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1.
The characteristics of the Kuroshio axis south of Kyushu, which meanders almost sinusoidally, are clarified in relation to the large meander of the Kuroshio by analyzing water temperature data during 1961–95 and sea level during 1984–95. The shape of the Kuroshio axis south of Kyushu is classified into three categories of small, medium, and large amplitude of meander. The small amplitude category occupies more than a half of the large-meander (LM) period, while the medium amplitude category takes up more than a half of the non-large-meander (NLM) period. Therefore, the amplitude and, in turn, the curvature of the Kuroshio axis is smaller on average during the LM period than the NLM period. The mean Kuroshio axis during the LM period is located farther north at every longitude south of Kyushu than during the NLM period, with a slight difference west of the Tokara Islands and a large difference to the east. A northward shift of the Kuroshio axis in particular east of the Tokara Islands induces small amplitude and curvature of the meandering shape during the LM period. During the NLM period, the meandering shape and position south of Kyushu change little with Kuroshio volume transport. In the LM formation stage, the variation of the Kuroshio axis is small west of the Tokara Islands but large to the east due to a small meander of the Kuroshio. In the LM decay stage, the Kuroshio meanders greatly south of Kyushu and is located stably near the coast southeast of Kyushu. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
This study investigates the long-term variability of the Kuroshio path south of Japan. Sensitivity experiments using a data-assimilative model suggest that the duration of the large meander (LM) strongly depends on the Kuroshio transport; specifically, low transport leads to a long duration of the LM. Actually, we find a good correlation between the duration of the past LMs and the Sverdrup transport estimated by a wind-driven linear baroclinic vorticity model. Then we explore favorable conditions for the LM and find a close relationship between the Kuroshio Extension (KE) state and the LM. That is, a precondition for the LM that the Kuroshio path on the Izu Ridge is fixed at a deep channel located around 34°N is achieved during a stable KE state. In addition, westward propagating signals with negative anomalies in the Kuroshio region and high sea-surface height (SSH) state east of Taiwan are key for generation of a small meander southeast of Kyushu that triggers a subsequent LM. The signals related to the above conditions change the upstream Kuroshio transport and velocity, which are consistent with features indicated by the former observational studies. Using reanalysis data, we construct long-time series of indices for the three conditions, which explain well the past LMs. The indices suggest that long-term non-LM states around 1970 and in the 1990s were attributed to a low-SSH state east of Taiwan and an unstable KE state, respectively.  相似文献   

3.
The influence of the Kuroshio flow on the horizontal distribution of North Pacific Intermediate Water (NPIW) in the Shikoku Basin is examined based upon observational data collected by the training vessel “Seisui-maru” of Mie University together with oceanographic data compiled by the Japan Oceanographic Data Center (JODC). Although it has been stated that the NPIW with salinity less than 34.2 psu had been confined to the south of the Kuroshio main axis along the PT (KJ) Line on the eastern side of the Izu Ridge, a similar tendency can be detected on the western side of the Izu Ridge. Namely, the NPIW on the southern side of the Kuroshio main axis in the Shihoku Basin does not indicate a tendency to go northward across the Kuroshio main axis without an increase in salinity of more than 34.2 psu. However, the JODC data show that less saline water (<34.2 psu) was present on the northern side of the Kuroshio main axis south of the Kii Peninsula in May 1992. Satellite observed sea surface temperature (SST) data suggested that the Kuroshio approaches the Kii Peninsula after forming a small meander off Kyushu and some intrusions of the NPIW into the northern coastal side of the Kuroshio main axis occurred in this period. It is concluded that intrusion of the NPIW with salinity less than 34.2 psu to the northern coastal side through the Kuroshio main axis occurred during the decay period of the small meander path in May 1992. Based on these observational results, the source of the salinity minimum water on the northern coastal side of the Kuroshio main axis is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
A high-resolution ocean model forced with an annually repeating atmosphere is used to examine variability of the Kuroshio, the western boundary current in the North Pacific Ocean. A large meander (LM) in the path of the Kuroshio south of Japan develops and disappears in a highly bimodal fashion on decadal timescales. The modeled meander is comparable in timing and spatial extent to an observed feature in the region. Various characteristics of the LM are examined, including relative vorticity, transport, and velocity shear. The many similarities between the model and observations indicate that the meander results from intrinsic oceanic variability, which is represented in this climatologically forced model. Each LM is preceded by a smaller “trigger” meander that originates at the south end of Kyushu, moves up the coast, and develops into the LM. However, there are also many meanders very similar in character to the trigger meander that do not develop into LMs. Formation of an LM only occurs when a deep anticyclone associated with the trigger meander forms near Koshu Seamount. Furthermore, the major axis of that deep anticyclone must be oriented away from the coast, rather than alongshore. In the specific case of interaction of a trigger meander with a deep anticyclone with major axis oriented away from the coastline, LM formation occurs.  相似文献   

5.
The occurrence of the small meander of the Kuroshio, generated south of Kyushu and propagating eastward, was examined using sea level data collected during 1961–1995 along the south coast of Japan. Intra-annual variation of the sea level was expanded by the frequency domain empirical orthogonal function (FDEOF) modes, and it was found that the second and third modes are useful for monitoring the generation and propagation of the small meander. The third FDEOF for periods of 10–100 days has a phase reversal between Hosojima and Tosa-shimizu with significant amplitude west of Kushimoto, and the amplitude of its time coefficient is large during the non-large-meander (NLM) period and has a significant peak when the small meander exists southeast of Kyushu. The second FDEOF for periods of 20–80 days has a phase reversal between Kushimoto and Uragami, and the amplitude of its time coefficient is large when the small meander propagates to the south of Shikoku. The third FDEOF mode allowed us to conclude that the small meander occurred 42 times from July 1961 to May 1995, most of them (38) occurring during the NLM periods. The second FDEOF mode permits the conclusion that half of the 38 small meanders reached south of Shikoku. Of these, five small meanders influenced transitions of the Kuroshio path from the nearshore NLM path; one caused the offshore NLM path and four brought about the large meander. About one-tenth of the total number of small meanders are related to the formation of the large meander.  相似文献   

6.
The coastal sea level propagating westward along the south coast of Japan and the impact of the disturbance on the generation of the Kuroshio small meander have been examined. The propagation occurs in sea level variations for periods shorter than 10 days and is remarkable for periods of 4–6 days. Characteristics of the 4–6 day component have been studied using the extended empirical orthogonal function (EEOF). The first and second modes of EEOF are almost in-phase throughout the south coast of Japan. The higher four modes of EEOF are significantly excited when the Kuroshio takes the non-large-meander path, and propagate westward with phase speeds of 2.8 m s−1 (third and fourth modes) and 1.6 m s−1 (fifth and sixth modes) in the Kuroshio region west of Mera in the Boso Peninsula. The analysis shows that more than 70% of the small meanders generate in two months after a significant propagating disturbance reaches south of Kyushu when the velocity of the Kuroshio is high. This effect of coastal disturbance is examined by numerical experiments with a 2.5-layer model in which coastal disturbance is excited by vertical displacement of the upper interface. The result is that offshore displacement of the Kuroshio occurs southeast of Kyushu only in the case of significant upward displacement of the interface under the influence of a high Kuroshio velocity. The significant coastal disturbance, which is associated with upward displacement of the density interface, and a high Kuroshio velocity can therefore be important factors in generating small meanders.  相似文献   

7.

Since September 2017, the Kuroshio has taken a large-meander (LM) path in the region south of Japan. We examined characteristics of the 2017–present LM path in comparison with previous LM paths, using tide gauge, altimetric sea surface height, and bottom pressure data. The 2017–present LM path was formed from a path passing through a channel south of Hachijo-jima Island, while a typical LM path originated from a path through a channel north of Miyake-jima Island. The meander trough of this atypical path was found to be shifted far to the east and to vary on a timescale of months. These characteristics are different from those of a typical LM path but they are similar to those of the 1981–1984 LM path. Therefore, we identified two types of LM path; a stable and unstable LM paths. The 2017–present unstable type large meander has a zonal scale greater than that of the 2004–2005 stable type large meander and protrudes from the eastern boundary of the Shikoku Basin, i.e., Izu-Ogasawara Ridge. No significant bottom pressure depression was observed, associated with the formation of the 2017–present LM path, indicating that baroclinic instability was not important in the formation of this LM path. Due to no significant bottom steering, even during the 2017–present LM period, a mesoscale current path disturbance occurred southeast of Kyushu, propagated eastward, and amplified the offshore displacement of the Kuroshio.

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8.
Current path records of the Kuroshio off southern Japan have been examined for the period 1960–1977. Together with previously published results (S.Yoshida, 1961;Shoji, 1972) this evidence indicates that all major changes in the path of the Kuroshio off Cape Shiono were preceded by the formation of a small trigger meander off Kyushu and its downstream propagation to Cape Shiono. The periods of occurrence of these trigger meanders, most of which decay without propagating downstream, are documented. Small meanders off Kyushu occur throughout the year, but all of those which triggered changes off Cape Shiono were initially generated in the period January–April.Contribution No. 4 of the Pacific International Research Association.  相似文献   

9.
The processes underlying the development of the Kuroshio large meanders that occurred in 1986 and 1989 are investigated using a satellite SST data set and hydrographic data. In both processes visible on the satellite SST images, a round-shaped, lower SST region with a diameter of about 200 km is found to the east of the Kuroshio small “trigger” meander (Solomon, 1978) until the region became extinguished near theEnshu Nada. The lower SST region can be interpreted as an anti cyclonic eddy, mainly because of the existence of a warm water mass in the subsurface layer of this region. The warm water mass is characterized by a constant temperature of 18–19°C, the maximum thickness of which is about 400 m. The satellite images show that the eddy is closely related to the Kuroshio path transforming into a shape like the letter “S”. This means that the eddy plays an important role in the development of the Kuroshio large meander since this, too, tends to follow an “S”-shaped path. Added to this, the subsurface layer structure of the eddy is similar to that of the warm water mass offShikoku. This similarity, together with the eddy behavior visible on the satellite SST images, implies that the examined eddy corresponds to the warm water mass offShikoku. In other words, the warm water mass offShikoku can be advected near to theEnshu Nada when the Kuroshio large meander occurs.  相似文献   

10.
Conditions for the formation of large meander (LM) of the Kuroshio are inferred from observational data, mainly obtained in the 1990s. Propagation of the small meander of the Kuroshio from south of Kyushu to Cape Shiono-misaki is a prerequisite for LM formation, and three more conditions must be satisfied. (1) The cold eddy carried by small meander interacts with the cold eddy in Enshu-nada east of the cape. During and just after the propagation of small meander, (2) the Kuroshio axis in the Tokara Strait maintains the northern position and small curvature, and (3) current velocity of the Kuroshio is not quite small. If the first condition is not satisfied, the Kuroshio path changes little. If the first condition is satisfied, but the second or third one is not, the Kuroshio transforms to the offshore non-large-meander path, not the LM path. All three conditions must be satisfied to form the large meander. For continuance of the large meander, the Kuroshio must maintain the small curvature of current axis in the Tokara Strait and a medium or large range of velocity and transport. These conditions for formation and continuance may be necessary for the large meander to occur. Moreover, effects of bottom topography on position and structure of the Kuroshio are described. Due to topography, the Kuroshio changes horizontal curvature and vertical inclination of current axis in the Tokara Strait, and is confined into either of two passages over the Izu Ridge at mid-depth. The former contributes to the second condition for the LM formation.  相似文献   

11.
The influences of mesoscale eddies on variations of the Kuroshio path south of Japan have been investigated using time series of the Kuroshio axis location and altimeter-derived sea surface height maps for a period of seven years from 1993 to 1999, when the Kuroshio followed its non-large meander path. It was found that both the cyclonic and anticyclonic eddies may interact with the Kuroshio and trigger short-term meanders of the Kuroshio path, although not all eddies that approached or collided with the Kuroshio formed meanders. An anticyclonic eddy that revolves clockwise in a region south of Shikoku and Cape Shionomisaki with a period of about 5–6 months was found to propagate westward along about 30°N and collide with the Kuroshio in the east of Kyushu or south of Shikoku. This collision sometimes triggers meanders which propagate over the whole region south of Japan. The eddy was advected downstream, generating a meander on the downstream side to the east of Cape Shionomisaki. After the eddy passed Cape Shionomisaki, it detached from the Kuroshio and started to move westward again. Sometimes the eddy merges with other anticyclonic eddies traveling from the east. Coalescence of cyclonic eddies, which are also generated in the Kuroshio Extension region and propagate westward in the Kuroshio recirculation region south of Japan, into the Kuroshio in the east of Kyushu, also triggers meanders which mainly propagate only in a region west of Cape Shionomisaki. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
Properties of the index of position of the Kuroshio axis in the Tokara Strait, named the Kuroshio position index (KPI), were examined using sea-level data during 1984–92. The index is KPI=(X+M x )/(Y+M y whereX(Y) is the anomaly of sea-level difference of Nakanoshima (Naze) minus Nishinoomote from the 1984–92 meanM x (M y ). The correlation with the latitude of the Kuroshio axis in the Tokara Strait concluded that the KPI withM x /M y =0.83 and realisticM y (100±40 cm) best indicates the position of the Kuroshio axis in the strait. The KPI withM x =83 cm andM y =100 cm was newly called the KPI as the best index. Using daily values of this KPI, the relation between the position of the Kuroshio in the strait and the large meander of the Kuroshio shown by Kawabe (1995) was confirmed and studied in detail. A large meander forms (ends) 3.3 (5.1) months after a northward (southward) shift of the Kuroshio in the Tokara Strait. Yet, a temporary southward shift with a duration of ten to twenty days does not finish the large-meander (LM) path. At the LM formation, a small meander southeast of Kyushu begins to move eastward associated with the northward shift. The processes of LM formation and decay are started by the meridional move of the Kuroshio axis in the Tokara Strait. The Kuroshio axis at the FES line during the LM path is located farther north by 7 latitude than that during the non-large-meander (NLM) path. The latitude during the LM formation (decay) stage is a little higher (lower) than that during the LM (NLM) period, though the Kuroshio still takes an NLM (LM) path.  相似文献   

13.
The generation of small meanders of the Kuroshio south of Kyushu has been investigated using a high-resolution ocean general circulation model of the North Pacific Ocean. The small cyclonic meander develops in the region east of the Tokara Strait with a period of about one month, then propagates downstream along the Kuroshio path to the longitude of the Kii Peninsula, which is similar to the so-called trigger meanders for the formation of the large-meander of the Kuroshio south of Japan. It turns out that the generation of the small meander is a local phenomenon, strongly associated with anticyclonic eddies that propagate northeastward along the Kuroshio path in the East China Sea. The vorticity balance indicates that the accumulation of positive vorticity during the developing phase of the small meander occurs mainly from the balance between the stretching and the advection terms. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
An inverse calculation using hydrographic section data collected from October to December 2000 yields velocity structure and transports of the Kuroshio in the Okinawa Trough region of the East China Sea (ECS) and south of central Japan, and of the Ryukyu Current (RC) southeast of the Ryukyu Islands. The results show the Kuroshio flowing from the ECS, through the Tokara Strait (TK), with a subsurface maximum velocity of 89 cm s−1 at 460 dbar. In a section (TI) southeast of Kyushu, a subsurface maximum velocity of 92 cm s−1 at 250 dbar is found. The results also show the RC flowing over the continental slope from the region southeast of Okinawa (OS) to the region east of Amami-Ohshima (AE) with a subsurface maximum velocity of 67 cm s−1 at 400 dbar, before joining the Kuroshio southeast of Kyushu (TI). The volume transport around the subsurface velocity maximum southeast of Kyushu (TI) balances well with the sum of those in TK and AE. The temperature-salinity relationships found around these velocity cores are very similar, indicating that the same water mass is involved. These results help demonstrate the joining of the RC with the Kuroshio southeast of Kyushu. The net volume transport of the Kuroshio south of central Japan is estimated to be 64∼79 Sv (1 Sv ≡ 106 m3s−1), of which 27 Sv are supplied by the Kuroshio from the ECS and 13 Sv are supplied by the RC from OS. The balance (about 24∼39 Sv) is presumably supplied by the Kuroshio recirculation south of Shikoku, Japan.  相似文献   

15.
Sea level variations from 1974 through 1976 at 9 stations on the south coast of Japan (from west to east, Aburatsu, Tosa-shimizu, Muroto-misaki, Kushimoto, Uragami, Owase, Toba, Maisaka and Omaezaki) were analysed in relation to the large meander in the Kuroshio. From May to July in 1975, a small maximum in sea level variation was observed at every station west of Cape Shionomisaki from Aburatsu to Kushimoto. It propagated eastward along with the eastward propagation of a small meander in the Kuroshio until it reached Kushimoto, when the sea levels at Uragami and Owase started to rise sharply. This remarkable rise appeared at all stations in August when a large meander in the Kuroshio was established. The mean sea level at the stations east of Cape Shionomisaki from Uragami to Omaezaki rose by about 10 cm. The difference in sea level variations between the regions east and west of Cape Shionomisaki, which had been present before the rise, disappeared. A similar characteristic of sea level variation was also found in the generation stage of the large meander in 1959. The sea level variations along the south coast of Japan indicate that, prior to the generation of the large meander, the small meander in the Kuroshio was generated southeast of Kyushu and propagated eastward and that, just when this meander reached off Cape Shionomisaki, a large scale oceanic event covering over the whole region of the south coast of Japan occurred. This large scale event seems to be one of the necessary conditions for the generation of the large meander in the Kuroshio off Enshû-nada.  相似文献   

16.
We examine the processes underlying the generation and propagation of the small meander of the Kuroshio south of Japan which occurs prior to the transition from the non-large meander path to the large meander path. The study proceeds numerically by using a two-layer, flat-bottom, quasi-geostrophic inflow-outflow model which takes account of the coastal geometries of Kyushu, Nansei Islands, part of the East China Sea, and the Izu Ridge. The model successfully reproduces the observed generation and propagation features of what is called "trigger meander" until it passes by Cape Shiono-misaki; presumably because of the absence of the bottom topography, the applicability of the present numerical model becomes questionable after the trigger meander passes by Cape Shiono-misaki. The generation of the trigger meander off the south-eastern coast of Kyushu is shown to be associated with the increase in the supply of cyclonic vorticity by the enhanced current velocity in the upper layer along the southern coast of Kyushu where the no-slip boundary condition is employed. Thereafter, the trigger meander propagates eastward while inducing an anticyclone-cyclone-cyclone pair in the lower layer. The lower-layer cyclone induced in this way, in particular, plays a crucial role in intensifying the trigger meander trough via cross-stream advection in the upper layer; the intensified trigger meander trough then further amplifies the lower-layer cyclone. This joint evolution of the upper-layer meander trough and the lower-layer cyclone indicates that baroclinic instability is the dominant mechanism underlying the rapid amplification of the eastward propagating trigger meander.  相似文献   

17.
Surface temperature data obtained in and out of the bay all year round from March 1990 through February 1991, except from July through October 1990 were analyzed to investigate seasonal variability of theKyucho in Sukumo Bay, southwest of Shikoku, Japan. TheKyucho periodically occurs in the bay during both the warming period of March through June and the cooding period of November through February. The onset period of theKyucho is 8–15 days during the warming period and 4–14 days during the cooling period, giving an average of about 10 and 8 days, respectively. The position of the Kuroshio axis offshore in the south of Cape Ashizuri-misaki is a significant factor with theKyucho in the bay. Thermal infrared images taken by the NOAA-11 in the sea off east of Kyushu were also analyzed during the two observation periods. It is clearly found that a warm filament derived from the Kuroshio (KWF) advects northeast to Cape Ashizurimisaki along the Kuroshio, then encounters the southwest coast of Shikoku, followed by inducing theKyucho in the bay by the warm water intrusion. The alongshelf dimension of the KWFs is approximately 50–100 km, and the cross-shelf distance from the western edge of the KWFs to that of the body of the east Kuroshio is about 30–50 km. The KWF sometimes closely approaches to the east coast of Kyushu. An onshore meander of the Kuroshio front around Cape Toimisaki might grow into a KWF in the sea off east of Kyushu.  相似文献   

18.
Empirical orthogonal function(EOF) analysis was applied to a 50-year long time series of monthly mean positions of the Kuroshio path south of Japan from a regional reanalysis. Three leading EOF modes characterize the contributions from three typical paths of the Kuroshio meander: the typical large meander path, the offshore nonlarge meander path, and the nearshore non-large meander path, respectively. Accordingly, the spatial variation characteristics of oceanic anomaly fields can be depicted by...  相似文献   

19.
During the concentrated observation (April–May 1988) conducted as a part of the Ocean Mixed Layer Experiment (OMLET) in the sea area south of Japan, a conspicuous outbreak of warm water occurred from the large-meander region of the Kuroshio toward the southwest in the direction of the former Ocean Weather Station “T”. A series of NOAA-AVHRR infrared images clearly showed the process of this event. A surface buoy-mooring system deployed in this experiment recorded the arrival of this outbreak of water, in terms of the rise of sea-surface temperature (SST) of 1.5°C and the flow of warm water of 1.5kt toward the northwest at “T”. We studied this phenomenon by combining time series of infrared SST images with the oceanographic data obtained by two research vessels. The warm water was about 100 m deep in the section at 137°E along the edge of the Off-Shikoku Warm Water. It was estimated that about twenty outbreaks of this kind in a year can compensate a large heat loss to the atmosphere above this ocean region.  相似文献   

20.
张培军  王强 《海洋科学》2015,39(5):106-113
基于1.5层浅水方程模式,利用条件非线性最优参数扰动(CNOP-P)方法,研究模式参数的不确定性对黑潮大弯曲路径预报的影响。研究表明,单个模式参数误差如侧向摩擦系数误差、界面摩擦系数误差以及在不同季节具有不同约束的风应力大小误差,对黑潮大弯曲路径预报的影响较小,并且对背景流场的选取具有一定的敏感性;所有模式参数误差同时存在时对黑潮大弯曲路径预报具有一定的影响,并且预报结果在9个月左右不能被接受。因此,要提高黑潮大弯曲路径的预报技巧,模式中的参数需要给出更好的估计。  相似文献   

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