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Pearn P. Niiler - One of the best experts on this subject based on the ideXlab platform.
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pathways of marine debris derived from trajectories of lagrangian Drifters
Marine Pollution Bulletin, 2012Co-Authors: Nikolai Maximenko, Jan Hafner, Pearn P. NiilerAbstract:Abstract Global set of trajectories of satellite-tracked Lagrangian Drifters is used to study the dynamics of marine debris. A probabilistic model is developed to eliminate the bias in spatial distribution of Drifter data due to heterogeneous deployments. Model experiments, simulating long-term evolution of initially homogeneous Drifter array, reveal five main sites of Drifter aggregation, located in the subtropics and maintained by converging Ekman currents. The paper characterizes the geography and structure of the collection regions and discusses factors that determine their dynamics. A new scale R c = (4 k / |D |) 1/2 is introduced to characterize tracer distribution under competing effects of horizontal divergence D and diffusion k . Existence and locations of all five accumulation zones have been recently confirmed by direct measurements of microplastic at the sea surface.
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permanent meanders in the california current system
Journal of Physical Oceanography, 2008Co-Authors: Luca Centurioni, J C Ohlmann, Pearn P. NiilerAbstract:Surface Velocity Program (SVP) Drifter data from 1987 through 2005; Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) sea level anomalies; and NCEP reanalysis winds are used to assemble a time-averaged map of the 15-m-deep geostrophic velocity field in the California Current System seaward of about 50 km from the coast. The wind data are used to compute the Ekman currents, which are then subtracted from the Drifter velocity measurements. The resulting proxy for geostrophic velocity anomalies computed from Drifters and from satellite sea level measurements are combined to form an unbiased mean geostrophic circulation map. The result shows a California Current System that flows southward with four permanent meanders that can extend seaward for more than 800 km. Bands of alternating eastward and westward zonal currents are connected to the meanders and extend several thousand kilometers into the Pacific Ocean. This observed time-mean circulation and its associated eddy energy are compared to those produced by various high-resolution OGCM solutions: Regional Ocean Modeling System (ROMS; 5 km), Parallel Ocean Program model (POP; 1/10°), Hybrid Coordinate Ocean Model (HYCOM; 1/12°), and Naval Research Laboratory (NRL) Layered Ocean Model (NLOM; 1/32°). Simulations in closest agreement with observations come from ROMS, which also produces four meanders, geostrophic time-mean currents, and geostrophic eddy energy consistent with the observed values. The time-mean ageostrophic velocity in ROMS is strongest within the cyclonic part of the meanders and is similar to the ageostrophic velocity produced by nonlinear interaction of Ekman currents with the nearsurface vorticity field.
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observations of inflow of philippine sea surface water into the south china sea through the luzon strait
Journal of Physical Oceanography, 2004Co-Authors: Luca Centurioni, Pearn P. Niiler, Dongkyu LeeAbstract:Abstract Velocity observations near the surface made with Argos satellite-tracked Drifters between 1989 and 2002 provide evidence of seasonal currents entering the South China Sea from the Philippine Sea through the Luzon Strait. The Drifters cross the strait and reach the interior of the South China Sea only between October and January, with ensemble mean speeds of 0.7 ± 0.4 m s−1 and daily mean westward speeds that can exceed 1.65 m s−1. The majority of the Drifters that continued to reside in the South China Sea made the entry within a westward current system located at ∼20°N that crossed the prevailing northward Kuroshio path. In other seasons, the Drifters looped across the strait within the Kuroshio and exited along the south coast of Taiwan. During one intrusion event, satellite altimeters indicated that, directly west of the strait, anticyclonic and cyclonic eddies resided, respectively, north and south of the entering Drifter track. The surface currents measured by the crossing Drifters were much...
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dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations
Geophysical Research Letters, 2003Co-Authors: Pearn P. Niiler, Nikolai Maximenko, James C McwilliamsAbstract:[1] The 1992–2002 time-mean absolute sea level distribution of the global ocean is computed for the first time from observations of near-surface velocity. For this computation, we use the near-surface horizontal momentum balance. The velocity observed by Drifters is used to compute the Coriolis force and the force due to acceleration of water parcels. The anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in Drifter data distribution. NCEP reanalysis winds are used to compute the force due to Ekman currents. The mean sea level gradient force, which closes the momentum balance, is integrated for mean sea level. We find that our computation agrees, within uncertainties, with the sea level computed from the geostrophic, hydrostatic momentum balance using historical mean density, except in the Antarctic Circumpolar Current. A consistent horizontally and vertically dynamically balanced, near-surface, global pressure field has now been derived from observations.
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near surface dynamical structure of the kuroshio extension
Journal of Geophysical Research, 2003Co-Authors: Pearn P. Niiler, Nikolai Maximenko, Gleb Panteleev, Toshio Yamagata, Donald B OlsonAbstract:[1] Lagrangian data from 657 SVP Drifters, CNES/Aviso (Archiving, Validation, and Interpretation of Satellite Oceanographic data) time variable satellite altimeter sea level anomaly and Levitus 98 hydrographic data are used to develop 0.25° spatial resolution maps of the mean and eddy circulations in the northwestern Pacific during the 1990s. Drifter velocities at 15 m depth and 200 m temperature data clearly indicate in the Kuroshio Extension (KE) jet two prominent meanders that culminate in a 300 km northward deflection east of the Shatsky Rise at 160°E. The interannual trends of Aviso mesoscale variance are absent along the path of the meandering KE jet. Three anticyclonic recirculations can be identified south or southeast of the Kuroshio, the southernmost around Daito Island being a new discovery. About 3% of the Drifters with drogues attached crossed the Kuroshio front. The Aviso currents are correlated at 0.8 with Drifter geostrophic velocity. The Aviso geostrophic currents are adjusted in amplitude to the contemporaneous Drifter observations and are further used to compute an unbiased mean geostrophic circulation and the quasi-geostrophic Reynolds' stresses in the KE region. The principal axes of the eddy Reynolds' stresses are oriented along the unbiased mean velocity vectors within the meandering KE jet. The time-mean horizontal momentum balance that includes both the mean and eddy momentum convergences is used to compute absolute sea level map and its uncertainty. At 145°E the 2000 m depth absolute dynamic height referenced to the sea level reveals a heretofore unknown 70 dynamic cm drop from 25° to 42°N.
Michael H Graham - One of the best experts on this subject based on the ideXlab platform.
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reproductive longevity of drifting kelp macrocystis pyrifera phaeophyceae in monterey bay usa 1
Journal of Phycology, 2006Co-Authors: Gustavo Hernandezcarmona, Brent B Hughes, Michael H GrahamAbstract:Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long-distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera Drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach-cast Drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow Drifter trajectories and to measure drifting speed. Experimental Drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio-tagged Drifters was 7.12km.day � 1 , suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890km ( � 363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter-hemispheric gene flow.
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reproductive longevity of drifting kelp macrocystis pyrifera phaeophyceae in monterey bay usa 1
Journal of Phycology, 2006Co-Authors: Gustavo Hernandezcarmona, Brent B Hughes, Michael H GrahamAbstract:Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long-distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera Drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach-cast Drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow Drifter trajectories and to measure drifting speed. Experimental Drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio-tagged Drifters was 7.12km.day � 1 , suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890km ( � 363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter-hemispheric gene flow.
Luca Centurioni - One of the best experts on this subject based on the ideXlab platform.
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Submesoscale Vorticity and Divergence in the Alboran Sea: Scale and Depth Dependence
'Frontiers Media SA', 2021Co-Authors: Giovanni Esposito, Luca Centurioni, Maristella Berta, Pierre-marie Poulain, Tamay Özgökmen, T.m. Shaun Johnston, John Lodise, Annalisa GriffaAbstract:The statistics of submesoscale divergence and vorticity (kinematic properties, KPs) in the Alboran Sea (Mediterranean Sea) are investigated, using data from Drifters released during two experiments in June 2018 and April 2019 in the framework of the Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO) project. Surface Drifters sampling the first meter of water (CARTHE and CODE) and 15 m Drifters (SVP) are considered. The area of interest is dominated by processes of strong frontogenesis and eddy formation as well as mixing, related to the high lateral gradients between Mediterranean and Atlantic waters. Drifter coverage and distribution allow to investigate the dependence of KPs on horizontal scales in a range between 1 and 16 km, that effectively bridges submesoscale and mesoscale processes, and at two depths, of 1 and 15 m. For both experiments, the surface flow is highly ageostrophic at 1 km scale, with positive vorticity skewness indicating the presence of submesoscale features. Surface divergence quickly decreases at increasing scales with a slope compatible with a turbulent process with broadband wavenumber spectrum, suggesting the influence of surface boundary layer processes such as wind effects, waves and Langmuir cells at the smaller scales. Vorticity, on the other hand, has a significantly slower decay, suggesting interaction between submesoscale and mesoscale dynamics. Results at 15 m are characterized by reduced ageostrophic dynamics with respect to the surface, especially for divergence. Submesoscale processes are present but appear attenuated in terms of KP magnitude and skewness. The results are generally consistent for the two experiments, despite the observed differences in the mixed layer stratification, suggesting that submesoscale instabilities occur mostly at surface fronts associated with filaments of Atlantic and Mediterranean waters that are present in both cases. The results are compared with previous literature results in other parts of the world ocean and a synthesis is provided. Good agreement with previous surface results is found, suggesting some general properties for divergence and vorticity scale dependence. The importance of further investigating very high resolution frontal processes at scales of tens of meters, as well as processes of interaction with high wind effects is highlighted
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On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea
'MDPI AG', 2021Co-Authors: Pierre-marie Poulain, Luca Centurioni, Tamay Özgökmen, Daniel Tarry, Ananda Pascual, Simon Ruiz, Elena Mauri, Milena Menna, Giulio NotarstefanoAbstract:An Algerian Eddy, anticyclonic vortex generated by the instability of the Algerian Current in the southwestern Mediterranean Sea, is studied using data provided by Drifters (surface currents), Argo floats (temperature and salinity profiles), environmental satellites (absolute dynamic topography maps and ocean color images) and operational oceanography products. The eddy was generated in May 2018 and lasted as an isolated vortex until November 2018. Its morphology and kinematics are described in June–July 2018 when Drifters were trapped in its core. During that period, the eddy was slowly moving to the NE (~2 km/day), with an overall diameter of about 200 km (slowly growing with time) and maximal surface swirl velocity of ~50 cm/s at a radius of ~50 km. Geostrophic currents derived from satellite altimetry data compare well with low-pass filtered Drifter velocities, with only a slight overestimation, which is expected as its maximum vorticity corresponds to a small Rossby number of ~0.6. Satellite ocean color images and some Drifters show that the eddy has an elliptical spiral structure. The looping tracks of the Drifters trapped in the eddy were analyzed using two statistical methods: least-squares ellipse fitting and wavelet ridge analysis, revealing a typical eccentricity of about 0.5, a wide range of inclination and a rotation period between 3 and 10 days. Clusters of Drifters on the northeastern limb of the eddy were also considered to estimate divergence and vorticity. The results indicate convergence (divergence) and downwelling (upwelling) at scales of 20–50 km near the northeastern (northwestern) edge of the eddy, in agreement with the quasi-geostrophic theory. Vertically, the eddy extends mostly down to 250 m depth, with a warm, low-salinity and low-density signature and with geostrophic currents near 50 cm/s in the top layer (down to ~80 m) reducing to less than 10 cm/s near 250 m. Near the surface, colder water is advected into it
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Removing Spurious Low-Frequency Variability in Drifter Velocities
2020Co-Authors: Rick Lumpkin, Luca Centurioni, Semyon A Grodsky, Marie-helene Rio, James A Carton, Dongkyu LeeAbstract:ABSTRACT Satellite-tracked drifting buoys of the Global Drifter Program have drogues, centered at 15-m depth, to minimize direct wind forcing and Stokes drift. Drogue presence has historically been determined from submergence or tether strain records. However, recent studies have revealed that a significant fraction of Drifters believed to be drogued have actually lost their drogues, a problem that peaked in the mid-2000s before the majority of Drifters in the global array switched from submergence to tether strain sensors. In this study, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion. Results indicate that the downwind slip of undrogued Drifters is approximately 50% higher than previously believed. The reanalyzed results no longer exhibit the dramatic and spurious interannual variations seen in the original data. These results, along with information from submergence/tether strain and transmission frequency variations, are now being used to conduct a systematic manual reevaluation of drogue presence for each Drifter in the post-1992 dataset
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Drifter technology and impacts for sea surface temperature sea level pressure and ocean circulation studies
2018Co-Authors: Luca CenturioniAbstract:The purpose of this chapter is twofold. First, we illustrate the technology used by the Lagrangian Drifters deployed by Global Drifter Program (GDP), which is the principal component of the Global Drifter Array; second, we review and summarize the most recent studies on the impact of Drifter data for calibration and validation of sea surface temperature (SST) satellite products, Numerical Weather Prediction (NWP) and climate studies, tropical cyclones (TCs)-ocean interaction and ocean circulation studies. Several types of Drifters are described, starting from the simplest configuration that measures SST and sea-level atmospheric pressure (SLP), continuing with special Drifters designed to measure sea surface salinity (SSS) and sea-level wind (SLW), and ending with air-deployable drifting thermistor chains that measure the temperature of the upper 150 m of the ocean, which are used to study the interaction of the ocean’s mixed layer with TCs. We also discuss the implications of the satellite telecommunication technology on the accuracy of Drifter’s geolocation and on the timeliness of the near real-time data stream.
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a global ocean observing system for measuring sea level atmospheric pressure effects and impacts on numerical weather prediction
Bulletin of the American Meteorological Society, 2017Co-Authors: Luca Centurioni, Andras Horanyi, Carla Cardinali, Etienne Charpentier, Rick LumpkinAbstract:AbstractSince 1994 the U.S. Global Drifter Program (GDP) and its international partners cooperating within the Data Buoy Cooperation Panel (DBCP) of the World Meteorological Organization (WMO) and the United Nations Education, Scientific and Cultural Organization (UNESCO) have been deploying Drifters equipped with barometers primarily in the extratropical regions of the world’s oceans in support of operational weather forecasting. To date, the impact of the Drifter data isolated from other sources has never been studied. This essay quantifies and discusses the effect and the impact of in situ sea level atmospheric pressure (SLP) data from the global Drifter array on numerical weather prediction using observing system experiments and forecast sensitivity observation impact studies. The in situ Drifter SLP observations are extremely valuable for anchoring the global surface pressure field and significantly contributing to accurate marine weather forecasts, especially in regions where no other in situ observ...
Gustavo Hernandezcarmona - One of the best experts on this subject based on the ideXlab platform.
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reproductive longevity of drifting kelp macrocystis pyrifera phaeophyceae in monterey bay usa 1
Journal of Phycology, 2006Co-Authors: Gustavo Hernandezcarmona, Brent B Hughes, Michael H GrahamAbstract:Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long-distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera Drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach-cast Drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow Drifter trajectories and to measure drifting speed. Experimental Drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio-tagged Drifters was 7.12km.day � 1 , suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890km ( � 363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter-hemispheric gene flow.
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reproductive longevity of drifting kelp macrocystis pyrifera phaeophyceae in monterey bay usa 1
Journal of Phycology, 2006Co-Authors: Gustavo Hernandezcarmona, Brent B Hughes, Michael H GrahamAbstract:Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long-distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera Drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach-cast Drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow Drifter trajectories and to measure drifting speed. Experimental Drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio-tagged Drifters was 7.12km.day � 1 , suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890km ( � 363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter-hemispheric gene flow.
Nikolai Maximenko - One of the best experts on this subject based on the ideXlab platform.
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pathways of marine debris derived from trajectories of lagrangian Drifters
Marine Pollution Bulletin, 2012Co-Authors: Nikolai Maximenko, Jan Hafner, Pearn P. NiilerAbstract:Abstract Global set of trajectories of satellite-tracked Lagrangian Drifters is used to study the dynamics of marine debris. A probabilistic model is developed to eliminate the bias in spatial distribution of Drifter data due to heterogeneous deployments. Model experiments, simulating long-term evolution of initially homogeneous Drifter array, reveal five main sites of Drifter aggregation, located in the subtropics and maintained by converging Ekman currents. The paper characterizes the geography and structure of the collection regions and discusses factors that determine their dynamics. A new scale R c = (4 k / |D |) 1/2 is introduced to characterize tracer distribution under competing effects of horizontal divergence D and diffusion k . Existence and locations of all five accumulation zones have been recently confirmed by direct measurements of microplastic at the sea surface.
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dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations
Geophysical Research Letters, 2003Co-Authors: Pearn P. Niiler, Nikolai Maximenko, James C McwilliamsAbstract:[1] The 1992–2002 time-mean absolute sea level distribution of the global ocean is computed for the first time from observations of near-surface velocity. For this computation, we use the near-surface horizontal momentum balance. The velocity observed by Drifters is used to compute the Coriolis force and the force due to acceleration of water parcels. The anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in Drifter data distribution. NCEP reanalysis winds are used to compute the force due to Ekman currents. The mean sea level gradient force, which closes the momentum balance, is integrated for mean sea level. We find that our computation agrees, within uncertainties, with the sea level computed from the geostrophic, hydrostatic momentum balance using historical mean density, except in the Antarctic Circumpolar Current. A consistent horizontally and vertically dynamically balanced, near-surface, global pressure field has now been derived from observations.
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near surface dynamical structure of the kuroshio extension
Journal of Geophysical Research, 2003Co-Authors: Pearn P. Niiler, Nikolai Maximenko, Gleb Panteleev, Toshio Yamagata, Donald B OlsonAbstract:[1] Lagrangian data from 657 SVP Drifters, CNES/Aviso (Archiving, Validation, and Interpretation of Satellite Oceanographic data) time variable satellite altimeter sea level anomaly and Levitus 98 hydrographic data are used to develop 0.25° spatial resolution maps of the mean and eddy circulations in the northwestern Pacific during the 1990s. Drifter velocities at 15 m depth and 200 m temperature data clearly indicate in the Kuroshio Extension (KE) jet two prominent meanders that culminate in a 300 km northward deflection east of the Shatsky Rise at 160°E. The interannual trends of Aviso mesoscale variance are absent along the path of the meandering KE jet. Three anticyclonic recirculations can be identified south or southeast of the Kuroshio, the southernmost around Daito Island being a new discovery. About 3% of the Drifters with drogues attached crossed the Kuroshio front. The Aviso currents are correlated at 0.8 with Drifter geostrophic velocity. The Aviso geostrophic currents are adjusted in amplitude to the contemporaneous Drifter observations and are further used to compute an unbiased mean geostrophic circulation and the quasi-geostrophic Reynolds' stresses in the KE region. The principal axes of the eddy Reynolds' stresses are oriented along the unbiased mean velocity vectors within the meandering KE jet. The time-mean horizontal momentum balance that includes both the mean and eddy momentum convergences is used to compute absolute sea level map and its uncertainty. At 145°E the 2000 m depth absolute dynamic height referenced to the sea level reveals a heretofore unknown 70 dynamic cm drop from 25° to 42°N.
