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"Ocean currents."
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Tracking trash : flotsam, jetsam, and the science of ocean motion
Describes the work of a man who tracks trash as it travels great distances by way of ocean currents.
Book
Mathematical Study of Degenerate Boundary Layers: A Large Scale Ocean Circulation Problem
This paper is concerned with a complete asymptotic analysis as
These boundary layers, which are the main center of interest of the
present paper, exhibit several types of peculiar behaviour. First, the size of the boundary layer on the western and eastern boundary,
which had already been computed by several authors, becomes formally very large as one approaches northern and southern portions of the
boudary, i.e. pieces of the boundary on which the normal is vertical. This phenomenon is known as geostrophic degeneracy. In order to
avoid such singular behaviour, previous studies imposed restrictive assumptions on the domain
Moreover,
when the domain
Eventually, the effect of boundary layers is non-local in several
aspects. On the first hand, for algebraic reasons, the boundary layer equation is radically different on the west and east parts of the
boundary. As a consequence, the Sverdrup equation is endowed with a Dirichlet condition on the East boundary, and no condition on the
West boundary. Therefore western and eastern boundary layers have in fact an influence on the whole domain
eBook
Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT
This paper analyzes the differences between ERA-Interim and ERA5 surface winds fields relative to Advanced Scatterometer (ASCAT) ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress-equivalent winds (U10S) and air–sea relative motion using ocean current velocities. In terms of instantaneous root mean square (rms) wind speed agreement, ERA5 winds show a 20 % improvement relative to ERA-Interim and a performance similar to that of currently operational ECMWF forecasts. ERA5 also performs better than ERA-Interim in terms of mean and transient wind errors, wind divergence and wind stress curl biases. Yet, both ERA products show systematic errors in the partition of the wind kinetic energy into zonal and meridional, mean and transient components. ERA winds are characterized by excessive mean zonal winds (westerlies) with too-weak mean poleward flows in the midlatitudes and too-weak mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic in midlatitudes and high latitudes, with implications for Ekman upwelling estimates, and lacks detail in the representation of sea surface temperature (SST) gradient effects (along the equatorial cold tongues and Western Boundary Current (WBC) jets) and mesoscale convective airflows (along the Intertropical Convergence Zone and the warm flanks for the WBC jets). It is conjectured that large-scale mean wind biases in ERA are related to their lack of high-frequency (transient wind) variability, which should be promoting residual meridional circulations in the Ferrel and Hadley cells.
Journal Article
SWOT Enhances Small‐Scale Eddy Detection in the Mediterranean Sea
Ocean currents are crucial in regulating Earth's climate, with a significant impact in the distribution of ocean properties. During the Calibration/Validation phase of the Surface Water and Ocean Topography (SWOT) satellite mission, we performed a high‐resolution, multi‐platform experiment to evaluate SWOT's ability to resolve small‐scale features, focusing on a ∼25 km‐radius anticyclonic eddy in the Western Mediterranean Sea. Acoustic Doppler Current Profiler (ADCP) recorded maximum velocities of 30 cm/s at 155 m depth and underwater glider data identified biconvex isopycnals, classifying the eddy as intrathermocline. SWOT successfully captured the sea level signal and surface geostrophic currents of the eddy, showing notable error reduction over conventional altimetry: 24% in sea level representation compared to glider observations, and 35% and 31% in horizontal velocity magnitude compared to Acoustic Doppler Current Profiler and drifter measurements, respectively. This study highlights SWOT's potential in resolving small‐scale ocean dynamics.
Journal Article
Five million years of Antarctic Circumpolar Current strength variability
The Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability
1
–
3
. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity
4
. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial–interglacial cycles
5
–
8
, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling
9
and increasing global ice volume
10
. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings
11
–
13
. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability
14
. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO
2
during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming.
The strength of the Antarctic Circumpolar Current, as traced in sediment cores from the Pacific Southern Ocean, shows no linear long-term trend over the past 5.3 Myr; instead, the strongest flow occurs consistently in warmer-than-present intervals.
Journal Article
Statistical downscaling reproduces high-resolution ocean transport for particle tracking in the Bering Sea
Understanding ocean transport is critical for applications ranging from fisheries to chemical plume tracking and carbon dioxide removal modeling. However, available hydrodynamic data often lack the spatial resolution needed for effective transport simulations. We apply statistical downscaling to coarse-resolution ocean reanalysis and atmospheric wind data, reconstructing fine-scale fields validated against high-resolution dynamic models in the Bering Sea. This enables the prediction of transport patterns without the need to run high resolution physics simulations, saving computational costs and time. We examined five years of high-resolution, statistically downscaled ocean currents and surface winds and found that the correlation of ocean current and wind components with GLORYS and ERA5 reanalysis models were r = 0.87 and r = 0.98. The Liu-mean skill score was 0.75 for ocean current velocity. Okubo–Weiss analyses showed comparable vorticity and shear between downscaled and dynamical models. The Finite-time Layupanov Exponent analysis showed consistent Lagrangian Cohesive Structures across datasets. Multi-year particle tracking using both downscaled and reanalysis forcing showed consistent relative separation distances with mean Bhattacharyya coefficient of 0.720 ± 0.133. The demonstrated parity in dispersal patterns indicates statistically downscaled approaches can substitute dynamical models for large-scale applications. Future work should validate these results across diverse oceanographic regimes and incorporate biogeochemical feedback mechanisms.
Journal Article
Influence of Kuroshio Extension’s sea surface temperature variability on the North Pacific atmosphere and Pacific Decadal Precession
Recent research has revealed links between a quasi-decadal mode of climate variability over the North Pacific – the Pacific Decadal Precession (PDP) – and the North Pacific’s western boundary current’s extension – the Kuroshio Extension (KE). It is suggested that on decadal time scales the PDP both responds to and influences the KE variability. A question yet to be answered is whether it is the large-scale or the mesoscale variations of the KE region that link with the PDP evolution. Using high-resolution sea surface temperature data (1981–2018) from the global ocean Operational Sea Surface Temperature (SST) and Sea Ice Analysis, low-resolution Extended Reconstructed SST (ERSST) version 3b data (1949–2018), geopotential height reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) we find that it is the large-scale variations in the KE region that correlate best with the PDP-like response in the overlying and downstream atmosphere as compared to the mesoscale variations. In particular, the second mode of the large-scale KE region, which is characterized by the warming (cooling) of the ocean south (north) of the KE, sets up a PDP-like north-south atmospheric pressure dipole over the North Pacific Ocean by altering the large-scale baroclinicity of the atmosphere and zonal intensification of the subtropical jet stream. In turn, there is a reduction in the zonal propagation of stationary wave energy and an enhancement of the climatological zonal wave heights over North America, which results in a downstream response over the North American continent and the formation of a subsequent east-west pressure dipole over the North Pacific and North American continent. As a result, there is a strong correlation between large-scale SST variations in the KE region and the evolution of the PDP over the next three years.
Journal Article
Scale-Model Experiments for the Surface Wave Influence on a Submerged Floating Ocean-Current Turbine
In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a marine current, the resulting rotor torque needs to be canceled. Therefore, the proposed turbine is designed with a float at its top and a counterweight at its bottom. Thus far, we have verified the turbine stability and blade performance through towing experiments. As the next step, we constructed a scale-model turbine to confirm the mooring system. This experiment was performed at a circulating water channel with wave-making facilities. The influence of waves on the floating body was also investigated. In this paper, we report the behavior of the scale-model turbine moored to the tank bottom and discuss the influence of surface waves.
Journal Article
Effects of Equatorial Ocean Current Bias on Simulated El Niño Pattern in CMIP6 Models
This study utilized the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to examine the simulations of equatorial ocean currents and explore their substantial influences on the systematic bias of westward‐extended sea surface temperature anomalies (SSTA) pattern during El Niño. The results show that models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state. It tends to suppress the equatorial eastward ocean current anomalies with their maximum centering over the equatorial western Pacific in the El Niño developing phase. As a consequence, an overestimated zonal advective feedback toward the maritime continent exists, subsequently inducing the biased westward extension of SSTA pattern. Our results show that the mean‐state performance of equatorial ocean currents plays a key role on simulations of El Niño evolution in CMIP6 models. Plain Language Summary El Niño is the warm phase of El Niño–Southern Oscillation, known as a coupled air–sea phenomenon with considerable interannual variability in the tropics. In recent decades, many climate models have been developed to help us better understand the potential dynamics of El Niño. This study emphasizes the role of dynamical processes related to ocean currents in affecting the behavior of El Niño patterns in a series of the latest released CMIP6 climate models. We find that models have a relatively large bias in simulating the equatorial ocean currents in the Pacific. With an extremely strong equatorial zonal current in mean‐state field, the maximum of zonal current anomalies tends to shift toward the equatorial western Pacific and enhances the corresponding oceanic feedback mechanism, which substantially contributes to the overestimated sea surface temperature anomalies during El Niño evolution. Key Points The Coupled Model Intercomparison Project Phase 6 (CMIP6) models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state Overestimated zonal advective feedback in the warm pool region is the dominant factor for the westward extension of El Niño pattern Mean‐state performance of equatorial ocean current field plays a key role on the simulations of El Niño evolution in CMIP6 models
Journal Article