Spreading and salinity change of North Pacific Tropical Water in the Philippine Sea

Newly formed North Pacific Tropical Water (NPTW) is carried to the Philippine Sea (PS) by the North Equatorial Current (NEC) as a subsurface salinity maximum. In this study its spreading and salinity change processes are explored using existing hydrographic data of the World Ocean Database 2009 and Argo floats. Spreading of NPTW is closely associated with the transports of the NEC, Mindanao Current (MC), and Kuroshio. Estimated for subsurface water with salinity S greater than 34.8?psu, the southward (northward) geostrophic transport of NPTW by the MC (Kuroshio) at 8°N (18°N) is about 4.4 (5.7)?Sv (1?Sv?=?10⁶?m³?s^?1), which is not sensitive to reference level choice. Fields of salinity maximum, geostrophic current, sea level variation, and potential vorticity suggest that the equatorward spreading of NPTW to the tropics is primarily afforded by the MC, whereas its poleward spreading is achieved by both the Kuroshio transport along the coast and open-ocean mesoscale eddy fluxes in the northern PS. The NPTW also undergoes a prominent freshening in the PS. Lying beneath fresh surface water, salinity decreases quicker in the upper part of the NPTW, which gradually lowers the salinity maximum of NPTW to denser isopycnals. Salinity decrease is especially fast in the MC, with along-path decreasing rate reaching O (10^?7?psu?s^?1). Both diapycnal and isopycnal mixing effects are shown to be elevated in the MC owing to enhanced salinity gradient near the Mindanao Eddy. These results suggest intensive dispersion of thermal anomalies along the subtropical-to-tropical thermocline water pathway near the western boundary.     

利用Argo浮标资料分析横跨吕宋海峡20.5°N断面的水文特征

基于Argo浮标资料,分析了一条横跨南海北部、吕宋海峡和西太平洋（20.5°N,114°~130°E）断面的海水温度、盐度的分布特征.其结果表明：Argo剖面资料得到的2008年秋季20.5°N断面海水的温度、盐度分布态势与气候态秋季的分布基本一致,主要差异在于南海次表层水的盐度极大值和西太平洋次表层水的盐度极大值,2008年秋季二者均比气候态秋季的低0.1左右.通过动力计算（选取1 200 m为速度零面）表明：Argo浮标剖面资料与融合的卫星高度计产品得到的20.5°N,117.5°~124.5°E断面的表层地转流北分量的分布比较吻合;吕宋海峡中部（20°~21°N）的黑潮主轴大致位于121.5°E附近,其东边界可达123°E,而西边界仅限于121°E以西,其可能原因是该季节黑潮的左侧存在着一个气旋式环流,阻碍了黑潮西进;黑潮在20.5°N断面的体积流量为27×106m3/s左右,最大流速约为55 cm/s,出现在70 m层左右.     

应用Argo资料分析西北太平洋冬、夏季水团

应用Argo剖面浮标观测的温、盐度资料,分析了西北太平洋海域冬、夏季的温、盐度分布、水团结构及其分布。首先采用T-S点聚图法分析了该海域水团分布的基本情况,由点聚分析结果可知,该海域至少存在6种以上水团;再用模糊聚类软化法对水团作进一步划分,分别计算了该海域6至11类水团的F和△F值,结果表明,冬、夏季的△F值都以划分为8类时为最大,这与大洋水团的稳定性是一致的,因此,该海域冬、夏季水团以划分为8类最佳,它们分别是北太平洋热带表层水、北太平洋次表层水、北太平洋中层水、北太平洋副热带模态水、北太平洋深层水和赤道表层水,以及南太平洋次表层水和南太平洋中层水。     

应用Argo资料分析西北太平洋冬、夏季水团

应用Argo剖面浮标观测的温、盐度资料,分析了西北太平洋海域冬、夏季的温、盐度分布、水团结构及其分布。首先采用T-S点聚图法分析了该海域水团分布的基本情况,由点聚分析结果可知,该海域至少存在6种以上水团;再用模糊聚类软化法对水团作进一步划分,分别计算了该海域6至11类水团的F和△F值,结果表明,冬、夏季的△F值都以划分为8类时为最大,这与大洋水团的稳定性是一致的,因此,该海域冬、夏季水团以划分为8类最佳,它们分别是北太平洋热带表层水、北太平洋次表层水、北太平洋中层水、北太平洋副热带模态水、北太平洋深层水和赤道表层水,以及南太平洋次表层水和南太平洋中层水。     

Volume transports proceeding to the Kuroshio Extension region and recirculating in the Shikoku Basin

The volume transport of the Kuroshio, the western boundary current of the North Pacific subtropical gyre, varies vigorously due to merging of disturbances propagating from the entire North Pacific. Taking into account the recirculation in the Shikoku Basin by the zonal observation line at 30°N to the west of the Izu–Ogasawara Ridge, we estimated the volume transport in the top 1,000 m layer toward the Kuroshio Extension region. The volume transport of the local recirculation gyre in the Shikoku Basin increases associated with the westward extension of the gyre, particularly in the period of the large meandering path of the Kuroshio south of Japan. Meanwhile, most of the transport variations toward the Kuroshio Extension region correspond to those of the Kuroshio transport on the continental slope south of Japan, which vary independently of those of the recirculation gyre.     

Decadal variations of the North Pacific Tropical Water at 137°E

The decadal variations of the North Pacifi c Tropical Water (NPTW) at 137°E in the western North Pacific Ocean are investigated based on the repeated hydrographic observations along with two global gridded ocean products. The results indicate that the maximum salinity of NPTW experiences signifi cant quasi-decadal variations, having maxima around 1979, 1987, 1995, 2004, and 2012, while minima around 1974, 1983, 1991, 1999, and 2008 during the period of interest. The NPTW area also shows similar quasidecadal variation, expanding/shrinking as its maximum salinity increases/decreases at the 137°E section. These variations are induced mainly by changes in the mixed layer salinity in the source region and largescale circulation in the northwestern tropical Pacific Ocean, both of which are related to the Pacific Decadal Oscillation. The underlying processes at work are further confi rmed through conducting the subsurface salinity budget analysis. Besides, short-term processes are also at work through nonlinear interactions, especially after 2000.     

基于Argo资料的吕宋岛以东海域水团特征分析

基于中国Argo实时资料中心发布的2004年1月至2017年12月Argo全球温盐资料,运用直线定位法和隶属关系,对吕宋岛以东海域(120°～140°E,10°～30°N)水团进行分析,划分出北太平洋次表层水团(NPSSW)和北太平洋中层水团(NPIW)的分布范围.次表层水团位于50～220 m深度,分布在10°～28...     

北太平洋中尺度涡时空特征分析

利用1993~2011年19 a的AVISO卫星高度计资料研究了北太平洋(10°~60°N,120°E~100°W)中尺度涡的时空分布特征,结果表明:北太平洋每年约产生1 800余个涡旋,其中气旋涡稍多。北太平洋东部沿岸、西北沿岸、黑潮延伸体北侧、副热带逆流区是中尺度涡的高发区,春、冬季是涡旋的高发季节。涡极性分布以35°N为界,北部多反气旋涡,南部多气旋涡。涡旋半径以100 km左右为主,并且基本随纬度升高而减小,涡旋数量随着周期增长而急剧下降。反气旋涡的平均半径和周期均大于气旋涡。利用Argo浮标剖面资料分析的6个个例涡旋的垂直结构显示,每个涡旋都有其独特的冷暖核结构,深度不同。研究结果对于分析北太平洋涡动能分布及传输具有一定的参考价值。     

环南澳大利亚太平洋-印度洋海洋间南极中层水环流

On the basis of the salinity distribution of isopycnal(σ_0=27.2 kg/m~3) surface and in salinity minimum, the Antarctic Intermediate Water(AAIW) around South Australia can be classified into five types corresponding to five regions by using in situ CTD observations. Type 1 is the Tasman AAIW, which has consistent hydrographic properties in the South Coral Sea and the North Tasman Sea. Type 2 is the Southern Ocean(SO) AAIW, parallel to and extending from the Subantarctic Front with the freshest and coldest AAIW in the study area. Type 3 is a transition between Type 1 and Type 2. The AAIW transforms from fresh to saline with the latitude declining(equatorward). Type 4, the South Australia AAIW, has relatively uniform AAIW properties due to the semienclosed South Australia Basin. Type 5, the Southeast Indian AAIW, progressively becomes more saline through mixing with the subtropical Indian intermediate water from south to north. In addition to the above hydrographic analysis of AAIW, the newest trajectories of Argo(Array for real-time Geostrophic Oceanography) floats were used to constructed the intermediate(1 000 m water depth) current field, which show the major interocean circulation of AAIW in the study area. Finally, a refined schematic of intermediate circulation shows that several currents get together to complete the connection between the Pacific Ocean and the Indian Ocean. They include the South Equatorial Current and the East Australia Current in the Southwest Pacific Ocean, the Tasman Leakage and the Flinders Current in the South Australia Basin, and the extension of Flinders Current in the southeast Indian Ocean.     

热带中东太平洋海域10°N断面水团分析

本文基于实测温盐数据等资料,利用水团的浓度混合分析等方法,揭示了热带中东太平洋海域10°N断面的水团构成自上而下分别为东部赤道–热带水团、北太平洋中央水团、加利福尼亚流系水团、南太平洋中央水团、太平洋亚北极水团和太平洋深层水团。分析发现,受热带辐合带影响,9°～10°N海域常年持续的正风应力旋度诱发上升流出现,北太平洋中央水团、加利福尼亚流系水团、南太平洋中央水团和太平洋亚北极水团4个通风潜沉水团经向运动至该纬度带时被抽吸至次表层和中层,并散布在不同深度。以往研究仅指出上述4个水团在海表通风形成后将潜沉并向赤道方向运动,本研究进一步阐明了4个水团潜沉后向热带海域运动的动力机制及其在热带中东太平洋10°N断面的散布深度。研究成果揭示了热带中东太平洋水团与北太平洋副热带、亚极地和南太平洋副热带海区中上层水团间的循环过程,对认识北太平洋高–中–低纬度间物质和能量的交换和再分配具有重要科学价值。     

印尼北苏拉威西海蓝碧海峡水团性质的南北差异

Two field observations were conducted around the Lembeh Strait in September 2015 and 2016, respectively.Evidences indicate that seawater around the Lembeh Strait is consisted of North Pacific Tropical Water(NPTW),North Pacific Intermediate Water(NPIW), North Pacific Tropical Intermediate Water(NPTIW) and Antarctic Intermediate Water(AAIW). Around the Lembeh Strait, there exist some north-south differences in terms of water mass properties. NPTIW is only found in the southern Lembeh Strait. Water mass with the salinity of 34.6 is only detected at 200–240 m between NPTW and NPTIW in the southern Lembeh Strait, and results from the process of mixing between the saltier water transported from the South Pacific Ocean and the lighter water from the North Pacific Ocean and Sulawesi Sea. According to the analysis on mixing layer depth, it is indicated that there exists an onshore surface current in the northern Lembeh Strait and the surface current in the Lembeh Strait is southward.These dramatic differences of water masses demonstrate that the less water exchange has been occurred between the north and south of Lembeh Strait. In 2015, the positive wind stress curl covering the northern Lembeh Strait induces the shoaling of thermocline and deepening of NPIW, which show that the north-south difference of airsea system is possible of inducing north-south differences of seawater properties.     

Intermediate Circulation in the Northwestern North Pacific Derived from Subsurface Floats

In order to examine the formation, distribution and synoptic scale circulation structure of North Pacific Intermediate Water (NPIW), 21 subsurface floats were deployed in the sea east of Japan. A Eulerian image of the intermediate layer (density range: 26.6–27.0σ_θ) circulation in the northwestern North Pacific was obtained by the combined analysis of the movements of the subsurface floats in the period from May 1998 to November 2002 and historical hydrographic observations. The intermediate flow field derived from the floats showed stronger flow speeds in general than that of geostrophic flow field calculated from historical hydrographic observations. In the intermediate layer, 8 Sv (1 Sv ≡ 10⁶ m³s⁻¹) Oyashio and Kuroshio waters are found flowing into the sea east of Japan. Three strong eastward flows are seen in the region from 150°E to 170°E, the first two flows are considered as the Subarctic Current and the Kuroshio Extension or the North Pacific Current. Both volume transports are estimated as 5.5 Sv. The third one flows along the Subarctic Boundary with a volume transport of 5 Sv. Water mass analysis indicates that the intermediate flow of the Subarctic Current consists of 4 Sv Oyashio water and 1.5 Sv Kuroshio water. The intermediate North Pacific Current consists of 2 Sv Oyashio water and 3.5 Sv Kuroshio water. The intermediate flow along the Subarctic Boundary contains 2 Sv Oyashio water and 3 Sv Kuroshio water. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于Argo浮标和历史资料的热带西太平洋次表层与中层水年代变化分析

利用20世纪80年代和90年代WOD01(World Ocean Database2001)中的CTD温盐剖面资料和2000年以后Argo资料,对比分析了热带西太平洋次表层和中层水团分布的年代变化特征。分析结果表明,在这两个时期,起源于南北太平洋中高纬度海域的各次表层水和中层水,在热带西太平洋分布特征和交织在一起的总体态势基本一致,水团性质的年代变化不大。这与上述两个时段全球海洋-大气耦合系统趋于正常状态相吻合。通过辨识和跟踪表征次表层水性质的盐度极大值,发现南太平洋热带水沿西边界向北扩散程度有所加大,由前一时期的5°N,进一步扩散到6°~7°N;北太平洋热带水在西边界附近的向南扩散程度有所削弱,在2002-2005年间只向南扩散到4°N,而前一个时期则可向南扩散到2°N。通过辨识表征中层水性质的盐度极小值,南极中层水在西边界附近向北扩散程度有所加大,在2002-2005年到达13°N附近,而前一个时期只到达11°N;同期,北太平洋中层水在西边界附近的向南扩散程度有所削弱。上述年代变化与全球水循环强度的变化之间有何关系有待进一步研究。     

Direct measurements of mid-depth circulation in the Shikoku basin by tracking SOFAR floats

Mid-depth circulation of the Shikoku Basin was measured by tracking four SOFAR floats drifting at the 1,500 m layer. Two floats were released on 17 April 1988 at 30°N, 135°59E and tracked for 433 days. Another two were released on 3 November 1988 at 29°52N and 133°25E, and tracked for 234 days. Two floats flowed clockwise around the Shikoku Warm Water Mass with a diameter of 400 km centered at 31°N and 136°E and a mean drift speed of 4.5 cm sec^–1. One of the floats showed about ten counterclockwise rotations with a period of about 8 days and a maximum speed of 80 cm sec^–1 in the sea area west to the Izu Ridge. In the east to Kyushu, a southward flow was observed under the northward flowing Kuroshio. The southward flow of 4 cm sec^–1 drift speed was considered to be a part of the counterclockwise circulation at deep layers along the perimeter of the Shikoku Basin. One float remained for 234 days in a limited area of 100 km by 150 km in the western part of the basin.     

Further evidence for non-reemergence of winter SST anomalies in the North Pacific eastern subtropical mode water area

Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found: a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper portion.     

北太平洋热带水体积的年际变化及其变化机制

利用EN4(the UK Met Office EN4.2.1 analyses)盐度数据发现北太平洋副热带高盐中心——北太平洋热带水(NPTW)的海表面积与体积在2000—2008年、2014—2017年存在下降趋势,2008—2014年期间存在上升趋势,进一步的研究表明,这些变化与太平洋年代际震荡(PDO)的位相转换紧密相关。利用淡水通量数据以及ECCO2(Circulation and Climate of the Ocean, Phase II)流场数据计算分析后表明,淡水通量对NPTW的变化贡献较小,而水平输运对NPTW的表面积以及体积变化贡献较大,这与PDO正(负)位相期间北赤道流(NEC)的向北(南)摆动有关。     

Origins and pathways of the subsurface and intermediate water masses of the Indonesian Throughflow derived from historical and Argo data

On the basis of Argo data and historic temperature/salinity data from the World Ocean Database 2001 （ WOD01 ）, origins and spreading pathways of the subsurface and intermediate water masses in the Indonesian Throughflow （ITF） region were discussed by analyzing distributions of salinity on representative isopyenal layers. Results were shown that, subsurface water mostly comes from the North Pacific Ocean while the intermediate water originates from both the North and South Pacific Ocean, even possibly from the Indian Ocean. Spreading through the Sulawesi Sea, the Makassar Strait, and file Flores Sea, the North Pacific subsurface water and the North Pacific Intermediate water dominate the western part of the Indonesian Archipelago. Furthermore as the depth increases, the features of the North Pacific sourced water masses become more obvious. In the eastern part of the waters, high sa- linity South Pacific subsurface water is blocked by a strong salinity front between Halmahera and New Guinea. Intermediate water in the eastern interior region owns salinity higher than the North Pacific intermediate water and the antarctic intermediate water （ AAIW）, possibly coming from the vertical mixing between subsurface water and the AAIW from the Pacific Ocean, and possibly coming from the northward extending of the AAIW from the Indian Ocean as well.     

关于黑潮延伸体海域水体的三维热结构时-空变化特征研究

基于西北太平洋Argo数据资料,利用参数化方法,从Argo温盐剖面数据中提取出一系列特征动力参数,定量分析黑潮延伸体海域水体的三维热结构的时-空变化特征、季节变化特征及其与地形和环流的关系.结果表明:黑潮延伸体海域水体的海表面温度存在着明显的冬春弱,夏秋强的季节变化特征,冬季平均海表面温度为15℃,夏季则达到了27℃;...     

137°E断面北赤道流、黑潮变异和黑潮大弯曲的关系

分析了１９７２～１９８８年１３７Ｅ断面资料,结果表明,北赤道流和黑潮、黑潮 和黑潮逆流、北赤道流和热带水以及黑潮、黑潮逆流和亚热带水等,都有０．０１以上 显著水平相关。黑潮既受制于西太平洋大尺度海洋环流,还受大暖涡变化的影响。 北赤道流递减率反应了亚热带环流西部的辐合状况,它的变化是导致日本以南大 暖涡迁移,黑潮路径变化、停滞的主要原因。     

北太平洋西边界流研究综述

综述了近20年来国内外学者在研究北太平洋西边界流的平均结构及NEC分叉动力机制、NM K流系平均输运的分配及变化、NM K流系季节及年际变化规律及其与EN SO之间的关系、NM K流系在热带和亚热带水交换中的作用以及水团的平均分布特征等方面所取得的主要成果。通过分析,发现东亚季风、R ossby波和K e lv in波等是影响北太平洋西边界流的主要因素;而缺乏长期直接的海流观测资料是深入研究北太平洋西边界流遇到的最大障碍。