Is the Vertical Variability of the Ocean in Santos Bight, Brazil, Dominated by the Western Boundary Current Meanders?

2012 ◽  
Author(s):  
Wellington Ceccopieri ◽  
Ilson C. A. da Silveira
Keyword(s):  
Large Scale ◽  
Seawater Temperature ◽  
Great Part ◽  
Shelf Break ◽  
Data Series ◽  
Western Boundary ◽  
Baroclinic Mode ◽  
Oceanic Circulation ◽  
Current Profile ◽  
Boundary Current

The Brazil Current (CB) flows southwestward as vertically stratified and organized western boundary jet in the Brazilian shelf-break region ranging from 20–40° S, where the CB’s mass transport grows vertically. This geographical band show intense mesoescale activity due to passageway of eddies and meanders, superimposed over oceanic large-scale recirculation features which influence the oceanic circulation in the Santos Bight Pre-salt cluster area 300 km offshore. Based on 2-year observed data series of an oceanographic mooring array at Lula Field, and based on repeated hydrographic data (seawater temperature, salinity and N2 profiles) we used statistical and dynamical orthogonal modes in order to approach the local vertical current profile variability. We verified that it is 85 % explained by EOF-1. This variability is essentially of 1st baroclinic mode. Great part of it occupies the first 400–600 m water depth, with no predominant direction. We also found remarkable water column seasonal stratification. Albeit of relative weaker mean flows (0.1–0.2 m s−1), the study area is eddy dominated which are geostrophically adjusted to the 1st baroclinic mode. Furthermore, we observed that the significant directional variability over the São Paulo Plateau occurs far away from the mean current jets that flow parallel to the continental shelf-break geometry.

Topographic Rossby Waves in the Abyssal South China Sea

2021 ◽  
Author(s):  
QI QUAN ◽  
ZHONGYA CAI ◽  
GUANGZHEN JIN ◽  
ZHIQIANG LIU
Keyword(s):  
South China Sea ◽  
Group Velocity ◽  
South China ◽  
Large Scale ◽  
Rossby Waves ◽  
Western Boundary ◽  
Horizontal Shear ◽  
Boundary Current ◽  
China Sea ◽  
Topographic Rossby Waves

AbstractTopographic Rossby waves (TRWs) in the abyssal South China Sea (SCS) are investigated using observations and high-resolution numerical simulations. These energetic waves can account for over 40% of the kinetic energy (KE) variability in the deep western boundary current and seamount region in the central SCS. This proportion can even reach 70% over slopes in the northern and southern SCS. The TRW-induced currents exhibit columnar (i.e., in-phase) structure in which the speed increases downward. Wave properties such as the period (5–60 days), wavelength (100–500 km), and vertical trapping scale (102–103 m) vary significantly depending on environmental parameters of the SCS. The TRW energy propagates along steep topography with phase propagation offshore. TRWs with high frequencies exhibit a stronger climbing effect than low-frequency ones and hence can move further upslope. For TRWs with a certain frequency, the wavelength and trapping scale are dominated by the topographic beta, whereas the group velocity is more sensitive to the internal Rossby deformation radius. Background circulation with horizontal shear can change the wavelength and direction of TRWs if the flow velocity is comparable to the group velocity, particularly in the central, southern, and eastern SCS. A case study suggests two possible energy sources for TRWs: mesoscale perturbation in the upper layer and large-scale background circulation in the deep layer. The former provides KE by pressure work, whereas the latter transfers the available potential energy (APE) through baroclinic instability.

scholarly journals Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT

Ocean Science ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 831-852 ◽  
Author(s):  
Maria Belmonte Rivas ◽  
Ad Stoffelen
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Atmospheric Stability ◽  
Ocean Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Meridional Winds ◽  
Mesoscale Convective ◽  
Transient Wind

Abstract. 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.

scholarly journals 100 Years of the Ocean General Circulation

2018 ◽  
Vol 59 ◽  
pp. 7.1-7.32 ◽  
Author(s):  
Carl Wunsch ◽  
Raffaele Ferrari
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Large Scale ◽  
Time Dependent ◽  
Steady Flows ◽  
Oceanic Circulation ◽  
Boundary Current ◽  
Geophysical Fluid Dynamics ◽  
The Past ◽  
The Tropics

Abstract The central change in understanding of the ocean circulation during the past 100 years has been its emergence as an intensely time-dependent, effectively turbulent and wave-dominated, flow. Early technologies for making the difficult observations were adequate only to depict large-scale, quasi-steady flows. With the electronic revolution of the past 50+ years, the emergence of geophysical fluid dynamics, the strongly inhomogeneous time-dependent nature of oceanic circulation physics finally emerged. Mesoscale (balanced), submesoscale oceanic eddies at 100-km horizontal scales and shorter, and internal waves are now known to be central to much of the behavior of the system. Ocean circulation is now recognized to involve both eddies and larger-scale flows with dominant elements and their interactions varying among the classical gyres, the boundary current regions, the Southern Ocean, and the tropics.

scholarly journals Mixing Nonlocality and Mixing Anisotropy in an Idealized Western Boundary Current Jet

2017 ◽  
Vol 47 (12) ◽  
pp. 3015-3036 ◽  
Author(s):  
Ru Chen ◽  
Stephanie Waterman
Keyword(s):  
Large Scale ◽  
Eddy Diffusivity ◽  
Western Boundary Current ◽  
Wave Radiation ◽  
Western Boundary ◽  
Equilibration Time ◽  
Boundary Current ◽  
Jet Mixing ◽  
Velocity Magnitude ◽  
Axis Length

AbstractMotivated by the key role of western boundary currents in shaping water mass distribution and gyre water exchanges, this study characterizes mixing in an idealized western boundary current jet using a barotropic quasigeostrophic model with numerical particles deployed. Both the nonlocality of mixing, depicted by nonlocality ellipses, and mixing anisotropy, depicted by mixing ellipses, are estimated. Mixing is more nonlocal within the jet compared to the jet flanks. In general, the size of nonlocality ellipses, a metric of the degree of mixing nonlocality, scales with the eddy velocity magnitude and the equilibration time for diffusivity. The tilt and eccentricity of the nonlocality ellipses, a characterization of the anisotropy of mixing nonlocality, agree with those of momentum flux ellipses in the regions where mixing nonlocality is small. Mixing ellipse characteristics are flow regime dependent. In regions dominated by wave radiation, the mixing ellipses align with the contours of the wave streamfunction and are very anisotropic. Inside the recirculations, however, the mixing ellipses are nearly isotropic. Mixing ellipses are zonally elongated in the jet upstream because of the suppression of cross-jet mixing by the jet and the anisotropy of eddy velocity, and they can have negative minor axis length in the jet downstream, indicating negative cross-jet eddy diffusivity, which is consistent with upgradient eddy fluxes there. Thus, despite significant spatial heterogeneity in mixing nonlocality and anisotropy, in this idealized system at least, spatial patterns in these diagnostics tend to be relatively large scale and tied to larger-scale dynamics. The implications of these results to eddy parameterization and jet dynamics are discussed.

scholarly journals The Effects of Mesoscale Ocean–Atmosphere Coupling on the Large-Scale Ocean Circulation

2009 ◽  
Vol 22 (15) ◽  
pp. 4066-4082 ◽  
Author(s):  
Andrew Mc C. Hogg ◽  
William K. Dewar ◽  
Pavel Berloff ◽  
Sergey Kravtsov ◽  
David K. Hutchinson
Keyword(s):  
Spatial Scale ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ocean Model ◽  
Small Scale ◽  
Western Boundary ◽  
Ekman Pumping ◽  
Boundary Current ◽  
Ocean Atmosphere ◽  
Gyre Circulation

Abstract Small-scale variation in wind stress due to ocean–atmosphere interaction within the atmospheric boundary layer alters the temporal and spatial scale of Ekman pumping driving the double-gyre circulation of the ocean. A high-resolution quasigeostrophic (QG) ocean model, coupled to a dynamic atmospheric mixed layer, is used to demonstrate that, despite the small spatial scale of the Ekman-pumping anomalies, this phenomenon significantly modifies the large-scale ocean circulation. The primary effect is to decrease the strength of the nonlinear component of the gyre circulation by approximately 30%–40%. This result is due to the highest transient Ekman-pumping anomalies destabilizing the flow in a dynamically sensitive region close to the western boundary current separation. The instability of the jet produces a flux of potential vorticity between the two gyres that acts to weaken both gyres.

scholarly journals Sea Level Expression of Intrinsic and Forced Ocean Variabilities at Interannual Time Scales

2011 ◽  
Vol 24 (21) ◽  
pp. 5652-5670 ◽  
Author(s):  
Thierry Penduff ◽  
Mélanie Juza ◽  
Bernard Barnier ◽  
Jan Zika ◽  
William K. Dewar ◽  
...  
Keyword(s):  
Sea Level ◽  
Time Scales ◽  
General Circulation ◽  
Large Scale ◽  
Full Range ◽  
Circulation Model ◽  
Global Ocean ◽  
Western Boundary ◽  
Intrinsic Variability ◽  
Boundary Current

Abstract This paper evaluates in a realistic context the local contributions of direct atmospheric forcing and intrinsic oceanic processes on interannual sea level anomalies (SLAs). A ¼° global ocean–sea ice general circulation model, driven over 47 yr by the full range of atmospheric time scales, is quantitatively assessed against altimetry and shown to reproduce most observed features of the interannual SLA variability from 1993 to 2004. Comparing this simulation with a second driven only by the climatological annual cycle reveals that the intrinsic part of the total interannual SLA variance exceeds 40% over half of the open-ocean area and exceeds 80% over one-fifth of it. This intrinsic contribution is particularly strong in eddy-active regions (more than 70%–80% in the Southern Ocean and western boundary current extensions) as predicted by idealized studies, as well as within the 20°–35° latitude bands. The atmosphere directly forces most of the interannual SLA variance at low latitudes and in most midlatitude eastern basins, in particular north of about 40°N in the Pacific. The interannual SLA variance is almost entirely due to intrinsic processes south of the Antarctic Circumpolar Current in the Indian Ocean sector, while half of this variance is forced by the atmosphere north of it. The same simulations were performed and analyzed at 2° resolution as well: switching to this laminar regime yields a comparable forced variability (large-scale distribution and magnitude) but almost suppresses the intrinsic variability. This likely explains why laminar ocean models largely underestimate the interannual SLA variance.

scholarly journals FIFTY YEARS AGO YU. A. IVANOV WITH HIS COLLEAGUES DISCOVERED THE ANTILLES-GUIANA CURRENT

2019 ◽  
Vol 47 (2) ◽  
pp. 64-75
Author(s):  
V.G. Neiman
Keyword(s):  
Large Scale ◽  
Current System ◽  
Western Boundary ◽  
Boundary Current ◽  
Shirshov Institute ◽  
Actual System ◽  
Direct Measurements ◽  
History Of ◽  
Academy Of Sciences ◽  
First Time

A brief history of the Antilles-Guiana Current discovery during cruise 5 of the scientific research vessel (R/V) “Akademik Kurchatov” in 1969 in the Atlantic Ocean is presented. This expedition of the Shirshov Institute of Oceanology of the USSR Academy of Sciences was targeted for experimental study of the Western Boundary Current System in the tropical Atlantic. The previous studies in this region revealed signs of the Southern flow within the system, which overall meridional velocity component was of the Northern direction. However, the traces of Southern currents in all such cases were usually interpreted as a manifestation of a large-scale eddy activity in the velocity field of the main North-Western water transport. In the expedition of 1969, for the first time in the Russian oceanography a non-trivial method for the direct measurements of a current velocity was applied. It is based on the results of an immediate preliminary hydrographic survey of the area, which proposed by Y.A. Ivanov. This method has made possible to determine in details the actual system of the Western boundary flows, in which the previously unknown to science the Antilles-Guiana Current was discovered. The other Russian expeditions, which have been carried out in 1970 and 1972 during 9 and 12 cruises of the R/V “Akademik Kurchatov”, revealed the interannual stability of this flow, including the mass transport, approximately equal to 30 Sv, i.e. almost half of the volume of water carried by the Gulf Stream.

scholarly journals Observations of Entry and Exit of Potential Vorticity at the Sea Surface

2009 ◽  
Vol 39 (9) ◽  
pp. 2280-2294 ◽  
Author(s):  
Arnaud Czaja ◽  
Ute Hausmann
Keyword(s):  
Potential Vorticity ◽  
Sea Surface ◽  
Western Boundary ◽  
Oceanic Circulation ◽  
Entry And Exit ◽  
Boundary Current ◽  
The North ◽  
The Pacific ◽  
Low Latitudes ◽  
The North Pacific

Abstract Although potential vorticity (PV) is central to many theories of the oceanic circulation, the entry–exit of PV at the sea surface has not been thoroughly discussed from an observational perspective. After clarifying the notion of “PV entry and exit,” and the mechanisms responsible for it, a climatology of this quantity for the Northern Hemisphere is presented. It is found that surface PV loss over western boundary current regions and their interior extension is a robust feature over the North Pacific and Atlantic basins. At high latitudes, mechanical and diabatic effects act in concert in the North Atlantic to drive the net PV exit. In the Pacific, however, these effects oppose each other and the net entry–exit of PV is more uncertain. At low latitudes, surface winds are found to be particularly important in setting the surface PV exit in the Pacific, equatorward of the intertropical convergence zone.

scholarly journals Detecting flow features in scarce trajectory data using networks derived from symbolic itineraries: an application to surface drifters in the North Atlantic

2020 ◽  
Vol 27 (4) ◽  
pp. 501-518 ◽  
Author(s):  
David Wichmann ◽  
Christian Kehl ◽  
Henk A. Dijkstra ◽  
Erik van Sebille
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Boundary ◽  
Boundary Current ◽  
Trajectory Data ◽  
Surface Transport ◽  
The North ◽  
The North Atlantic ◽  
Surface Drifters ◽  
Double Gyre

Abstract. The basin-wide surface transport of tracers such as heat, nutrients and plastic in the North Atlantic Ocean is organized into large-scale flow structures such as the Western Boundary Current and the Subtropical and Subpolar gyres. Being able to identify these features from drifter data is important for studying tracer dispersal but also for detecting changes in the large-scale surface flow due to climate change. We propose a new and conceptually simple method to detect groups of trajectories with similar dynamical behaviour from drifter data using network theory and normalized cut spectral clustering. Our network is constructed from conditional bin-drifter probability distributions and naturally handles drifter trajectories with data gaps and different lifetimes. The eigenvalue problem of the respective Laplacian can be replaced by a singular value decomposition of a related sparse data matrix. The construction of this matrix scales with O(NM+Nτ), where N is the number of particles, M the number of bins and τ the number of time steps. The concept behind our network construction is rooted in a particle's symbolic itinerary derived from its trajectory and a state space partition, which we incorporate in its most basic form by replacing a particle's itinerary by a probability distribution over symbols. We represent these distributions as the links of a bipartite graph, connecting particles and symbols. We apply our method to the periodically driven double-gyre flow and successfully identify well-known features. Exploiting the duality between particles and symbols defined by the bipartite graph, we demonstrate how a direct low-dimensional coarse definition of the clustering problem can still lead to relatively accurate results for the most dominant structures and resolve features down to scales much below the coarse graining scale. Our method also performs well in detecting structures with incomplete trajectory data, which we demonstrate for the double-gyre flow by randomly removing data points. We finally apply our method to a set of ocean drifter trajectories and present the first network-based clustering of the North Atlantic surface transport based on surface drifters, successfully detecting well-known regions such as the Subpolar and Subtropical gyres, the Western Boundary Current region and the Caribbean Sea.

scholarly journals Assemblages of Gelatinous Zooplankton in Mesoscale Oceanographic Features in the Tropical-Temperate Transition Zone of a Western Boundary Current

2021 ◽  
Author(s):  
Kylie Pitt ◽  
Jonathan W. Lawley ◽  
Charles Hinchliffe ◽  
Paloma A. Matis ◽  
Iain M. Suthers
Keyword(s):  
Continental Shelf ◽  
Spatial Dynamics ◽  
Gelatinous Zooplankton ◽  
Shelf Break ◽  
Cyclonic Eddy ◽  
Western Boundary ◽  
Boundary Current ◽  
Tasman Sea ◽  
Anticyclonic Eddies ◽  
Zooplankton Communities

Abstract Boundary currents generate cyclonic and anticyclonic eddies, which strongly influence the composition of plankton communities and their spatial dynamics. We explored the gelatinous zooplankton communities where the East Australian Current (EAC) intensifies between 25-31°S, forming a dynamic eddy field at a tropical/temperate boundary. Five types of mesoscale features including the EAC were sampled: the adjacent continental shelf, a transient upwelling feature at the shelf break, a cyclonic frontal eddy which had entrained shelf water and a larger cyclonic eddy that had originated in the Tasman Sea. Forty-two gelatinous taxa were sampled from 62 plankton tows, including 24 cnidarians (9 hydromedusae, 14 siphonophores, 1 scyphozoan), 5 ctenophores and 12 thaliaceans. Assemblages of gelatinous zooplankton differed significantly among oceanographic features but were dominated by the salp, Salpa fusiformis, which comprised 66% of the overall catch. Abundances of gelatinous zooplankton were lowest in the EAC, the shelf break upwelling feature and over the continental shelf, which at the time sampled was flooded by a coastal incursion of the EAC. Abundances were greatest in the two cyclonic eddies and increased four-fold in the Tasman Sea cyclonic eddy over the three times it was sampled, highlighting the importance of cyclonic eddies in driving production of gelatinous zooplankton.

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