基于1993-2014年高度计数据的西北太平洋中尺度涡识别和特征分析

本文利用22年的AVISO卫星高度计融合数据,基于WA涡旋自动识别方法对西北太平洋的中尺度涡进行了识别追踪,并统计分析了研究区域中尺度涡的空间分布特征、运动属性以及季节和年际变化。研究结果表明:22年间共追踪到生命周期超过30 d的气旋涡3 841个,反气旋涡2 836个,气旋涡数量多于反气旋涡。涡旋大部分向西移动,西向传播的涡旋分布在整个研究区域,而东向传播的涡旋则集中在黑潮及其延伸区。涡旋主要存在15°~30°N的纬度带间;分别而言,气旋涡主要分布在研究区域的北部和南部,而反气旋涡主要分布在副热带逆流区。30°~35°N之间的黑潮延伸区具有明显更高的涡动能和涡振幅,与同纬度区域相比这里的涡旋半径也较高。在季节和年际变化上,春季出现的中尺度涡最多,夏季最少;对涡旋的月生成数目与ENSO指数MEI比较发现,西北太平洋涡旋活动变化并不直接与ENSO现象相关。     

黑潮延伸体区域50-100公里涡旋分布特征

本文使用基于热成风速度的涡旋识别拓展方法,通过海表面温度数据对黑潮延伸体区域50-100公里涡旋进行研究,发现50-100公里涡旋主要分布在黑潮延伸体流轴两侧,气旋涡和反气旋涡的寿命、半径分布具有一致性。气旋涡多出现在35°N以北,反气旋涡在35°N以南比较集中,与尺度较小的中尺度涡旋分布特征较为相似。冬夏两季涡旋地理分布存在一定差异,主要与不同季节该区域海表温度梯度及风应力旋度的变化有关。35°N以南50-100公里涡旋数量的季节性变化与风速大小的季节性变化存在明显的正相关性。35°N以南50-100公里涡旋三倍半径内风速异常和风应力旋度归一化表明,气旋涡对应风速负异常而反气旋涡对应风速正异常,反气旋涡的产生依赖于风应力负旋度,气旋涡的生成与风应力正旋度有关。     

黑潮延伸体区域50~100 km涡旋分布特征

本文使用基于热成风速度的涡旋识别拓展方法,通过海表面温度数据对黑潮延伸体区域50~100 km涡旋进行研究,发现50~100 km涡旋主要分布在黑潮延伸体流轴两侧,气旋涡和反气旋涡的寿命、半径分布具有一致性。气旋涡多出现在35°N以北,反气旋涡在35°N以南比较集中,与尺度较小的中尺度涡旋分布特征较为相似。冬夏两季涡旋地理分布存在一定差异,主要与不同季节该区域海表温度梯度及风应力旋度的变化有关。35°N以南50~100 km涡旋数量的季节性变化与风速大小的季节性变化存在明显的正相关性。35°N以南50~100 km涡旋三倍半径内风速异常和风应力旋度归一化表明,气旋涡对应风速负异常而反气旋涡对应风速正异常,反气旋涡的产生依赖于风应力负旋度,气旋涡的生成与风应力正旋度有关。     

两个西边界流延伸体区域中尺度涡统计特征分析

黑潮和湾流是世界大洋中最典型的两支西边界流，黑潮延伸体（Kuroshio Extention，KE）和湾流延伸体（Gulf Stream Extention，GSE）区域中尺度涡活动十分活跃。本文综合利用卫星高度计资料和Argo浮标资料，对KE和GSE区域中尺度涡的表层特征及其对温盐影响进行了统计研究和对比分析。结果表明:黑潮和湾流主轴附近为涡旋频率的高值区，主轴南北两侧分别以气旋涡和反气旋涡数量占多，主轴附近的涡旋强度明显大于其他区域；两个区域的涡旋以西向移动为主，气旋涡和反气旋涡都具有向南（赤道）偏离的趋势；两个区域的涡旋数量都以夏、秋季较多，涡旋强度都在春、夏季较大，且GSE区域涡旋强度明显大于KE区域；气旋涡（反气旋涡）引起内部明显的温度负（正）异常，KE区域气旋涡（反气旋涡）内部呈"负-正"（"正-负"）上下层相反的盐度异常分布，GSE区域气旋涡（反气旋涡）在各层呈现较为一致的盐度负（正）异常；两个区域中尺度涡对温盐场的平均影响深度可达1 000×104 Pa以上。     

黑潮延伸体海域海平面年际变化及其与海流的关系

利用黑潮延伸体海域海平面异常(SLA)数据和SODA海流资料,分析海平面和海流的年际变化特征,以及两者之间的关系。分析发现黑潮延伸体SLA的第二模态是黑潮大弯曲模态,存在29个月的准两年显著振荡。该海域海平面具有显著的年际变化,且与ENSO和PDO密切相关,2002-2004年的黑潮大弯曲期间,海平面与Nino3指数的相关系数为0.74。海平面年际变化和海流关系密切,黑潮延伸体主轴两侧海平面具有显著的季节和年际变化,急流呈大弯曲路径(1993-1996、2002-2004)时,流轴稳定流速大,流轴影响深,急流主轴南侧海平面较高,达到年际变化的最大值,主轴两侧海面高度梯度大。非弯曲期间,急流主轴南压,海流强度减弱,此期间海平面低,主轴两侧海面高度梯度较小。黑潮延伸体上游区海平面变化受黑潮大弯曲影响更为显著。上下游区的海平面和比容海平面的年际变化较为相似,黑潮延伸体海域海流和比容效应共同调控该区域海平面变化。     

黑潮流轴在吕宋海峡的变化分析

黑潮在流经吕宋海峡时呈现各种时间尺度的流态变化。本文基于高分辨率的区域海洋环流模式(ROMS)输出数据,分析了黑潮主流轴在吕宋海峡附近的变化特征和可能原因。研究结果表明,黑潮流轴在该区域具有明显的年际、季节和季节内变化,其中季节内变化最为强烈;在年际和季节时间尺度上,黑潮流轴在表层主要受局地风驱动的艾克曼漂流的影响,而在次表层则主要由黑潮本身的惯性决定;在季节内时间尺度上,黑潮流轴的变化主要受制于涡旋与黑潮的相互作用。     

黑潮延伸体上游中尺度涡场的年代际振荡及其相关机制

黑潮延伸体上游区域的中尺度涡场的涡动能和涡特征尺度存在显著地年代际振荡,和黑潮延伸体路径的年代际变化有很好的相关性。当黑潮延伸体路径比较稳定时,其上游区域涡动能比较高,涡特征尺度比较大,反之相反。通过对黑潮延伸体上游区域的中尺度涡场进行集合分析发现:当黑潮延伸体处于稳定状态时,上游涡场几乎是各向均匀地,有轻微的径向伸长;而当黑潮延伸体处于不稳定状态时,上游的中尺度涡场有显著地纬向伸长。对与中尺度涡场的产生相关的线性斜压不稳定和正压不稳定进行了计算分析,结果显示,线性斜压不稳定不是控制中尺度涡场年代际变化的机制,而正压不稳定对中尺度涡场的年代际变化有积极的贡献。不稳定产生的中尺度涡之间存在非线性涡-涡相互作用。     

太平洋海气界面净热通量的季节、年际和年代际变化

根据 COADS资料 ,使用经验正交分解 (EOF)等分析方法 ,研究了北太平洋海气热通量的季节、年际和年代际变化特征。分析结果表明 :北太平洋海洋夏季净得热 ,冬季净失热 ,且黑潮及其延伸体区失热最大。净热通量年际变化较明显 ,北太平洋西部模态水形成区冬季净热通量和副热带失热区春季净热通量的年际变化都主要依赖于潜热和感热通量的年际变化。夏季净热通量的低频变化中心在热带 ,冬季低频变化中心在黑潮及其延伸体区。冬季赤道东、西太平洋净热通量异常的年际变化相反 ;在热带北太平洋中部年际变化达到最大。夏季热带太平洋是净热通量异常的年际变化最大的海域 ,沿赤道两侧在 16 5°E处呈偶极子型分布。     

基于拉格朗日拟序结构的吕宋海峡表层水交换研究

黑潮通过吕宋海峡入侵南海呈现明显的瞬态特征。以往的研究通常将黑潮在吕宋海峡附近的流态分为几种不同类型。本文基于表层地转流计算得到的有限时间李雅普诺夫指数场（FTLE），展示了拉格朗日视角下的吕宋海峡上层水交换特征。从FTLE场提取的拉格朗日拟序结构（LCSs）很好地识别了吕宋海峡附近的典型流态和旋涡活动。此外，这些LCSs还揭示了吕宋海峡周围复杂的输运路径和流体域，这些特征得到了卫星跟踪浮标轨迹的验证，且从流速场中是无法直接识别的。FTLE场显示，吕宋海峡附近表层水体的输运形态主要可分为四类。其中，黑潮直接向北流动的“跨越”形态和顺时针旋转的“流套”形态的发生频次明显高于直接进入南海的黑潮分支“渗入”形态和南海水流出至太平洋的“外流”形态。本文还进一步分析了黑潮在吕宋海峡处的涡旋脱落事件，突出强调了LCSs在评估涡旋输运方面的重要性。反气旋涡旋的脱落个例表明，这些涡旋主要源自黑潮“流套”，涡旋脱落之前可有效地俘获黑潮水。LCS所指示的输运通道信息有助于预测最终被反气旋涡所挟卷水体在上游的位置。而在气旋涡的形成过程中，LCS的分布特征表明，大部分气旋涡并未与黑潮水的输运路径相连通。因此，气旋涡对从太平洋到南海的上层水交换的贡献较小。     

A statistical analysis of mesoscale eddies in the Bay of Bengal from 22–year altimetry data

本文使用一种基于SLA数据的涡旋识别方法,通过22年的AVISO高度计测高数据对孟加拉湾的中尺度涡特征进行了研究。本文主要分析了孟加拉湾涡旋的地理分布、涡旋极性、涡旋生命周期和传播距离、涡旋产生和消失位置、涡旋传播方向和移动轨迹、涡旋运动特征、涡旋属性的演化以及涡旋活动的季节和年际变化等特性。涡旋主要分布在孟加拉湾西部海域,并且大部分涡旋向西移动。涡旋极性分布显示气旋涡更经常出现在湾的西北部和南部,而反气旋涡主要出现在湾的东部。在22年间,共追踪探测到生命周期超过30天的气旋涡565个、反气旋涡389个;对所有生命周期和传播距离而言都是气旋涡数量居多。所有观测到的涡旋的运动属性分析显示气旋涡的涡旋平均振幅大于反气旋涡;对平均半径和平均移动速度而言,气旋涡和反气旋涡相差不大。而且,涡旋属性演化显示生命周期超过90天的涡旋具有明显的双阶段演化特征,包括一个前50天的涡旋成长阶段和一个50天之后的涡旋消亡阶段。针对涡旋活动的季节变化,气旋涡在春季居多而反气旋涡在夏季较多;长生命周期的涡旋季节分布显示在孟加拉湾涡旋活动具有明显的季节分布特征。涡旋数量的年际变化与EKE变化有一个明显的负相关。     

The Kuroshio Extension Front from satellite sea surface temperature measurements

The position and strength of the surface Kuroshio Extension Front (KEF), defined as the sea surface temperature (SST) gradient maximum adjacent to the Kuroshio Extension (KE) axis (approximated by a specific SSH contour consistently located at, or near, the maximum of the SSH gradient magnitude), have been studied using weekly, microwave SST measurements from the later 1997 to early 2008. The mean KEF meanders twice around ∼36°N between the east coast of Japan and 153°E. It then migrates southeast to ∼34°N, just before reaching the Shatsky Rise (∼158°E), then progresses mostly eastward. Spatially, the KEF is strongest near the Japan coast, while it is seasonally strongest in winter and weakest in summer. Low-frequency variations of its strength, most notably in its upstream region, can be related to the known bimodal states of the KE. During 2003–2005, when the KE was in its stable state, the winter KEF SST gradient exceeded 10°C/100 km.     

黑潮延伸体区域脱落涡旋的三维合成结构研究

Using AVISO satellite altimeter observations during 1993–2015 and a manual eddy detection method, a total of 276 anticyclonic rings and 242 cyclonic rings shed from the Kuroshio Extension(KE) were identified, and their three-dimensional(3D) anomaly structures were further reconstructd based on the Argo float data and the Japan Agency for Marine-Earth Science and Technology(JAMSTEC) cruise and buoy data through an interpolation method. It is found that the cyclonic(anticyclonic) rings presented consistent negative(positive) anomalies of potential temperature;meanwhile the relevant maximum anomaly center became increasingly shallow for the cyclonic rings whereas it went deeper for the anticyclonic rings as the potential temperature anomaly decreased from the west to the east. The above deepening or shoaling trend is associated with the zonal change of the depth of the main thermocline. Moreover, the composite cold ring between 140° and 150°E was found to exhibit a double-core vertical structure due to the existence of mode water with low potential vorticity. Specifically, a relatively large negative(positive) salinity anomaly and a small positive(negative) one appeared for the composite cyclonic(anticyclonic) ring at the depth above and below 600 m, respectively. The underlying driving force for the temperature and salinity anomaly of the composite rings was also attempted, which varies depending on the intensity of the background current and the temperature and salinity fields in different areas of the KE region, and the rings’ influences on the temperature and salinity could reach deeper than 1 000 m on average.     

Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability

Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.     

Seasonal and interannual variation of North Pacific Subtropical Mode Water in 2003–2006

Temperature and salinity data from 2003 through 2006 from Argo profiling floats have been analyzed to examine the formation and circulation of the North Pacific Subtropical Mode Water (STMW) and the interannual variation of its properties over the entire distribution region. STMW is formed in late winter in the zonally-elongated recirculation gyre south of the Kuroshio and its extension, which extends north of ∼28°N, from 135°E to near the date line. The recirculation gyre consists of several anticyclonic circulations, in each of which thick STMW with a characteristic temperature is formed. After spring, the thick STMW tends to be continually trapped in the respective circulations, remaining in the formation region. From this stagnant pool of thick STMW, some portion seeps little by little into the southern region, where southwestward subsurface currents advect relatively thin STMW as far as 20°N to the south and just east of Taiwan to the west. The STMW formed in the recirculation gyre becomes colder, less saline, and denser to the east, with an abrupt change of properties across 140°E and a gradual change east of 140°E. The STMW formed east of 140°E exhibits coherent interannual variations, increasing its temperature by ∼1°C from 2003 through 2006 and also increasing its salinity by ∼0.05 from 2003 through 2005. These property changes are clearly detected in the southern region as far downstream as just east of Taiwan, with reasonable time lags.     

基于自组织映射的日本南部黑潮与黑潮延伸体的典型时空模态及其因果关系研究

过去的研究认为,黑潮延伸体的年代际振荡受来自其下游的太平洋年代际振荡（PDO）相关联的信号主导,但最近的观测表明这种调控机制在2017年9月之后不再成立。与此同时,黑潮延伸体的上游即日本南部黑潮正在发生一次大弯曲事件。利用26年（1993–2018年）的卫星高度计提供的海表高度距平数据和自组织映射（SOM）方法,本文研究了日本南部黑潮与黑潮延伸体的时空模态及其因果关系。结果表明,SOM能有效地提取两个海区的典型空间模态,且它们的演变轨迹表明当日本南部黑潮处于大弯曲（离岸型非大弯曲）路径时,黑潮延伸体趋于稳定（不稳定）态。基于SOM识别得到的海表面高度距平（SLA）特征区及特征时间模态,我们进一步利用一种最近发展的定量因果分析方法研究了两个流系之间的因果关系。研究发现,当黑潮大弯曲发生时,日本南部黑潮和黑潮延伸体之间存在双向因果,但因果关键区不同。前者对后者的影响集中在纪伊半岛东南侧及黑潮延伸体“两脊一槽”区域,而后者对前者的影响则集中在黑潮延伸体“两脊一槽”区域及黑潮再循环流区域。这说明黑潮大弯曲的发展对黑潮延伸体的稳定性有重要作用,同时黑潮延伸体通过调制南部再循环流影响日本南部黑潮的路径。不同的是,当离岸型非大弯曲路径发生时,只有从日本南部黑潮向黑潮延伸体的单向因果关系,且因果性主要集中在伊豆海脊及再循环流区域。这与该时期海表高度负异常沿日本南岸不断向位于下游的黑潮延伸体再循环流的传播有关,它使得黑潮延伸体变得不稳定。     

1998年冬季南海上层环流诊断计算

基于1998年11月28日至12月27日的调查航次的CTD资料,采用P矢量方法对调查期间南海环流进行了诊断计算,也对比了在此期间TOPEX/ERS卫星高度计SSH的资料,得到了1998年冬季南海上层环流的以下一些重要特征.(1)南海中部环流系统主要特征:在冬季越南近岸出现西边界南向射流.这支沿岸南向射流以东、114°E以西存在一个尺度大的、显著气旋式环流,它位于南自10°N左右北至16°N附近区域.在区域东中部存在一个尺度不大的、较弱的反气旋暖涡.该反气旋涡中心约位于14°N附近.在上述强的气旋式环流涡与较弱的反气旋式环流涡之间,存在一支强的、逆风方向的,即偏东北方向的海流.上述是冬季南海中部基本流态,并与200m处水平温度分布与密度分布有很好的对应.产生上述基本流态的动力原因有两个:1)在偏东北季风作用下,与地形变化相互作用,是本文首次提出的,并指出,其动力原因与冬季黄海暖流形成机制有相似之处;2)由于斜压场与地形的联合效应(JEBAT).(2)在海区南部存在一个反气旋式环流,在加里曼丹岛西北还有一个尺度不大、冷的气旋式涡.(3)南海北部环流系统:1)在吕宋岛西北明显地存在一个气旋环流系统,并有3个冷水中心;2)在此气旋式环流系统的一个冷水中心(约19°30'N,119°30'E)以西,存在一个反气旋式涡;3)在海南岛以南出现一个暖的、反气旋式环流;4)在南海北部,114°E以东、广东沿岸外侧存在一支东北向流.这是管秉贤首次指出的,冬季时出现南海暖流.(4)上述1998年冬季南海上层环流的一些重要特征都与此期间TOPEX/ERS-2卫星高度计SSH分布有较好的相对应.     

赤道东印度洋和孟加拉湾障碍层厚度的年际变化及其影响机制

Interannual variability(IAV) in the barrier layer thickness(BLT) and forcing mechanisms in the eastern equatorial Indian Ocean(EEIO) and Bay of Bengal(BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January(NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode(IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth(ILD). Moreover, the variability in the mixed layer depth(MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December–February(DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Ni?o-Southern Oscillation(ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations.     

黑潮延伸体海洋锋强度和位置变率的对比研究

This study compares the seasonal and interannual-to-decadal variability in the strength and position of the Kuroshio Extension front(KEF) using high-resolution satellite-derived sea surface temperature(SST) and sea surface height(SSH) data. Results show that the KEF strength has an obvious seasonal variation that is similar at different longitudes, with a stronger(weaker) KEF during the cold(warm) season. However, the seasonal variation in the KEF position is relatively weak and varies with longitude. In contrast, the low-frequency variation of the KEF position is more distinct than that of the KEF strength even though they are well correlated. On both seasonal and interannual-to-decadal time scales, the western part of the KEF(142°–144°E) has the greatest variability in strength, while the eastern part of the KEF(149°–155°E) has the greatest variability in position. In addition, the relationships between wind-forced Rossby waves and the low-frequency variability in the KEF strength and position are also discussed by using the statistical analysis methods and a wind-driven hindcast model. A positive(negative) North Pacific Oscillation(NPO)-like atmospheric forcing generates positive(negative) SSH anomalies over the central North Pacific. These oceanic signals then propagate westward as Rossby waves, reaching the KE region about three years later, favoring a strengthened(weakened) and northward(southward)-moving KEF.     

南大洋混合层的时空变化特征

过去对南大洋的研究受限于长期观测的缺乏,而现在地转海洋学实时观测阵(Arrayfor Real-timeGeostrophicOceanography,Argo)项目自开始以来持续提供了高质量的温度盐度观测,使系统地研究南大洋海洋上层结构成为可能。本研究使用2000—2018年的Argo浮标观测数据,分析了南大洋混合层深度(Mixed Layer Depth, MLD)的时空分布特征。结果表明:南大洋混合层存在明显的季节变化,冬春两季MLD在副南极锋面北侧达到最高值并呈带状分布,夏秋两季由于海表加热导致混合层变浅,季节变化幅度达到400m以上;在年际尺度上,MLD受南半球环状模(Southern HemisphereAnnularMode,SAM)调制,呈现纬向不对称空间分布特征,这与前人结果一致;本文指出在所研究时段,南大洋混合层在90°E以东,180°以西有加深趋势,而在60°W以西,180°以东有变浅趋势,显示出偶极子分布特征,并且这种趋势特征主要是风场的作用。     

Spreading of Antarctic Bottom Water and its effects on the floor of the Indian Ocean inferred from bottom-water potential temperature,turbidity, and sea-floor photography

Data on bottom-water potential temperature, turbidity and current indications show that in the Southern Ocean west of the Kerguelen Plateau, Antarctic Bottom Water (AABW) of Weddell Sea origin spreads northwards from the Atlantic—Indian Basin in two directions: (1) AABW enters the Agulhas Basin through relatively deep areas in the Mid-Indian Ridge at 20–25°E and possibly at 35°E, and flows northwards into the Mozambique Basin as far as its northern limits; (2) a more easterly spreading path extends from the Atlantic—Indian Basin through the Crozet into the Madagascar, Mascarene, Somali and Arabian Basins. The passage in the western branch of the Indian Ridge for the AABW spreading from the Crozet into the Madagascar Basin appears to be at 29-26°S and 60–64°E.East of the Kerguelen Plateau in the South Indian Basin, the bottom water formed mainly along the Adélie Coast and Ross Sea travels west towards the Kerguelen Plateau and then parallel to it. This water finally flows eastwards hugging the Southeast Indian Ridge. Significant deviations from this general circulation pattern occur due to local topographic effects. Some AABW in the South Indian Basin exits through a passage at 120–125°E in the region of the Australian—Antarctic discordance in the Southeast Indian Ridge and enters the South Australian Basin and subsequently the Wharton Basin. This passage is clearly indicated by the northward extension of a cold, bottom-water tongue as shown by the temperature distribution in the region; the bottom-water effects in the passage are reflected in the high turbidity and current lineations on the sea floor.In the Southern Ocean basins, bottom-water turbidity is generally high, reflecting in part the strong bottom-water activity. The effects of AABW circulation on the sea floor—in the form of well-developed small- or large-scale current ripples and erosional/depositional features, manganese-nodule formations, and unconformities and reworking of sediments observed in cores — are also marked in these basins. Even though the AABW in the Wharton Basin is cold, its spreading effects on the sea floor are minimal in this basin in contrast to the basins west of the Mid-Indian Ridge at comparable latitudes.