Effects of the Anticyclonic Eddies on Water Masses, Chemical Parameters and Chlorophyll Distributions in the Oyashio Current Region

Data from the R/V Mirai cruise (May–June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics direct affect the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air pCO₂ difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate show that the anticylonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and DIC between the upper (σ_θ = 26.7–27.0) and lower (σ_θ = 27.1–27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quasiperiodic small meanders of the Kuroshio off Cape Ashizuri and their inter-annual modulation caused by quasiperiodic arrivals of mesoscale eddies

A quasiperiodic variation of 100–110 days in the Kuroshio path off Cape Ashizuri, resulting from the passage of small meanders, was detected by observation with moored current meters during 1993–1995. TOPEX/POSEIDON altimeter data covering 9 years showed that the quasiperiodic variation period was not persistent and modulated twice, with a ∼110-day period from mid-1993 to late 1996, a ∼150-day period from late 1996 to mid-1999, and a ∼110-day period from mid-1999 to late 2001. The quasiperiodic variations of the Kuroshio path migration were contemporaneous with the quasiperiodic arrivals of mesoscale eddies from the east along 27–32°N over the same ∼110- and ∼150-day period quasiperiodic variations. The periodic arrivals of the eddies configure the periodic variations of the Kuroshio path and its inter-annual modulation.     

Zooplankton Distribution and Dynamics in a North Pacific Eddy of Coastal Origin: I. Transport and Loss of Continental Margin Species

Zooplankton from coastal/continental margin environments can be transported long distances seaward into the subarctic North Pacific by the large (100–200 km diameter) anticyclonic eddies that form annually in late winter along the eastern margin of the Alaska Gyre. One recurrent region for eddy formation is off the southern tip of the Queen Charlotte Islands (near 52°N 132°W). Eddies from this source region (termed ‘Haida eddies’) propagate westward into open ocean waters during the subsequent 1–3 years, often to about 140°W, occasionally to mid gyre. Each eddy contains a core of anomalously low density water, and produces an upward doming of the sea surface detectable by satellite altimetry, thereby aiding repeated ship-based sampling. The zooplankton community in the eddies is a mixture between shelf/slope species (transported from the nearshore formation region) and subarctic oceanic species (which colonize the eddy from the sides and below). This paper reports sequential observations (late winter, early summer and fall seasons of 2000, and early summer and fall of 2001) of the abundance and distribution of continental-margin zooplankton in the Haida eddies that formed in late winters of 2000 and 2001. Shelf-origin species declined in abundance over time. Species that appeared to have a continental slope origin sometimes declined but sometimes persisted and flourished. Transport and retention within the eddy appeared to be especially effective for species that undergo diel vertical migration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Drifter Observations of Anticyclonic Eddies near Bussol' Strait, the Kuril Islands

Hydrographic surveys and satellite imaging reveal that mesoscale anticyclonic (AC) eddies are common features of the area south of Bussol' Strait, the deepest of the Kuril straits connecting the western North Pacific and Sea of Okhotsk. To examine the velocity structure of these eddies, we deployed groups of 15-m drogued satellite-tracked surface drifters over the Kuril-Kamchatka Trench in the fall of 1990 and late summer of 1993. Drifters in both groups entered large AC eddies centered over the axis of the trench seaward of Bussol' Strait and subsequently underwent a slow northeastward translation. One drifter (Drifter 1315) deployed near the center of the “Bussol' eddy” in 1990, remained in the eddy for roughly 45 days and made five loops at successively greater distances from the eddy center. Large-amplitude (80–100 cm/s) storm-generated inertial oscillations were observed during the first two loops. The vorticity field associated with the eddy resulted in a Doppler “red-shift” of inertial frequency motions such that the “effective” inertial period of 21 hours was roughly 4 hours greater than the nominal inertial period for the drifter latitude (45°N). In 1993, a second drifter (Drifter 15371) was retained in the Bussol' eddy for about 40 days. This eddy had characteristics similar to those of the 1990 eddy but was devoid of significant high-frequency motions until the drifter's final half loop. The observed spatial scales, persistence, and slow poleward translation of the eddies suggests that they play an important role in the dynamics of the East Kamchatka and Oyashio current systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific

Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic (cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting that these eddies are important in the formation of mode waters, particularly L-CMW.     

Statistics of mesoscale cyclonic Eddies over the Black Sea

On the basis of the results obtained by using the PRECIS regional climate model with high space resolution (25 km), we study the mesoscale specific features of the atmospheric circulation in the Black-Sea region for a period of 30 yr. To separate and trace the subsynoptic eddies, we use a method based on the Okubo–Weiss criterion. Several types of cyclonic eddies are selected and described: winter Caucasian coastal eddies, summer Caucasian separated eddies, cyclonic eddies of the open sea, and seldom quasitropical cyclones. For various types of eddies, we present the statistics of their lifetime and intensity and the histograms of diurnal and seasonal cycles.     

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 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。     

Anticyclonic eddies in the Norwegian Sea; their generation,evolution and impact on primary production

Altimetry and ocean color observations are used in combination with a coupled physical-primary production ocean model to investigate anticyclonic eddies at two locations in the Norwegian Sea. Of particular interest are the formation of the anticyclonic eddies, and their influence on primary production. The formation of these anticyclonic eddies are due to baroclinic instabilities set up by shifts in the wind in north/south direction, leading to simultaneously formation of eddies throughout the area. After a density stratification develops in the upper 100 m of the water column, the anticyclones become a subsurface lens of well mixed water with the characteristics of intra-thermocline eddies. The deep mixed layer inside anticyclonic eddies delay phytoplankton bloom by approximately two weeks compared to the surrounding areas. As the mixed layer within the anticyclones become smaller than the critical depth, the combination of this and sufficiently high nutrient levels support a phytoplankton bloom. From the satellite observations, there is an evidence of phytoplankton being advected toward the center of the eddies, but also of isolated phytoplankton blooms within the intra-thermocline eddies. The combined use of a numerical model and satellite observations provides three-dimensional information on the structure and properties of both eddies and primary production. The presented model is particularly useful in cloud-covered areas where ocean color images are frequently unavailable.     

黑潮延伸体邻近区域中尺度涡特征统计分析

本文利用20年的卫星高度计资料,对黑潮延伸体邻近海区(25°—45°N,135°E—175°W)中尺度涡的统计特征以及季节变化进行了统计研究。基于涡旋自动识别方法,共识别出本区域3006个气旋涡轨迹和2887个反气旋涡轨迹,其平均周期分别为9.99周和11.00周,平均半径分别为69.5km和71.8km。长生命周期涡旋的平均半径、涡度、涡动能(EKE)和涡旋能量密度(EI)在生命周期内大致都经历了增大-基本保持不变-减小这三个阶段。绝大多数涡旋沿纬线向西移动,经向移动距离较小,气旋涡和反气旋涡在西向传播过程中都具有明显的向南(赤道)偏离趋势。涡旋的生成数量与总数量均在春夏季达到最多,且这一时期涡旋的平均涡度、EKE、EI处于较高水平。     

Hawaii Cyclonic Eddies and Blue Marlin Catches: The Case Study of the 1995 Hawaiian International Billfish Tournament

The combination of prevailing northeasterly tradewinds and island topography results in the formation of vigorous, westward propagating cyclonic eddies in the lee of the Hawaiian Islands on time scales of 50–70 days. These mesoscale (∼10² km) features are nowhere more conspicuous or spin up more frequently than in the Alenuihaha Channel between the Island of Maui and the Big Island of Hawaii. Cyclonic eddies in subtropical waters such as those around Hawaii vertically displace the underlying nutricline into the overlying, nutrient-depleted euphotic zone creating localized biologically enhanced patches. Insight into how these eddies may directly influence pelagic fish distribution is provided by examination of recreational fish catch data coinciding with the presence of eddies on the fishing grounds. We highlight the 1995 Hawaii International Billfish Tournament in which a cyclonic eddy dominated the ocean conditions during the weeklong event and the fish catch distribution differed significantly from the average historical tournament catch patterns. On the tournament fishing grounds, well-mixed surface layers and strong current flows induced by the eddy's presence characterized the inshore waters where the highest catches of the prized Pacific blue marlin (Makaira mazara) occurred, suggesting possible direct (e.g., physiological limitations) or indirect (e.g., prey availability) biological responses of blue marlin to the prevailing environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

The concept of tidal exchange and the tidal exchange ratio

The principal character of the tidal exchange process is neither diffusion nor advection, but a third category of transport, “Massenaustausch”, which appears in the space/time averaged transport. The exchange process can be divided into four fluxes: the flux of standing eddies, the flux of tidal exchange, the flux of tidal eddies and the flux of local eddies. The results of observations at the entrance channel of Kumihama-Bay show a typical example of transport dominated by tidal exchange. The tidal exchange ratio defined by Parkeret al. (1972) applies to the process of exchange between the outflowing watermass and the surrounding watermass outside of the bay mouth, but this should also be considered as being coupled with the ratio for the process of exchange between the inflowing watermass and the surrounding watermass inside of the bay mouth. These two exchange ratios can be combined into a single exchange ratio which describes the exchange process between the outer watermass and the bay water.     

Estimation of the long-term variability of hydrophysical characteristics of the Black Sea based on the assimilation of the climatic hydrological fields L and altimetry data

To study the long-term variability of the thermohaline and dynamic characteristics of the Black Sea, we use three versions of climatic fields, namely, the fields reconstructed in the model according to the old (1903–1982) and new (1903–2003) hydrological climatic data arrays of temperature and salinity and according to the data of satellite altimetry. The analysis of the altimetry-based climatic fields confirms the distinctions (established earlier according to the old and new data arrays) in the seasonal variability of the integral characteristics of temperature and salinity and in the structures of hydrophysical fields in the sea. It is shown that, in the winter-spring season, the thermohaline fields reconstructed according to the new and altimetry data arrays are characterized by a small elevation of the halocline (pycnocline) and the upper boundary of the cold intermediate layer. In all seasons, the altimetry-based surface geostrophic currents contain numerous mesoscale eddies with different signs of rotation. Moreover, in all seasons, the Rim Current reconstructed according to the altimetry data is characterized by a narrower jet almost along the entire its length. This jet is especially intense near the coasts of West Anatolia. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 3–17, July–August, 2006.     

Trajectory of Mesoscale Eddies in the Kuroshio Recirculation Region

Trajectories of mesoscale eddies in the Kuroshio recirculation region were investigated by using sea surface height (SSH) anomaly observed by the TOPEX/POSEIDON and ERS altimeters. Cyclonic and anticyclonic eddies have been traced on maps of the filtered SSH anomaly fields composed from the altimeter observations every ten days. Both the cyclonic and anticyclonic eddies propagate westward in the Kuroshio recirculation region from a region south of the Kuroshio Extension. The propagation speed of these eddies has been estimated as about 7 cm s⁻¹, which is much faster than the phase speed theoretically estimated for the baroclinic first-mode Rossby wave in the study area. It was also found that in the Izu-Ogasawara Ridge region, most of eddies pass through the gap between the Hachijojima Island and Ogasawara (Bonin) Islands, and some of the eddies decay around the Izu-Ogasawara Ridge. It seems that the trajectory of the eddies is crucially affected by the bottom topography. In the region south of Shikoku and east of Kyushu, some of the eddies coalesce with the Kuroshio. It is also suggested that this coalescence may trigger the path variation of the Kuroshio in the sea south of Japan. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preliminary results of measurements of atmospheric turbulence over the sea

We perform the experimental verification of the applicability of the theory of similarity to the wave boundary layer and the assessment of wave-induced perturbations of the air flow depending on various conditions of stratification of the atmosphere and the state of the sea. The measurements were carried out from a stationary platform located in the coastal part of the Black Sea. The experimental procedure is based on the simultaneous measurements of the profile and fluctuations of the wind speed at 5–6 levels in the 1.3–21-m layer, the elevations of the sea surface, the directions of waves and winds, and the mean gradients of temperature and humidity of air. The structure of the boundary layer in the region of measurements depends on the direction of the wind. For weak and moderate onshore winds (< 9 m/sec), the approximate balance is preserved between the production and dissipation of turbulent energy in the cases of unstable and neutral stratification. On the average, the estimates of friction velocity according to the profiles are higher than the dissipative estimates by 10% mainly due to the deficiency of dissipation near the surface. For the offshore wind, the structure of the boundary layer abruptly changes and is determined not by the local parameters but by strong turbulent eddies formed over the dry land. The intensity of low-frequency turbulent fluctuations and the gradient of wind velocity near the surface in the coastal zone are 1.5–2 times higher than for the open sea. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 42–61, May–June, 2007.     

Spatial and Temporal Scale Variations of Sea Surface Temperature in the East Sea Using NOAA/AVHRR Data

Sea surface temperature fields in the East Sea are composed of various spatial structures such as eddies, fronts, filaments, turbulent-like features and other mesoscale variations associated with the oceanic circulations of the East Sea. These complex SST structures have many spatial scales and evole with time. Semi-monthly averaged SST distributions based on extensive satellite observations of SSTs from 1990 through 1995 were constructed to examine the characteristics of their spatial and temporal scale variations by using statistical methods of multi-dimensional autocorrelation functions and spectral analysis. Two-dimensional autocorrelation functions in the central part of the East Sea revealed that most of the spatial SST structures are anisotropic in the shape of ellipsoids with minor axes of about 90–290 km and major axes of 100–400 km. Two dimensional spatial scale analysis demonstrated a consistent pattern of seasonal variation that the scales appear small in winter and spring, increase gradually to summer, and then decrease again until the spring of the next year. These structures also show great spatial inhomogeneity and rapid temporal change on time scales as short as a semi-month in some cases. The slopes in spectral energy density spectra of SSTs show characteristics quite similar to horizontal and geostrophic turbulence. Temporal spectra at each latitude are demonstrated by predominant peaks of one and two cycles per year in all regions of the East Sea, implying that SSTs present very strong annual and semi-annual variations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Satellite altimeter observations of nonlinear Rossby eddy–Kuroshio interaction at the Luzon Strait

Satellite altimeter sea level data from 1993 to 2008 are used to analyze the interaction of nonlinear Rossby eddies with the Kuroshio at the Luzon Strait (LS). The sea level anomaly data show that the west Pacific (WP) is a source of nonlinear Rossby eddies, and the South China Sea (SCS) is a sink. The LS serves as a gateway between the two. The scale analysis indicates that eddies with a radius larger than 150 km are strong enough to significantly alter the Kuroshio and are able to modify the local circulation pattern. Statistical analysis indicates that the probability for eddies to penetrate through the Kuroshio may reach at least 60%. A case study of an anticyclonic mesoscale eddy passing through the LS in June–July 2004 indicates that the Kuroshio behaves as an unsteady flow with its stream path frequently modified, in a way of cutting off, meandering and branching during its interaction with the eddy. We therefore suggest that nonlinear Rossby eddies may play a significant role in modification of the local circulation system near the LS and in exchanges of the mass, momentum and energy between the WP and the SCS.     

Low Salinity, Cool-Core Cyclonic Eddy Detected Northwest of Luzon during the South China Sea Monsoon Experiment (SCSMEX) in July 1998

To detect eddies, intensive surveys of the northeast South China Sea (SCS) (114°30′–121°30′ E, 17°–22°N) were conducted in July 1998 during the international SCS Monsoon Experiment (SCSMEX), the U.S. Navy using Airborne Expendable Bathythermograph and Conductivity-Temperature-Depth sensors (AXBT/AXCTD), and the Chinese Academy of Sciences using Acoustic Doppler Current Profilers (ADCP). The hydrographic survey included 307 AXBT and 9 AXCTD stations, distributed uniformly throughout the survey area. The ADCP survey had two sections. The velocity field inverted from the AXBT/AXCTD data and analyzed from the ADCP data confirm the existence of a low salinity, cool-core cyclonic eddy located northwest of Luzon Island (i.e., the Northwest Luzon Eddy). The radius of this eddy is approximately 150 km. The horizontal temperature gradient of the eddy increases with depth from the surface to 100 m and then decreases with depth below 100 m. The cool core was evident from the surface to 300 m depth, being 1°–2°C cooler inside the eddy than outside. The tangential velocity of the eddy is around 30–40 cm/s above 50 m and decreases with depth. At 300 m depth, it becomes less than 5 cm/s. This revised version was published online in August 2006 with corrections to the Cover Date.     

Three dimensional diagnostic modeling study of the South China Sea circulation before onset of summer monsoon in 1998

The wind data from NCEP and hydrographic data obtained from April 22–May 24, 1998 have been used to compute the circulation in the South China Sea (SCS) using three dimensional diagnostic models. The main numerical results with SSHA derived from T/P altimeter are as follows: most of intruded Kuroshio bypasses. However, a part of Kuroshio intrudes westward above 300 m levels. This intruded westward flow is narrowly confined to the continental slope south of China, in agreement with the findings of Qu et al. (2000). The basin-scale cyclonic gyre dominates in the northern SCS and consists of two cyclonic eddies, C2 and C3, above 300 m levels. However, it is separated into two parts by an anti-cyclonic eddy, W4, below 300 m. The basin-scale anti-cyclonic gyre dominates in the central SCS and consists of three anti-cyclonic eddies, W1, W2 and W3, above 300 m levels. However, below 300 m it consists of the anti-cyclonic eddies W1, W2 and W4 and extends northward to near 20°N. A northward coastal jet is present near the coast of Vietnam at depths above 300 m, and develops northward further to about a distance of 3°15′ N than that in cruise 2. The most important dynamical mechanism is due to the joint effect of the baroclinity and relief. The second dynamical mechanism is due to the interaction between the wind stress and relief. The topography effect is more important than the β effect. The Sverdrup relation cannot be satisfied in the SCS.     

短生命周期海洋涡旋的时空分布特征

中尺度涡旋在海洋中分布广泛,是海洋动力、营养物质等混合和输运的重要途径。统计发现海洋中超过80%的涡旋生命周期不超过1个月,属于本文定义的短生命周期涡旋。本研究采用统计、对比等方法,对全球尺度,较短生命周期涡旋的时空分布特征进行了分析。研究表明,短生命周期涡旋与大洋中环流系统密切相关,其最易发生在暖流和寒流的交汇处以及运动方向相反的两种环流的交汇处,且在除30°S～30°N的热带地区外均表现为气旋式略多于反气旋式。低纬地区,短生命周期涡旋在每年的冷季数量较多,而高纬地区与之相反。除存在大规模东向环流的海域,短生命周期涡旋一般向西迁移,同时气旋式涡旋略倾向于赤道偏转,反气旋式略倾向于极地偏转。短生命周期涡旋的平均位移和平均迁移速率呈相似的赤道对称分布规律。