度的增加，三个核心的深度逐渐加深。随后根据潜标观测纬向速度数据估算的NEC的体积输送为52（±14）（1Sv≡10⁶m³s^-1），最大值为83 Sv，方向为向西输送；对应的NEUC的体积输送是18（±13）Sv，最大值为61 Sv，方向为向东输送。对二者做功率谱发现NEC和NEUC的输送具有共同的准40天的季节内变异信号。进而通过EOF分析表明二者的变异性具有相似的垂直空间分布，而且二者输送具有同相位的变异，即当NEC向西的输送减弱时，NEUC向东的输送增强，反之亦然，可以认为是整体断面上存在同向变异。研究中分别使用了两套气候态温盐数据计算纬向地转流，其中依据RG-Argo数据计算的结果与潜标观测结果更加吻合。另外使用QSCAT-OFES模式数据对观测断面进行模拟，纬向速度结构基本上与潜标观测的结果一致，本文使用模式数据计算NEC和NEUC的输送，结果显示二者存在准40天的季节内变异信号。本文也计算了卫星高度计观测的130°E断面，8.5°–17.5°N纬度带之间海表面向西的输送，结果同样具有准40天的季节内变异。最后将两支海流输送的季节内变率和海表面高度的季节变率看作一个整体，通过与大气中季节内振荡的信号MJO进行分析，认为NEC和NEUC输送的准40天变率可能与MJO不同相位之间的转换有关。具体的作用过程在日后的工作中有待进一步研究分析。

Due to the unique geographical location of the western tropical Pacific Ocean, it has a complex three-dimensional ocean currents structure. Surface and subsurface current systems are an important element of the three-dimensional structure, and they play an important role in maintaining the mass conservation, heat balance, and climate prediction of the entire ocean. In the past, observation data was limited, and the study of the western tropical Pacific currents was mainly based on hydrological data (Temperature, salinity, density) to study its seasonal to interannual variability. It is impossible to know the intraseasonal variability of the western Pacific currents. In recent years, direct observation data have found that intraseasonal variability have contributed greatly to variability in the western tropical Pacific currents. Therefore, it is of great significance to study whether the source of energy for intraseasonal variability comes from atmospheric forcing or the ocean's own variability.

The first part of the work in this article is aimed at the scientific question: Is there a spatial and temporal difference in the meridional direction of the intraseasonal variability of sea surface height at the same latitude? Utilized the sea level anomaly (SLA) dataset from 1993 to 2017, the overall distribution characteristics of intraseasonal variability (periods: 20–120 days) in the sea surface height of the tropical western Pacific Ocean were first analyzed. The intraseasonal signal is the strongest in the region around 20°N (16°–24°N), and there is a seasonal scale change in the intraseasonal variability, which reaches the strongest of the year in June–August, and the weakest of the year corresponds to the December–February. The subsequent analysis of the intraseasonal variability in the sea surface height in the 20°N latitude region revealed that the intraseasonal signal period and propagation speed in the east side of the Luzon Strait are greater than those in the west side of the Luzon Strait, specifically about 70 days on the east side, the propagation speed is about 10.7–12.7 cm/s; the corresponding western period is 60 days, and the propagation speed is 6.5–7.8 cm/s. Furthermore, the difference between the intraseasonal variability of the sea surface height near the Luzon Strait and the open ocean is analyzed. There is a quasi-90-day periodic signal in the open ocean, and the calculated propagation speed is about 10.3 cm/s. The intraseasonal signal of sea surface height propagates westward along the latitude from the ocean to the east of the Luzon Strait. The propagation path turns northwestward near the 123°E due to the influence of the Kuroshio. Finally, the wave velocity and theoretical period of the first baroclinic Rossby wave are calculated. It is believed that the intraseasonal variability period and propagation velocity of the sea surface height in the open ocean can be well explained by the theoretical period and wave velocity of the first baroclinic Rossby wave. However, the intraseasonal variability of sea surface height near the Luzon Strait is more related to the role of local background flow field.

The other part of this article is aimed at the scientific question that the North Equatorial Current (NEC) transport was mostly estimated based on model data and hydrological data combines geostrophic equations. For the directly calculating the NEC transport volume using the mooring observation data, previous scholars have not dealt with it, and there is little work to further analyze the intraseasonal variability characteristics of the transport of NEC. In addition, few scholars have mentioned the research work on the intraseasonal variation of the North Equatorial Undercurrent (NEUC) transport using the mooring observation data. This part of the work is based on the one-year observation data from five moorings at the 130°E section to expand the intraseasonal variability transport by NEC and NEUC, and combines the two sets of climatology temperature-salinity data of RG-Argo and WOA18, and OFES model data. Firstly, the mean structures of NEC and NEUC observed by the mooring observation were analyzed, and it was verified that the NEUC proposed by previous scholars has a structure of three jets. The three cores are located at 8.5°N (~500 m), 12.5°N (~ 700m) and 17.5°N (~900 m), with the middle core (12.5°N) being the strongest. It is obvious that as the latitude increases, the depth of the three cores gradually deepens. Subsequently, the volume transport of NEC estimated from the mooring observations was 52 (± 14) Sv (1Sv≡10⁶m³s^-1), with a maximum of 83 Sv, and the direction is westward; the corresponding NEUC volume transport was 18 (± 13) Sv, with a maximum of 61 Sv, and the direction is eastward. The power spectrum analysis shows that the NEC and NEUC transport have a common intraseasonal variability signal of quasi-40-day. Furthermore, EOF analysis shows that the variability of the two has a similar vertical spatial distribution, and the transport of the two has the consistent phase change. That is, when the transport of NEC westward weakens, the transport of the NEUC eastward increases, and vice versa. The variation of th NEC is vertically coherent with NEUC. In the study, two sets of climatology temperature-salinity data were used to calculate the zonal geostrophic flow, and the calculated results based on the RG-Argo data were more consistent with the mooring observation. In addition, QSCAT-OFES model data is used to simulate the observation section. The zonal velocity structure is basically consistent with the results of mooring observations. This paper also calculated the transport of the NEC and NEUC by model data, and the results shown that there is a quasi-40-day intraseasonal variability signal. In this paper, we also calculated the 130°E section observed by the altimeter and transported the sea surface westward between the latitudinal bands of 8.5°–17.5°N. The results also have a quasi-40-day intraseasonal variability signal. Finally, considering the intraseasonal variation of the two currents and the intraseasonal variation of sea surface height as a whole, through composite analysis with the signal of MJO, it is believed that the quasi-40-day variability of NEC and NEUC transport may be related to the conversion between different phases of MJO. The specific process needs further research and analysis in future work.