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西北太平洋中尺度涡旋分类统计与海表温度特征分析
Statistical classification and sea surface temperature characteristics of mesoscale eddies in the Northwestern Pacific
本文基于卫星高度计涡旋数据集，对西北太平洋中尺度涡进行分类统计和特征分析，并通过合成分析法重构各类涡旋对应的海表温度异常（sea surface temperature anomaly， SSTA）和海面高度异常（sea level anomaly， SLA）的空间结构，对海域中尺度涡分布特征展开分析。将研究海域分成北赤道流（North Equatorial Current， NEC）、副热带逆流（Subtropical Countercurrent， STCC）和黑潮延伸体（Kuroshio Extension， KE）三个海域，以11—12月和1—4月为冷季， 5—10月为暖季，按照涡旋极性进行分类、统计和分析。结果显示，研究海域涡旋通常为气旋冷涡与反气旋暖涡，但也存在气旋暖涡和反气旋冷涡两种反常涡旋，反常涡旋的数量占涡旋总数的比例约为22.5%。反常涡旋发生概率为低纬度高于高纬度、暖季高于冷季。常规涡旋的SSTA与其振幅呈正相关，随纬度升高幅值增大，且冷季均值高于暖季；反常涡旋的SSTA整体弱于常规涡旋，且未表现出明显的区域与季节差异。合成分析显示，与常规涡旋相比，反常涡旋形态更偏离圆形，振幅和SSTA变幅较小。
Based on a satellite altimetry-derived eddy dataset， this study conducted a classification-based statistical and characteristic analysis of mesoscale eddies in the Northwestern Pacific. A composite analysis method was further employed to reconstruct the spatial structures of sea surface temperature anomalies （SSTAs） and sea level anomalies （SLAs） associated with different eddy categories and to investigate the distribution characteristics of mesoscale eddies in the study area. The study region was divided into three subregions： the North Equatorial Current （NEC）， the Subtropical Countercurrent （STCC）， and the Kuroshio Extension （KE）. November to December and January to April were defined as the cold season， while May to October were defined as the warm season. Eddies were classified， counted， and analyzed according to their polarity. The results show that mesoscale eddies in the study region are generally characterized by cold-core cyclonic eddies and warm-core anticyclonic eddies. However， two types of abnormal eddies， namely warm-core cyclonic eddies and cold-core anticyclonic eddies， are also identified， accounting for approximately 22.5%of the total eddy population. The occurrence probability of abnormal eddies is higher at low latitudes than at high latitudes， and higher in the warm season than in the cold season. For normal eddies， SSTA is positively correlated with eddy amplitude， increases with latitude， and is generally stronger in the cold season than in the warm season. In contrast， abnormal eddies exhibit overall weaker SSTAs than normal eddies and show no obvious regional or seasonal differences. Composite analysis further reveals that compared with normal eddies， abnormal eddies are less circular in shape and have smaller amplitudes and weaker SSTA variations.
西北太平洋 / 中尺度涡旋 / 海表温度异常 / 空间结构 / 反常涡旋 / 季节变化 / 副热带逆流区 / 黑潮延伸体
Northwestern Pacific / mesoscale eddy / sea surface temperature anomaly / spatial structure / abnormal eddies / seasonal variability / Subtropical Countercurrent region / Kuroshio Extension
| [1] |
杨光. 西北太平洋中尺度涡旋研究[D]. 青岛: 中国科学院研究生院(中国科学院海洋研究所), 2013.
|
| [2] |
|
| [3] |
|
| [4] |
胡冬, 陈希, 毛科峰, 等. 黑潮延伸体邻近区域中尺度涡特征统计分析[J]. 海洋与湖沼, 2018, 49(3):497-511.
|
| [5] |
|
| [6] |
|
| [7] |
刘颖洁, 田丰林, 陈戈. 南海中尺度涡旋海表温度特征统计研究[J]. 中国海洋大学学报:自然科学版, 2020, 50(5):146-156.
|
| [8] |
张铷火, 陈旭, 宁珏, 等. 太平洋中纬度不同区域气旋式暖涡和反气旋式冷涡的结构研究[J]. 海洋与湖沼, 2024, 55(3):599-612.
|
| [9] |
|
| [10] |
|
| [11] |
|
| [12] |
By analyzing 22 years (1993–2015) of daily eddy data, statistics of surface eddy properties were refreshed in the South China Sea. More than 7,000 of historical Argo profiles were collocated into eddy‐centered coordinates to reveal the composite mean three‐dimensional structure of eddies. The results indicate that eddies of both polarities have long conical shape, with a maximum (minimum) density anomaly of 0.55 kg/m3 (−0.51 kg/m3) at 60 m (90 m) in the composite cyclonic (anticyclonic) eddy. Temperature and salinity anomalies also peak at eddy cores, with values of −1.5 °C and 0.15 psu in the cyclonic eddy and 1.4 °C and −0.16 psu in the anticyclonic eddy. The temperature and density anomalies extend vertically to 400–500 m, while the salinity anomalies are apparent only in the upper 150 m. The temperature anomalies contribute about 90% of the density anomalies. Mixed layer depths in cyclonic eddies are on average 15 m shallower than those in anticyclonic eddies. The rotation of the composite cyclonic (anticyclonic) eddy generates meridional heat transport of 1.4 × 1012 W (−3.1 × 1012 W) and salt transport of −4.0 × 104 kg/s (5.6 × 104 kg/s). More than 90% of the heat and salt transports are concentrated in the upper 300 and 100 m, respectively. Compared to the meridional transports, the westward propagation of eddies results in zonal heat and salt transports on the same orders of magnitudes. The westward propagation of eddies also generates a basin‐scale westward water transport of 1.4 Sv, equivalent to about 30% of the annual‐mean Luzon Strait transport.
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| [13] |
汤博, 侯一筠, 殷玉齐, 等. 北太平洋副热带逆流区中尺度涡旋的统计特征及其分布规律[J]. 海洋与湖沼, 2019, 50(5):937-947.
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| [14] |
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| [15] |
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| [16] |
Three mechanisms for self-induced Ekman pumping in the interiors of mesoscale ocean eddies are investigated. The first arises from the surface stress that occurs because of differences between surface wind and ocean velocities, resulting in Ekman upwelling and downwelling in the cores of anticyclones and cyclones, respectively. The second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient, resulting in dipoles of Ekman upwelling and downwelling. The third mechanism arises from eddy-induced spatial variability of sea surface temperature (SST), which generates a curl of the stress and therefore Ekman pumping in regions of crosswind SST gradients. The spatial structures and relative magnitudes of the three contributions to eddy-induced Ekman pumping are investigated by collocating satellite-based measurements of SST, geostrophic velocity, and surface winds to the interiors of eddies identified from their sea surface height signatures. On average, eddy-induced Ekman pumping velocities approach O(10) cm day−1. SST-induced Ekman pumping is usually secondary to the two current-induced mechanisms for Ekman pumping. Notable exceptions are the midlatitude extensions of western boundary currents and the Antarctic Circumpolar Current, where SST gradients are strong and all three mechanisms for eddy-induced Ekman pumping are comparable in magnitude. Because the polarity of current-induced curl of the surface stress opposes that of the eddy, the associated Ekman pumping attenuates the eddies. The decay time scale of this attenuation is proportional to the vertical scale of the eddy and inversely proportional to the wind speed. For typical values of these parameters, the decay time scale is about 1.3 yr.
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| [17] |
Mesoscale eddies are ubiquitous features of the global ocean circulation. Traditionally, anticyclonic eddies are thought to be associated with positive temperature anomalies while cyclonic eddies are associated with negative temperature anomalies. However, our recent study found that about one-fifth of the eddies identified from global satellite observations are cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs). Here we show that in the tropical oceans where the probabilities of CAEs and WCEs are high, there are significantly more CAEs and WCEs in summer than in winter. We conduct a suite of idealized numerical model experiments initialized with composite eddy structures obtained from Argo profiles as well as a heat budget analysis. The results highlight the key role of relative wind-stress-induced Ekman pumping, surface mixed layer depth, and vertical entrainment in the formation and seasonal cycle of these unconventional eddies. The relative wind stress is found to be particularly effective in converting conventional eddies into CAEs or WCEs when the surface mixed layer is shallow. The abundance of CAEs and WCEs in the global ocean calls for further research on this topic.
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| [18] |
A (an) cyclonic (anticyclonic) eddy is usually associated with a cold (warm) core caused by the eddy-induced divergence (convergence) motion. However, there are also some cyclonic (anticyclonic) eddies with warm (cold) cores in the North Pacific, named cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) in this study, respectively. Their spatio-temporal characteristics and regional dependence are analyzed using the multi-satellite merged remote sensing datasets. The CWEs are mainly concentrated in the northwestern and southeastern North Pacific. However, besides these two areas, the ACEs are also concentrated in the northeastern Pacific. The annual mean number decreases year by year for both CWEs and ACEs, and the decreasing rate of the CWEs is about two times as large as that of the ACEs. Moreover, the CWEs and ACEs also exhibit a significant seasonal variation, which are intense in summer and weak in winter. Based on the statistics of dynamic characteristics in seven subregions, the Kuroshio Extension region could be considered as the most active area for the CWEs and ACEs. Two possible mechanisms for CW-ACEs generation are discussed by analyzing two cases.
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| [19] |
Five ice-tethered profilers (ITPs), deployed between 2004 and 2006, have provided detailed potential temperature θ and salinity S profiles from 21 anticyclonic eddy encounters in the central Canada Basin of the Arctic Ocean. The 12–35-m-thick eddies have center depths between 42 and 69 m in the Arctic halocline, and are shallower and less dense than the majority of eddies observed previously in the central Canada Basin. They are characterized by anomalously cold θ and low stratification, and have horizontal scales on the order of, or less than, the Rossby radius of deformation (about 10 km). Maximum azimuthal speeds estimated from dynamic heights (assuming cyclogeostrophic balance) are between 9 and 26 cm s−1, an order of magnitude larger than typical ambient flow speeds in the central basin. Eddy θ–S and potential vorticity properties, as well as horizontal and vertical scales, are consistent with their formation by instability of a surface front at about 80°N that appears in historical CTD and expendable CTD (XCTD) measurements. This would suggest eddy lifetimes longer than 6 months. While the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism, it is less likely since deeper eddies that would originate from the deeper-reaching boundary flows are not observed in the survey region.
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| [20] |
Vertical profile data of temperature and salinity from various sources were analyzed together with satellite altimeter data to investigate the water mass characteristics of warm and cold anticyclonic eddies in the western boundary region of the subarctic North Pacific. A dense distribution of anticyclonic eddies with warm and saline core water occurred near the Kuroshio Extension, and the distribution extends northward–northeastward into the western subarctic gyre along the Japan and Kuril–Kamchatka trenches. Eddies with cold and fresh core water are found mainly around the Oyashio southward intrusions and farther north near the Kuril Islands. Based on the heat content anomaly integrated over 50–200 dbar, 85% of the anticyclonic eddies within the study area (35°–50°N, 140°–155°E) have a warm and saline core and 15% have a cold and fresh core. Warm and saline eddies around the Japan and Kuril–Kamchatka trenches have a double-core structure, with a cold and freshwater mass located below the warm core. The northward propagation of these eddies along the trench line results in a large northward heat (salinity) transport in the upper 400 dbar (250 dbar) and a negative salinity transport below 350 dbar. The lower core water is colder and fresher on isopycnal surfaces at around 26.70σθ compared with the climatology. Given that the 26.70σθ isopycnal surface does not outcrop in the open North Pacific, an alignment process is suggested to occur between the warm and saline and the cold and fresh anticyclonic eddies in the upper and intermediate layers, respectively.
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| [21] |
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| [22] |
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