Monitoring of generation and propagation of the Kuroshio small meander using sea level data along the southern coast of Japan

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.     

Water and flow variations in Sagami Bay under the influence of the Kuroshio path

Variations of water and flow in Sagami Bay in relation to the Kuroshio path variations are examined by using 100m-depth temperature and salinity data from 25 stations as well as sea level data from five stations (Minami-Izu, ItÔ, Ôshima, Aburatsubo, Mera). In regard to temperature, anomalies from the mean seasonal variations are used. Results show that water properties are clearly different between the three typical paths of the Kuroshio. The difference is more remarkable in temperature than in salinity; temperature is higher during the typical large-eander (LM) path, and lower during the offshore non-large-meander (NLM) path, compared with the nearshore NLM path. Temperature anomaly and salinity distributions, as well as the Ôshima minus Minami-Izu and Ôshima minus Mera sea-level differences strongly suggest that the flows during the typical LM path are distributed as hitherto described in past studies, that is, water in the mouth region of the bay flows clockwise around Ôshima from the west channel to the east channel, and a counterclockwise eddy exists in the interior. On the other hand, flows during the nearshore and offshore NLM paths seem to be quite different from those during the typical LM path; velocities are very weak, and the directions of circulation is frequently reversed. This tendency also can be seen during parts of LM period in which the Kuroshio takes a non-typical LM path.Water properties in Sagami Bay are most characteristic during transitions between nearshore and offshore NLM paths. During transitions from nearshore to offshore NLM paths, temperatures are extremely high as a whole in the bay, while during reverse transitions, both temperatures and salinities are very low in the entire region.     

Spectral properties of sea level and time scales of Kuroshio path variations

Spectral properties of sea levels at Naze, Nishinoomote, Kushimoto, Uragami, Miyake-jima and HachijÔ-jima are examined for the non-large-meander (February 1964 – May 1975) and large-meander (October 1975 – December 1979) periods, and the periodicity of variation of the Kuroshio path is clarified.The large meander of the Kuroshio occurs with a primary period of about 20 years and secondary period of 7 to 8. 5 years. During the non-large-meander period, the Kuroshio alternately takes the nearshore and offshore non-large-meander paths with a primary period of 1. 6–1. 8 years. This variation is moreover composed of 110-day, around 195-day and annual periods. The 110-day variation of the Kuroshio path appears to have influence on the coastal sea levels between the Kii Peninsula and the Izu Ridge;i. e., the coastal sea levels rise and fall with one-month time lag after the Kuroshio has begun to approach and leave the Japanese coast. During the large-meander period, the 70 and 110-day variations are remarkable in sea levels south of Japan except Miyake-jima and HachijÔ-jima. The 70-day variation is highly coherent throughout the south coast of Japan; the coherent area of the 110-day variation seems to be smaller.The sea-level variations at Naze and Nishinoomote are not significantly coherent for any of the periods except for annual and semiannual cycles during both the non-large-meander and large-meander periods. That is, the sea-level variations are incoherent between the onshore and offshore sides of the Kuroshio, except for seasonal variation.     

Why does the Sea Level Difference between Kushimoto and Uragami Show Periods of Large Meander and Non-Large Meander Paths of the Kuroshio South of Japan?

The sea level difference between Kushimoto and Uragami, located to the west and east of the southern tip of the Kii Peninsula, is relatively large in periods of non-large meander path (nLMP) of the Kuroshio south of Japan in comparison with periods of large meander path (LMP). Based on this clear relationship, the sea level difference between Kushimoto and Uragami has been used as an index showing the periods of nLMP and those of LMP of the Kuroshio south of Japan. It has been pointed out that warm and saline Kuroshio water, separated from the main path of the Kuroshio, has a tendency to approach the western area off Kii Peninsula to off Muroto Peninsula in periods of nLMP, while it approaches the eastern area off Kii Peninsula to Omae-zaki in periods of LMP. On the basis of this observational evidences, the dynamic background underlaying the well-known relationship between the Kuroshio path and the sea level difference between Kushimoto and Uragami is examined in the present study, using the temperature and salinity data observed by Wakayama Prefectural Fisheries Experimental Station and Fisheries Research Institute of Mie. It is shown that deviations in vertically integrated specific volume off Kushimoto and Uragami almost equal deviations in observed sea level at Kushimoto and Uragami, respectively. It is also shown that the difference in vertically integrated specific volume between off Kushimoto and off Uragami almost equals the difference in observed sea level between Kushimoto and Uragami. As for the Kuroshio water, the high-temperature contribution is predominant for its specific volume rather than that of high salinity, which yields thermal expansion in comparison with coastal water. Because the difference in vertically integrated specific volume between off Kushimoto and off Uragami almost equals the difference in observed sea level between Kushimoto and Uragami, it is concluded that the relationship between the Kuroshio path and sea level difference between Kushimoto and Uragami is caused by the different approaching of the warm Kuroshio water between in nLMP periods and in LMP periods.     

A steady model of typical non-large-meander paths of the Kuroshio Current

Conditions south of Cape Shiono-misaki for the nearshore and offshore non-large-meander (NLM) paths of the Kuroshio Current are studied using a two-layer reduced gravity model. A steady and non-diffusive state is assumed, and the conservation laws of Bernoulli's function and potential vorticity along the current axis are used. Spatial changes of velocity and depth of the current are imposed as boundary conditions south of Cape Shiono-misaki. These conditions are based on the facts that are ohserved south of the cape: abrupt acceleration of the Kuroshio and the spatial change of sea levels. The current paths east of the cape are computed.This model reproduces well the actual nearshore NLM paths. It also produces offshore NLM paths west of and over the Izu Ridge, but not east of the Izu Ridge. Diffusion of vorticity may be important for the eastern part of the offshore NLM path.An increase of velocity south of the cape is necessary for producing realistic NLM paths. The velocity increase accompanies a decrease of current depth owing to Bernoulli's conservation, and the depth decrease in turn diminishes the absolute vorticity owing to the potential vorticity conservation. The velocity increase, on the other hand, strengthens the negative velocity shear and diminishes the relative vorticity. If the decreases of the relative and absolute vorticities compensate each other, the path goes excessively southward owing to the negative curvature south of the cape. Dominance of the relative vorticity change over the absolute vorticity change prevents, the path from shifting southward and causes the realistic NLM paths.The NLM paths need different amplitudes of the changes south of the cape depending on the velocity and transport of the current, but in any case, the nearshore NLM path needs larger changes than the offshore NLM path. This property and the amplitude of the changes are consistent with observations.     

Transition processes between the three typical paths of the Kuroshio

Transitions between the three typical paths of the Kuroshio south of Japan (the nearshore and offshore non-large-meander paths and the large-meander path) are described using sea level data at Miyake-jima and HachijÔ-jima in the Izu Islands and temperature data at a depth of 200 m observed from 1964 to 1975 and in 1980.In transitions between the nearshore and offshore non-large-meander paths the variation of the Kuroshio path occurs first in the region off Enshû-nada between the Kii Peninsula and the Izu Ridge and subsequently over the ridge. In the nearshore to offshore transition the offshore displacement of the path occurs first off Enshû-nada and then develops southeastwardly in the direction of HachijÔ-jima. In the reverse transition shoreward displacement occurs first off Enshû-nada and then throughout the region west and east of the Izu Ridge. The position of the Kuroshio south of Cape Shiono-misaki (the southernmost tip of the Kii Peninsula) is almost fixed near the coast throughout these transition periods, and significant variations of the Kuroshio path only occur east of the cape. The nearshore to offshore and offshore to nearshore transitions can be estimated to take about 25 and 35 days, respectively, during which the variation of the Kuroshio path over the Izu Ridge occurs for the last 11 and 25 days.The transitions between the non-large-meander and large-meander paths show that the large-meander path is mostly formed from the nearshore non-large-meander path and always changes to the offshore non-large-meander path.     

Sea level variations at the Izu Islands and typical stable paths of the Kuroshio

Differences in daily mean sea level between Kushimoto and Uragami and daily mean sea levels at Miyake-jima and HachijÔ-jima in the Izu Islands are examined during the 1964–1980 period, and characteristics of the typical paths of the Kuroshio corresponding to the dominant sea level states are described.Sea levels at the islands show three dominant states: high and low sea level states (45 % and 31 %) in the non-large-meander period (October 1963 –7 August 1975) and high sea level state (64 %) in the large-meander period (8 August 1975–15 March 1980). This indicates the existence of three typical paths of the Kuroshio, and the states correspond to the nearshore and offshore non-large-meander paths and the typical large-meander path, respectively. The first path is located near the coast throughout the whole southern area off Japan, the second path leaves the coast around the Izu Ridge and passes south of HachijÔ-jima, and the third path is located near the coast over the ridge after meandering far to the south of Enshû-nada.The positions of the three typical paths are almost the same in the farthest upstream and downstream regions south of Japan between 131E and 142E. The nearshore and offshore non-large-meander paths overlap between Kyûshû and the Kii Peninsula, being invariably close to the coast, while the typical large-meander path south of Shikoku is located offshore and changes its position meridionally.At the mid-depth of 400 m the nearshore non-large-meander and typical large-meander paths pass the Izu Ridge through the deep channel between Miyake-jima and HachijÔ-jima, while the offshore non-large-meander path passes through the deep region south of HachijÔjima. The path of the Kuroshio at mid-depth is well constrained by the bottom topography of the Izu Ridge.     

Sea level variations along the south coast of Japan and the large meander in the Kuroshio

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.     

日本南部黑潮与黑潮延伸体路径状态关联性的定量分析

日本南部黑潮存在多种路径模态:近岸非大弯曲路径、离岸非大弯曲路径和大弯曲路径。黑潮延伸体的路径存在两种典型模态:收缩态和伸展态。从地理位置看, 日本南部黑潮和黑潮延伸体是相邻的, 但它们的路径状态是否存在关联一直存在争议。本文基于卫星观测的海表高度资料和长期的海洋高分辨率再分析资料, 对日本南部黑潮和黑潮延伸体路径状态之间的关联性进行定量分析, 结果表明:日本南部黑潮和黑潮延伸体的路径状态存在一定的关联。当日本南部黑潮处于近岸非大弯曲和大弯曲路径时, 黑潮延伸体主要处于伸展态; 当日本南部黑潮处于离岸非大弯曲时, 黑潮延伸体处于伸展态和收缩态的比例相当。进一步分析表明, 黑潮流轴处于伊豆海脊的位置部分决定了上述关系, 可能存在其他因素调制了两者的关联性。     

Interannual correlations between sea level difference at the south coast of Japan and wind stress over the north pacific

Relationships of the sea level differences between Naze and Nishinoomote and between Kushimoto and Uragami with wind stress over the North Pacific are examined for interannual variability. These sea level differences are considered to be indications of Kuroshio transport in Tokara Strait and Kuroshio path south of Enshu-nada, respectively. In the sea level difference between Kushimoto and Uragami, dominant variations are found to have periods of about seven years and 3–4 years. The variation of about 7-year period, which corresponds to that in the Kuroshio path between the large meander and non-large meander, is coherent with the variation of the wind stress curl in a region about 2,400 km east of the Kii Peninsula, where negative stress curl weakens about two years before the sea level difference drops (i.e. the large meander path in the Kuroshio generates). The variation of the 3–4 year period is coherent with that of the wind stress in a large area covering the eastern equatorial Pacific, which suggests that it links with global-scale atmospheric variations. Interannual variation in sea level difference between Naze and Nishinoomote is not coherent with that between Kushimoto and Uragami, which suggests that it is not related to the variation of the Kuroshio path south of Enshu-nada, but is coherent with that of the zonally-integrated Sverdrup transport in the latitudinal zone along 30°N. It is suggested that the interannual variation of the Kuroshio transport in Tokara Strait can be explained by the barotropic response to the wind stress.     

Study on the Kuroshio and the Tsushima Current

I summarize the variations of the path of the Kuroshio and of the Tsushima Current mainly based on the results of my studies. The Tsushima Current forms three branches just after it enters the Japan Sea through the Tsushima Strait. The first and third branch currents flow along the Japanese and Korean coasts, respectively, and the second branch current flows from the western channel of the Tsushima Strait to the west of the Oki Islands only in summer from June to August. Properties of the topographic waves which are thought to work on the formation of the second branch are described mainly in terms of the dispersion relations. The Kuroshio has three typical paths,i.e., the nearshore and offshore non-large-meander paths and the typical large-meander path. The Kuroshio alternately takes the nearshore and offshore paths in the non-large-meander period, occasionally changes from the nearshore nonlarge-meander path to the large-meander path and, after having taken the large-meander path for several years, changes to the offshore non-large-meander path. Sea levels south of Japan are clearly different between the non-large-meander and large-meander periods, while they are not different between the periods of the nearshore and offshore non-large-meander paths. But, sea level and water properties in the coastal region show remarkable features during short periods of transitions between the typical non-large-meander paths. Future problems and subjects of studies on these currents are indicated. Especially, importance of velocity monitoring of the Kuroshio is emphasized, and a design of the observation across the Tokara Strait is proposed.     

Current Nature of the Kuroshio in the Vicinity of the Kii Peninsula

The Kuroshio flows very close to Cape Shionomisaki when it takes a straight path. The detailed observations of the Kuroshio were made both on board the R/V Seisui-maru of Mie University and on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station on June 11–14, 1996. It was confirmed that the current zone of the Kuroshio touches the coast and bottom slope just off Cape Shionomiaki, and that the coastal water to the east of the cape was completely separated from that to the west. The relatively high sea level difference between Kushimoto and Uragami could be caused by this separation of the coastal waters when the Kuroshio takes a straight path. This flow is rather curious, as the geostrophic flow, which has a barotropic nature and touches the bottom, would be constrained to follow bottom contours due to the vorticity conservation law. The reason why the Kuroshio leaves the bottom slope to the east of Cape Shionomisaki is attributed to the high curvature of the bottom contours there: if the current were to follow the contours, the centrifugal term in the equation of motion would become large and comparablee to the Coriolis (or pressure gradient) term, and the geostrophic balance would be destroyed. This creates a current-shadow zone just to the east of the cape. As the reason why the current zone of the Kuroshio intrudes into the coastal region to the west of the cape, it is suggested that the Kii Bifurcation Current off the southwest coast of the Kii Peninsula, which is usually found when the Kuroshio takes the straight path, has the effect of drawing the Kuroshio water into the coastal region. The sea level difference between Kushimoto and Uragami is often used to monitor the flow pattern of the Kuroshio near the Kii Peninsula. It should be noted that Uragami is located in the current shadow zone, while Kushimoto lies in the region where the offshore Kuroshio water intrudes into the coastal region. The resulting large sea level difference indicates that the Kuroshio is flowing along the straight path.     

Temporal-spatial oceanic variation in relation with the three typical Kuroshio paths south of Japan

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...     

POM模式在日本南部黑潮路径变异研究中的应用

日本南部黑潮路径变异对北太平洋地区的气候和环境具有显著的影响,对黑潮路径变异的研究具有重要的意义。本文利用POM(Princeton Ocean Model)数值模式模拟了日本南部黑潮的路径变异情况,分析了黑潮大弯曲路径形成的可能机制。研究结果表明,当黑潮处于非大弯曲路径时,相对位势涡度的平均值呈现递减趋势,说明日本南部低位势涡度水在不断积累,这样会使得四国再循环流的强度增强,迫使黑潮保持平直路径,同时,近岸黑潮垂直流速剪切增大,斜压不稳定性的作用也逐渐增大;当黑潮从非大弯曲路径向大弯曲路径过渡时,再循环流强度的减弱会导致黑潮的流速剪切减小。根据海表高度异常场以及海洋上层流场信息发现,近岸黑潮附近的气旋涡会随着再循环流区域反气旋涡的东侧向南运动,最终导致黑潮大弯曲的发生。分析涡流的能量,结果显示,黑潮大弯曲路径的形成与斜压不稳定性密切相关。     

Dynamic Structure of the Kuroshio South of Kyushu in Relation to the Kuroshio Path Variations

The variation of velocity and potential vorticity (PV) of the Kuroshio at the PN line in the East China Sea and the TK line across the Tokara Strait were examined in relation to the path variations of the Kuroshio in the southern region of Japan, using quarterly data from a conductivity-temperature-depth profiler and a shipboard acoustic Doppler current profiler during 1987–97. At the PN line the Kuroshio has a single stable current core located over the continental slope and a significant maximum of PV located just onshore of the current axis in the middle part of the main pycnocline. On the other hand, the Kuroshio at the TK line has double current cores over the two gaps in the Tokara Strait; the northern core has a much larger velocity than the southern core on average during periods of the large meander of the Kuroshio, while the difference in strength between the double cores is small during the non-large-meander (NLM) period. At the TK line, PV in the middle pycnocline is variable; it is small and nearly uniform throughout the section for 40% of the total observations, while it has a significant maximum near the northern core for 30% and two maxima corresponding to the double current cores for 23%. The small, nearly uniform PV occurs predominantly during the NLM period, and is closely related to the generation of the small meander of the Kuroshio southeast of Kyushu. This revised version was published online in July 2006 with corrections to the Cover Date.     

Monitoring of position of the Kuroshio axis in the Tokara Strait using sea level data

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.     

Variations of the Kuroshio Axis South of Kyushu in Relation to the Large Meander of the Kuroshio

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.     

Variability of Kuroshio velocity assessed from the sea-level difference between Naze and Nishinoomote

Variations of current velocity of the Kuroshio are examined using the 1965–1983 sea-level difference between Naze and Nishinoomote, located on the offshore and onshore sides of the Kuroshio in the Tokara Strait south of Kyûshû.Interannual variations of Kuroshio velocity are large, especially at periods longer than five years and around 2.1 years. They are almost determined by those of sea level on the offshore side of the Kuroshio. They are highly coherent with the offshore sea level at periods longer than 1.7 years, and incoherent with the onshore sea level at periods longer than 2.8 years.The mean seasonal variation averaged for 19 years is at its maximum in July and at its minimum in the second half of October, with a sharp decrease in August and September. However, such a variation does not repeat every year. Amplitude, dominant period and phase are greatly different by year, and they can be roughly divided into four groups: small-amplitude group, semiannual-period group, and two annual-period groups with different phases. The only feature found in almost all years is a weak velocity from September to December.The amplitude of seasonal variation tends to be large in the formation years of the large meander (LM) of the Kuroshio and small during the LM period. It is also large in the years preceding El Niño, and diminishes remarkably in El Niño years.Kuroshio velocity in the Tokara Strait is incoherent with position of the Kuroshio axis over the Izu Ridge, but highly coherent with 70-day variations of coastal sea levels which are dominant during the LM period.     

模式参数的不确定性对日本南部黑潮大弯曲路径预报的影响

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。     

Relationship between the path of the Kuroshio in the south of Japan and the path of the Kuroshio Extension in the east

A relationship between paths of the Kuroshio and Kuroshio Extension (KE) is investigated, using the satellite-derived altimetry dataset of 1993–2008. When the Kuroshio takes the nearshore nonlarge meander path or typical large meander path and resultantly goes through the deeper channel (about 2500 m) of the Izu-Ogasawara Ridge, the KE path adopts a relatively stable state with the two quasi-stationary meanders. On the other hand, when the Kuroshio takes the offshore nonlarge meander path and then passes over the shallower part of the Ridge (about 1000 m), the KE path tends to be convoluted, i.e., an unstable state.