The Experts below are selected from a list of 942 Experts worldwide ranked by ideXlab platform
Kunio Kutsuwada - One of the best experts on this subject based on the ideXlab platform.
-
impact of wind wind stress field in the north pacific constructed by adeos nscat data
Journal of Oceanography, 1998Co-Authors: Kunio KutsuwadaAbstract:Data sets of surface wind and wind-stress fields in the North Pacific from September 1996 to June 1997 have been constructed using NASA Scatterometer (NSCAT) data on-board ADEOS to investigate their variability and implications for the wind-driven oceanic circulation. Using a weighting function decreasing with the distance between each grid and data points, and of Gaussian type for time, daily, 10-day and monthly averages are calculated for each 1°×1° grid. Products are validated by comparison with those calculated from in-situ measurement data at oceanic buoys around Japan (JMA) and in the equatorial area (TAO). The RMS differences for wind direction and speed never exceed 20° and 2 ms−1, respectively, for the TAO buyos. This does not hold for data taken by JMA buoys, suggesting that the reliability in the mid-latitudes is not good for time averages shorter than several days. Zonal integration of the Sverdrup Transport in a zone of 28°–30°N calculated from the monthly-mean products ranges between 25 and 60×106 m3s−1 (Sv) around its mean of 38 Sv. These are not so different from the Kuroshio Transport values calculated from oceanic measurements.
-
interannual variability of the kuroshio Transport in response to the wind stress field over the north pacific its relation to the path variation south of japan
Journal of Geophysical Research, 1996Co-Authors: Kazunori Akitomo, Toshiyuki Awaji, Kunio KutsuwadaAbstract:We have investigated the interannual variability in the Kuroshio Transport, focusing on the baroclinic response of the upper ocean to the long-term variation of the wind stress field over the North Pacific from 1961 to 1987. First, temporal change of the Kuroshio Transport at the western boundary from 17° to 31°N has been estimated on the assumptions that the Kuroshio is a baroclinic flow confined in the upper layer and that the effect of interior wind stress curl on the volume Transport at the western boundary is transferred by nondispersive baroclinic Rossby wave. Peak values in the estimated Transport appear in its beginning region (17°–21°N) when or just before the Kuroshio settles into a meandering state south of Japan in 1975, 1981, and 1986. These peaks are due to negative wind stress curl anomalies which are induced by the intensified trade winds in the central and eastern tropical North Pacific on and just after an El Nino event and in the western tropical North Pacific months to years before the next El Nino event. Such peaks are not found in the barotropic Sverdrup Transport. In downstream regions, i.e., in the East China Sea and south of Japan (north of 23°N), on the contrary, the estimated Transports (through baroclinic and barotropic responses) do not have such good correlation to the path variation. Temporal change in thermocline depths estimated from bathythermograph data clearly shows the westward propagations of positive anomalies by nondispersive baroclinic Rossby waves at latitudes of the beginning of the Kuroshio (south of 21°N), which is in phase with peaks of the Kuroshio baroclinic Transport at the western boundary. On the other hand, there are only the local propagations of the anomalies in the downstream regions, as previous studies reported. However, it is emphasized that temporal change of the geostrophic Transport in the East China Sea (∼28°N) is coincident with that of the baroclinic Transport at the beginning of the Kuroshio, not with that at the same latitude. A numerical experiment with a nonlinear reduced-gravity model confirms that temporal changes of the Transport in the East China Sea and south of Japan are due to the advective (nonlinear) effect of the Kuroshio itself, while the linear baroclinic response to the wind stress field is dominant in its beginning region.
Amadou Thierno Gaye - One of the best experts on this subject based on the ideXlab platform.
-
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa
Ocean Science, 2018Co-Authors: Lala Kounta, Xavier Capet, Julien Jouanno, Nicolas Kolodziejczyk, Bamol Sow, Amadou Thierno GayeAbstract:The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between ∼ 8 and 20°N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup Transport) located above the potential density σt = 26.7 kg m−3 in the model (approx. above 250m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward Transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with Transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region.
Torsten Kanzow - One of the best experts on this subject based on the ideXlab platform.
-
On the seasonal cycles and variability of Florida Straits, Ekman and Sverdrup Transports at 26° N in the Atlantic Ocean
Ocean Science, 2010Co-Authors: C. P. Atkinson, Harry L. Bryden, Joël J.-m. Hirschi, Torsten KanzowAbstract:Abstract. Since April 2004 the RAPID array has made continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC) at 26° N. Two key components of this system are Ekman Transport zonally integrated across 26° N and western boundary current Transport in the Florida Straits. Whilst measurements of the AMOC as a whole are somewhat in their infancy, this study investigates what useful information can be extracted on the variability of the Ekman and Florida Straits Transports using the decadal timeseries already available. Analysis is also presented for Sverdrup Transports zonally integrated across 26° N. The seasonal cycles of Florida Straits, Ekman and Sverdrup Transports are quantified at 26° N using harmonic analysis of annual and semi-annual constituents. Whilst Sverdrup Transport shows clear semi-annual periodicity, calculations of seasonal Florida Straits and Ekman Transports show substantial interannual variability due to contamination by variability at non-seasonal frequencies; the mean seasonal cycle for these Transports only emerges from decadal length observations. The Florida Straits and Ekman mean seasonal cycles project on the AMOC with a combined peak-to-peak seasonal range of 3.5 Sv. The combined seasonal range for heat Transport is 0.40 PW. The Florida Straits seasonal cycle possesses a smooth annual periodicity in contrast with previous studies suggesting a more asymmetric structure. No clear evidence is found to support significant changes in the Florida Straits seasonal cycle at sub-decadal periods. Whilst evidence of wind driven Florida Straits Transport variability is seen at sub-seasonal and annual periods, a model run from the 1/4° eddy-permitting ocean model NEMO is used to identify an important contribution from internal oceanic variability at sub-annual and interannual periods. The Ekman Transport seasonal cycle possesses less symmetric structure, due in part to different seasonal Transport regimes east and west of 50 to 60° W. Around 60% of non-seasonal Ekman Transport variability occurs in phase section-wide at 26° N and is related to the NAO, whilst Sverdrup Transport variability is more difficult to decompose.
-
On the variability of Florida Straits and wind driven Transports at 26° N in the Atlantic Ocean
2010Co-Authors: C. P. Atkinson, Harry L. Bryden, Joël J.-m. Hirschi, Torsten KanzowAbstract:Since April 2004 the RAPID array has made continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC) at 26° N. Two key components of this system are Ekman Transport zonally integrated across 26° N and western boundary current Transport in the Florida Straits. Whilst measurements of the AMOC as a whole are somewhat in their infancy, this study investigates what useful information can be extracted on the variability of the Ekman and Florida Straits Transports using the decadal timeseries already available. Analysis is also presented for Sverdrup Transports zonally integrated across 26° N. The seasonal cycles of Florida Straits, Ekman and Sverdrup Transports are quantified at 26° N using harmonic analysis of annual and semi-annual constituents. Whilst Sverdrup Transport shows clear semi-annual periodicity, calculations of seasonal Florida Straits and Ekman Transports show substantial interannual variability due to variability at non-seasonal frequencies; the mean seasonal cycle for these Transports only emerges from decadal length observations. The Florida Straits and Ekman mean seasonal cycles project on the AMOC with a combined peak-to-peak seasonal range of 3.5 Sv. The combined seasonal range for heat Transport is 0.40 PW. The Florida Straits seasonal cycle possesses a smooth annual periodicity in contrast with previous studies suggesting a more asymmetric structure. No clear evidence is found to support significant changes in the Florida Straits seasonal cycle at sub-decadal periods. Whilst evidence of wind driven Florida Straits Transport variability is seen at sub-seasonal and annual periods, model runs from the 1/4° eddy-permitting ocean model NEMO are used to identify an important contribution from internal oceanic variability at sub-annual and interannual periods. The Ekman Transport seasonal cycle possesses less symmetric structure, due in part to different seasonal Transport regimes east and west of 50 to 60° W. Around 60% of non-seasonal Ekman Transport variability occurs in phase section-wide at 26° N and is related to the NAO, whilst Sverdrup Transport variability is more difficult to decompose.
-
On the seasonal cycles and variability of Florida Straits, Ekman and Sverdrup Transports at 26° N in the Atlantic Ocean
Copernicus Publications, 2010Co-Authors: C. P. Atkinson, Harry L. Bryden, Joël J.-m. Hirschi, Torsten KanzowAbstract:Since April 2004 the RAPID array has made continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC) at 26° N. Two key components of this system are Ekman Transport zonally integrated across 26° N and western boundary current Transport in the Florida Straits. Whilst measurements of the AMOC as a whole are somewhat in their infancy, this study investigates what useful information can be extracted on the variability of the Ekman and Florida Straits Transports using the decadal timeseries already available. Analysis is also presented for Sverdrup Transports zonally integrated across 26° N. <br><br> The seasonal cycles of Florida Straits, Ekman and Sverdrup Transports are quantified at 26° N using harmonic analysis of annual and semi-annual constituents. Whilst Sverdrup Transport shows clear semi-annual periodicity, calculations of seasonal Florida Straits and Ekman Transports show substantial interannual variability due to contamination by variability at non-seasonal frequencies; the mean seasonal cycle for these Transports only emerges from decadal length observations. The Florida Straits and Ekman mean seasonal cycles project on the AMOC with a combined peak-to-peak seasonal range of 3.5 Sv. The combined seasonal range for heat Transport is 0.40 PW. <br><br> The Florida Straits seasonal cycle possesses a smooth annual periodicity in contrast with previous studies suggesting a more asymmetric structure. No clear evidence is found to support significant changes in the Florida Straits seasonal cycle at sub-decadal periods. Whilst evidence of wind driven Florida Straits Transport variability is seen at sub-seasonal and annual periods, a model run from the 1/4° eddy-permitting ocean model NEMO is used to identify an important contribution from internal oceanic variability at sub-annual and interannual periods. The Ekman Transport seasonal cycle possesses less symmetric structure, due in part to different seasonal Transport regimes east and west of 50 to 60° W. Around 60% of non-seasonal Ekman Transport variability occurs in phase section-wide at 26° N and is related to the NAO, whilst Sverdrup Transport variability is more difficult to decompose
Lala Kounta - One of the best experts on this subject based on the ideXlab platform.
-
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa
Ocean Science, 2018Co-Authors: Lala Kounta, Xavier Capet, Julien Jouanno, Nicolas Kolodziejczyk, Bamol Sow, Amadou Thierno GayeAbstract:The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between ∼ 8 and 20°N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup Transport) located above the potential density σt = 26.7 kg m−3 in the model (approx. above 250m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward Transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with Transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region.
Magdalena Andres - One of the best experts on this subject based on the ideXlab platform.
-
Manifestation of the Pacific Decadal Oscillation in the Kuroshio
'American Geophysical Union (AGU)', 2019Co-Authors: Magdalena Andres, Kim KuhAbstract:Pacific Decadal Oscillation (PDO) index is strongly correlated with vertically integrated Transport carried by the Kuroshio through the East China Sea (ECS). Transport was determined from satellite altimetry calibrated with in situ data and its correlation with PDO index (0.76) is highest at zero lag. Total PDO-correlated Transport variation carried by the ECS-Kuroshio and Ryukyu Current is about 4 Sv. In addition, PDO index is strongly negatively correlated, at zero lag, with NCEP wind-stress-curl over the central North Pacific at ECS latitudes. Sverdrup Transport, calculated from wind-stress-curl anomalies, is consistent with the observed Transport variations. Finally, PDO index and ECS-Kuroshio Transport are each negatively correlated with Kuroshio Position Index in the Tokara Strait; this can be explained by a model in which Kuroshio path is steered by topography when Transport is low and is inertially controlled when Transport is high. Citation: Andres, M., J.-H. Park, M. Wimbush, X.-H. Zhu, H. Nakamura, K. Kim, and K.-I. Chang (2009), Manifestation of the Pacific Decadal Oscillation in the Kuroshio, Geophys. Res. Lett., 36, L16602, doi:10.1029/2009GL039216.X1129sciescopu
-
manifestation of the pacific decadal oscillation in the kuroshio
Geophysical Research Letters, 2009Co-Authors: Magdalena Andres, Jaehun Park, Mark Wimbush, Xiaohua Zhu, Hirohiko Nakamura, Kuh Kim, Kyungil ChangAbstract:[1] Pacific Decadal Oscillation (PDO) index is strongly correlated with vertically integrated Transport carried by the Kuroshio through the East China Sea (ECS). Transport was determined from satellite altimetry calibrated with in situ data and its correlation with PDO index (0.76) is highest at zero lag. Total PDO-correlated Transport variation carried by the ECS-Kuroshio and Ryukyu Current is about 4 Sv. In addition, PDO index is strongly negatively correlated, at zero lag, with NCEP wind-stress-curl over the central North Pacific at ECS latitudes. Sverdrup Transport, calculated from wind-stress-curl anomalies, is consistent with the observed Transport variations. Finally, PDO index and ECS-Kuroshio Transport are each negatively correlated with Kuroshio Position Index in the Tokara Strait; this can be explained by a model in which Kuroshio path is steered by topography when Transport is low and is inertially controlled when Transport is high.
-
study of the kuroshio ryukyu current system based on satellite altimeter and in situ measurements
Journal of Oceanography, 2008Co-Authors: Magdalena Andres, Jaehun Park, Mark Wimbush, Xiaohua Zhu, Kyungil Chang, Hiroshi IchikawaAbstract:Data from satellite altimeters and from a 13-month deployment of in situ instruments are used to determine an empirical relationship between sea-level anomaly difference (SLA) across the Kuroshio in the East China Sea (ECS-Kuroshio) and net Transport near 28°N. Applying this relationship to the altimeter data, we obtain a 12-year time series of ECS-Kuroshio Transport crossing the C-line (KT). The resulting mean Transport is 18.7 ± 0.2 Sv with 1.8 Sv standard deviation. This KT is compared with a similarly-determined time series of net Ryukyu Current Transport crossing the O-line near 26°N southeast of Okinawa (RT). Their mean sum (24 Sv) is less than the mean predicted Sverdrup Transport. These KT and RT mean-flow estimates form a consistent pattern with historical estimates of other mean flows in the East China Sea/Philippine Basin region. While mean KT is larger than mean RT by a factor of 3.5, the amplitude of the KT annual cycle is only half that of RT. At the 95% confidence level the Transports are coherent at periods of about 2 years and 100–200 days, with RT leading KT by about 60 days in each case. At the annual period, the Transports are coherent at the 90% confidence level with KT leading RT by 4–5 months. While the bulk of the Kuroshio enters the ECS through the channel between Taiwan and Yonaguni-jima, analysis of satellite altimetry maps, together with the Transport time series, indicates that the effect of mesoscale eddies is transmitted to the ECS via the Kerama Gap southwest of Okinawa. Once the effect of these eddies is felt by the ECS-Kuroshio at 28°N, it is advected rapidly to the Tokara Strait.
