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1.
Akihiko Morimoto Shoichiro Kojima Sen Jan Daisuke Takahashi 《Estuarine, Coastal and Shelf Science》2009
We investigated the movement of the Kuroshio axis on the northeast shelf of Taiwan associated with the passage of typhoons, using sea surface current data observed by the ocean radar system on Yonaguni and Ishigaki islands. First, we examined daily Kuroshio axis variation on the northeast shelf of Taiwan during typhoon events. The ocean radar data showed that the Kuroshio axis moved onto the shelf after passages of typhoons. The Kuroshio moved onto the shelf and stayed there after the passage of Typhoon Hai-Tang; while the Kuroshio maintained this pattern, southerly wind blew continuously for 4 days. The mean current speed northeast of Taiwan after the typhoon's passage increased by 18 cm s−1. In addition, the sea level difference between two satellite altimetry tracks east of Taiwan increased by 14.4 cm. These results suggest that coastal upwelling east of Taiwan caused by the southerly wind generated an east–west sea level difference that, in turn, generated a northward geostrophic current. This current could have enhanced the Kuroshio east of Taiwan, and pushed it onto the shelf. 相似文献
2.
Masaki Kawabe 《Journal of Oceanography》1980,36(4):227-235
The sea level difference between Naze and Nishinoomote and sea level anomalies (the residuals after removal of seasonal variations) around the Nansei Islands were examined in relation to the large meander in the Kuroshio south of central Japan. They are indices of surface velocity and geostrophic transport of the Kuroshio in the Tokara Strait and in the East China Sea, respectively. All of them were large during the meandering period, and each of them reached a maximum before or after the generation of the large meander in 1975. Thus the surface velocity and the geostrophic transport of the Kuroshio in the Tokara Strait and the East China Sea were large during the meandering period. The sea level difference between Naze and Nishinoomote (or Makurazaki) shows that the surface velocity and geostrophic transport in the Tokara Strait were significantly larger during the extinction stage in 1963 and during the generation stage in 1975 and were correlated with the position of the Kuroshio east of Kyûshû in 1974 and 1975 before the generation of the large meander.The surface velocity of the Kuroshio southeast of Yakushima (E-line) based on dynamic calculation referred to 1,000 db was weak during the meandering period, and was out of phase with the variation of surface velocity in the Tokara Strait monitored by tide gauge data. The analysis of GEK and hydrographic data shows that southwestward flow existed below 600 m in the slope region on the E-line and weakened during the meandering period. Thus, the out-of-phase variation in surface velocity mentioned above seems to be partly explained by the variation in velocity on the reference level at the E-line. 相似文献
3.
由于卫星高度计数据分辨率高、观测范围广的特点,我们使用该数据开展了黑潮流的研究。在之前的研究中,卫星绝对地转流都被用于对黑潮流域的表层流场的时空变化特征进行研究,并采用了一些探测方法提取了黑潮流轴和流路。然而,海面绝对地转流是由绝对动力地形估计得到,应该被当做实际流场的地转分量,在实际应用中并不能代表真实流场。在本研究中,建立了气候态绝对地转流与网格平均的漂流浮标流场间的数学校验关系,以此对卫星绝对地转流场进行修正,即便这两种数据的性质存在些许偏差。因此,基于主成分探测法,修正后的卫星绝对地转流被用于探测黑潮流轴和流路。对比结果表明,由修正后的卫星地转流场探测得到的黑潮流轴和流路均要好于地转流和表层流估计结果。修正后的地转流有助于开展更加准确的黑潮流轴和流路的逐日探测。 相似文献
4.
Motohiko Kashima Shiro Imawaki Shin-Ichiro Umatani Hiroshi Uchida Yuji Hashibe Hiroshi Ichikawa Masao Fukasawa 《Journal of Oceanography》2003,59(3):291-301
Theoretically, the geostrophic approximation holds for the low-frequency flow field, but no detailed examination has been
done on how well the estimated geostrophic velocity corresponds with the observed velocity. Intensive surveys were carried
out during 1993–1995 in the Kuroshio and its recirculation regions south of Shikoku, Japan, including repeated hydrographic
surveys and direct current measurements at nominal depths of 700, 1500 and 3000 m. For these depth intervals, vertical differences
of estimated geostrophic velocity are compared with those of observed velocity. For the intermediate layer (between 700 and
1500 m depths), the slope of the regression line is 0.99, correlation coefficient is 0.98, and the root-mean-square of difference
from geostrophic balance is 2.8 cm/s which is close to the estimated error of 2.1 cm/s. For the deep layer (between 1500 and
3000 m depths), the corresponding values are 0.82, 0.93, 1.2 cm/s and 2.0 cm/s, respectively. The results indicate that the
estimated geostrophic velocity compares well with the observed velocity in these regions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
稳态海面地形(MDT)是大地测量学家和海洋学家共同关心的一个重要物理量。该文基于WHU2009全球平均海面高模型和GO_CONS_GCF_2_TIM_R3纯GOCE重力场模型,采用几何法经高斯滤波处理后确定了全球稳态海面地形,与CLS09及DTU10M DTs相比,其差值均方根RMS均小于8 cm,表明该文结果具有较高的精度;根据地转流方程计算了相应的表层地转流,与GRACE重力场模型GGM03S结果相比,GOCE重力场模型所确定的表层地转流在墨西哥湾流、黑潮及厄加勒斯海流等海域均体现了更强的流速和更多的细部特征,验证了GOCE在洋流探测中的优势。 相似文献
6.
Hirohiko Nakamura Ayako Nishina Kotaro Tabata Masataka Higashi Akimasa Habano Toru Yamashiro 《Journal of Oceanography》2012,68(2):321-336
A time series of surface geostrophic velocity is developed using satellite altimetry data during 1992–2010 for a track across
the Kuroshio southeast of Kyushu, Japan. The temporal mean geostrophic velocity is estimated by combining the along-track
sea level anomaly and shipboard ADCP data. This approximately 6-km resolution dataset is successful in representing the Kuroshio
cross-current structure and temporal variation of the Kuroshio current-axis position during 2000–2010. The authors use this
dataset to examine the winter Kuroshio path destabilization phenomenon. Its seasonal features are characterized as follows:
the velocity shear on the inshore side of the Kuroshio becomes stronger and the Kuroshio path state becomes unstable from
the summer to winter. This evidence is consistent with the hypothetical mechanism governing the destabilization phenomenon
discussed in a previous study. Furthermore, the interannual amplitude modulation of the seasonality is examined in relation
to interannual variations in the winter northerly wind over the northern Okinawa Trough and the Pacific Decadal Oscillation
(PDO) index. The destabilization phenomenon appears 15 times in the period 2000–2010. Ten cases are related to local wind
effects, and 7 of these are also connected with the PDO index. This is probably because the winter northerly wind over the
northern Okinawa Trough is regulated by the PDO signal in interannual time-scales. Only 4 cases are related to the PDO index,
but their driving mechanism remains uncertain. 相似文献
7.
8.
Variability of Kuroshio velocity assessed from the sea-level difference between Naze and Nishinoomote 总被引:1,自引:0,他引:1
Masaki Kawabe 《Journal of Oceanography》1988,44(6):293-304
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. 相似文献
9.
Yutaka Nagata Junichi Takeuchi Makoto Uchida Isamu Ishikura Yoshitaka Morikawa Takashi Koike 《Journal of Oceanography》1999,55(3):407-416
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. 相似文献
10.
Ryoko Tokeshi Kaoru Ichikawa Satoshi Fujii Kenji Sato Shoichiro Kojima 《Journal of Oceanography》2007,63(4):711-720
A method to extract geostrophic current in the daily mean HF radar data in the Kuroshio upstream region is established by
comparison with geostrophic velocity determined from the along-track altimetry data. The estimated Ekman current in the HF
velocity is 1.2% (1.5%) and 48° (38°)-clockwise rotated with respect to the daily mean wind in (outside) the Kuroshio. Furthermore,
additional temporal smoothing is found necessary to remove residual ageostrophic currents such as the inertial oscillation.
After removal of the ageostrophic components, the HF geostrophic velocity agrees well with that from the altimetry data with
rms difference 0.14 (0.12) m/s in (outside) the Kuroshio. 相似文献
11.
12.
Mesoscale Eddies Observed by TOLEX-ADCP and TOPEX/POSEIDON Altimeter in the Kuroshio Recirculation Region South of Japan 总被引:1,自引:0,他引:1
Mesoscale eddies in the Kuroshio recirculation region south of Japan have been investigated by using surface current data measured by an Acoustic Doppler Current Profiler (ADCP) installed on a regular ferry shuttling between Tokyo and Chichijima, Bonin Islands, and sea surface height anomaly derived from the TOPEX/POSEIDON altimeter. Many cyclonic and anticyclonic eddies were observed in the region. Spatial and temporal scales of the eddies were determined by lag-correlation analyses in space and time. The eddies are circular in shape with a diameter of 500 km and a temporal scale of 80 days. Typical maximum surface velocity and sea surface height anomaly associated with the eddies are 15–20 cm s–1 and 15 cm, respectively. The frequency of occurrence, temporal and spatial scales, and intensity are all nearly the same for the cyclonic and anticyclonic eddies, which are considered to be successive wave-like disturbances rather than solitary eddies. Phase speed of westward propagation of the eddies is estimated as 6.8 cm s–1, which is faster than a theoretical estimate based on the baroclinic first-mode Rossby wave with or without a mean current. The spatial distribution of sea surface height variations suggests that these eddies may be generated in the Kuroshio Extension region and propagate westward in the Kuroshio recirculation region, though further studies are needed to clarify the generation processes. 相似文献
13.
Effect of Taiwan Strait Current on the onshore intrusion of Kuroshio: A geostrophic adjustment model
Young Ho Seung 《Ocean Science Journal》2012,47(1):41-50
The effect of the Taiwan Strait Current on the onshore intrusion of Kuroshio, both contributing to the formation of Tsushima
Warm Current, is addressed theoretically by invoking a geostrophic adjustment model previously proposed. The idealized model
assumes two unbounded basins, shallow and deep, separated by an infinitely long and thin barrier. On either side of the barrier,
a western boundary current in the deep basin and a shelf current in the shallow basin flow along the barrier with the surface
elevation of the former higher than that of the latter. When a part of the barrier is removed and a gap is created, the onshore
part of the western boundary current intrudes onto the shallow basin through the gap while conserving its potential vorticity.
Both the intruding current and the shelf current will later geostrophically adjust themselves to the disturbances created
by the intrusion. Model results show that the transport of onshore intrusion increases with the sea level difference imposed
initially between the deep and shallow basins across the barrier, indicating that the sea level rise associated with the strengthening
of shelf current inhibits the shelf-ward intrusion. The intruding current is in jet mode when its transport is maximized,
which otherwise is in coastal mode. The maximization of transport occurs when the sea level difference between the two basins
is sufficiently large. Although this model greatly idealizes the problem, it explains well the observed fact that the transport
of Tsushima Warm Current is fed mostly by the Taiwan Strait Current in summer when the latter becomes the strongest, and by
the onshore intrusion of Kuroshio in winter when the Taiwan Strait Current nearly vanishes, suggesting that the seasonal variation
of the onshore intrusion of Kuroshio is largely due to the seasonal variation in the strength of the Taiwan Strait Current. 相似文献
14.
Detecting fluctuations of the Kuroshio axis south of Japan using TOPEX/POSEIDON altimeter data 总被引:1,自引:0,他引:1
Shiro Imawaki Mayumi Gotoh Hiroyuki Yoritaka Noriya Yoshioka Atsunobu Misumi 《Journal of Oceanography》1996,52(1):69-92
Sea surface dynamic topography (SSDT) can be divided into temporal mean SSDT and fluctuation SSDT. The former is approximated with a climatological mean SSDT and the latter is derived from satellite altimetry data, to give an approximated total SSDT (called a composite SSDT). The method is applied to detecting fluctuations of the Kuroshio axis south of Japan using TOPEX/POSEIDON altimeter data from the first year mission in 1992–1993. The fluctuation SSDT averaged over a wide area south of Japan clearly shows an annual cycle with an amplitude of about 15 cm. Temporal changes of SSDT along a subsatellite track crossing the Kuroshio compare moderately well with those estimated from repeated hydrographic observations, although there is a discrepancy of unknown origin. The composite SSDT also compares well with SSDT estimated from the same hydrographic data. Horizontal distribution of the surface geostrophic velocity component normal to subsatellite tracks is derived every ten days from the composite SSDT. Most locations of estimated strong eastward geostrophic velocities coincide well with locations of the Kuroshio axis determined every 15 days fromin situ surface velocity measurements on various vessels; for example, a fairly large meander of the Kuroshio south of Honshu is clearly detected. It is concluded that the composite SSDT can be used reliably to detect fluctuations of the Kuroshio axis south of Japan. 相似文献
15.
Hiroshi Ichikawa Hirohiko Nakamura Ayako Nishina Masataka Higashi 《Journal of Oceanography》2004,60(2):351-363
To better understand the mechanism underlying the variation of the Kuroshio south of central Japan, we have examined the variability
of current structure in its upstream region, southeast of Amami-Ohshima Island in the northern Ryukyu Islands. By combined
use of ship-mounted Acoustic Doppler Current Profiler (ADCP) and the TOPEX/POSEIDON satellite altimeter data on Path 214,
the sea surface absolute geostrophic currents were estimated every ten days from January 1998 to July 2002. The 4.5-year mean
surface current was found to flow northeastward north of 26.8°N with a maximum speed of 14 cm s−1 over the shelf slope at 3000 m depth. The moored current-meter observations at three or four mooring stations from Dec. 1998
to Oct. 2002 suggested the existence of a northeastward undercurrent with a maximum core velocity of 23 cm s−1 at 600 m depth over the shelf slope at 1600 m depth. The mean volume transport in the top 1500 m between 27.9°N and 26.7°N
is estimated to be 16 × 106 m3s−1 northeastward, including the subsurface core current related component of 4 × 106 m3s−1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
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
17.
Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data 总被引:2,自引:0,他引:2
Sea-surface geostrophic velocities for the Kuroshio region calculated from TOPEX/POSEIDON altimetry data together within situ oceanographic data are compared with surface velocities derived from drifting buoy trajectories. The geostrophic velocities
agree well with the observed velocities, suggesting that the Kuroshio surface layer is essentially in geostrophic balance,
within measurement error. The comparison is improved a little when the centrifugal acceleration is taken into account. The
observed velocities are divided into the temporal mean and fluctuation components, and the partitioning of velocities between
these two components is examined. For the Kuroshio region, most of the fluctuation components of the velocities derived from
drifting buoys are found to be positive. This result suggests that Eulerian mean velocities for the Kuroshio region estimated
from drifting buoy data tend to be larger than actual means, due to the buoy’s tendency to sample preferentially in the high-velocity
Kuroshio. 相似文献
18.
Kazuyuki Otsuka 《Journal of Oceanography》1986,42(2):106-118
Flow patterns and positions of the Kuroshio in the vicinity of the Izu Ridge are clarified by analyzing hydrographic observations and daily mean sea levels at Hachijo-jima, Miyake-jima and Oshima in the period from 1964 to 1981.Correlations are calculated between differences of dynamic depth anomaly at the surface refered to 1,000 db and differences of daily mean sea level between the two islands. The datum line of the tidal station at Hachijo-jima is about 90 cm higher than that at Miyake-jima, and about 20 cm higher than that at Oshima. A clear correlation is found between the cross-section transport of the Kuroshio and the mean sea-level difference between Hachijo-jima and Miyake-jima. The sea-level difference of the flow pattern without meander off Enshu-nada (type N) tends to be larger than that of the flow patterns with meander (type A and type B). This seems to indicate that the volume transport of the Kuroshio in the meandering period is smaller than that during the straight path period. Large sudden increases or decreases in the mean sea-level difference occur when the flow pattern changes and the Kuroshio axis shifts. The frequency of occurrence of quiet periods in the sea-level difference reflect the flow pattern of the Kuroshio. 相似文献
19.
The aim of this study is to elucidate the seasonal variation in the volume transport through the Tsushima-Korea Strait using the sea level difference across the Strait. The sea level difference associated with the baroclinic motion is estimated from the geostrophic current profile, which is calculated as its vertical integrated transport is zero, using the CTD data from 1988 to 1990. The sea level difference associated with the barotropic motion is estimated by subtracting the sea level difference associated with the baroclinic motion from the observed one. The range (maximum-minimum) of the seasonal variation in the volume transport is evaluated about 0.7 Sv on the average, using the sea level difference associated with the barotropic motion. It is one third of the seasonal variation in the volume transport which is estimated from observed sea level difference on the assumption that no baroclinic component exists. Such analyses also indicate that the volume transport was at a maximum in early winter and at a minimum in early spring from 1988 to 1990. The negative correlation is also found between the volume transport through the eastern channel and that through the western channel. Moreover, it is noticed that the seasonal variation in the surface current velocity in the Strait largely contains baroclinic motions which are locally caused in the Tsushima-Korea Strait. 相似文献
20.
The correlation between the Kuroshio and coastal sea level south of Japan has been examined using the altimetry and tide gauge
data during the period 1992–2000. The sea level varies uniformly in a region bounded by the coast and the mean Kuroshio axis,
which stretches for several hundred kilometers along the coast. These variations are related with the Kuroshio velocity, as
coastal sea level decreases (or increases) when the Kuroshio is faster (or slower). To the east of the Kii Peninsula, where
sea level variations are different from these to the west, movement of the Kuroshio axis additionally affects coastal sea
level variations. 相似文献