Overlooked current estimation biases arising from the Lagrangian Argo trajectory derivation method

2021 ◽  
Author(s):  
Tianyu Wang ◽  
Yan Du ◽  
Minyang Wang
Keyword(s):  
Ocean Model ◽  
Ocean Dynamics ◽  
Western Boundary ◽  
Boundary Current ◽  
Current Estimation ◽  
Quantitative Metrics ◽  
Circumpolar Current ◽  
Derivation Method ◽  
Jet Interactions ◽  
Reference Layer

AbstractAn Argo simulation system is used to provide synthetic Lagrangian trajectories based on the Estimating the Circulation and Climate of the Ocean model, Phase II (ECCO2). In combination with ambient Eulerian velocity at the reference layer (1000 m) from the model, quantitative metrics of the Lagrangian trajectory-derived velocities are computed. The result indicates that the biases induced by the derivation algorithm are strongly linked with ocean dynamics. In low latitudes, Ekman currents and vertically sheared geostrophic currents influence both the magnitude and the direction of the derivation velocity vectors. The maximal shear-induced biases exist near the equator with the amplitudes reaching up to about 1.2 cm s-1. The angles of the shear biases are pronounced in the low latitude oceans, ranging from -8° to 8°. Specifically, the study shows an overlooked bias from the float drifting motions that mainly occurs in the western boundary current and Antarctic circumpolar current (ACC) regions. In these regions, a recently reported horizontal acceleration measured via Lagrangian floats is significantly associated with the strong eddy-jet interactions. The acceleration could induce an overestimation of Eulerian current velocity magnitudes. For the common Argo floats with a 9-day float parking period, the derivation speed biases induced by velocity acceleration would be as large as 3 cm s-1, approximately 12% of the ambient velocity. It might have implications to map the mean mid-depth ocean currents from Argo trajectories, as well as understand the dynamics of eddy-jet interactions in the ocean.

scholarly journals The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model

2016 ◽  
Vol 9 (10) ◽  
pp. 3655-3670 ◽  
Author(s):  
Helene T. Hewitt ◽  
Malcolm J. Roberts ◽  
Pat Hyder ◽  
Tim Graham ◽  
Jamie Rae ◽  
...  
Keyword(s):  
High Resolution ◽  
Coupled Model ◽  
Ocean Model ◽  
The Body ◽  
Western Boundary ◽  
Coupled Models ◽  
Technical Developments ◽  
Enhanced Resolution ◽  
Circumpolar Current ◽  
The Impact

Abstract. There is mounting evidence that resolving mesoscale eddies and western boundary currents as well as topographically controlled flows can play an important role in air–sea interaction associated with vertical and lateral transports of heat and salt. Here we describe the development of the Met Office Global Coupled Model version 2 (GC2) with increased resolution relative to the standard model: the ocean resolution is increased from 1/4 to 1/12° (28 to 9 km at the Equator), the atmosphere resolution increased from 60 km (N216) to 25 km (N512) and the coupling period reduced from 3 hourly to hourly. The technical developments that were required to build a version of the model at higher resolution are described as well as results from a 20-year simulation. The results demonstrate the key role played by the enhanced resolution of the ocean model: reduced sea surface temperature (SST) biases, improved ocean heat transports, deeper and stronger overturning circulation and a stronger Antarctic Circumpolar Current. Our results suggest that the improvements seen here require high resolution in both atmosphere and ocean components as well as high-frequency coupling. These results add to the body of evidence suggesting that ocean resolution is an important consideration when developing coupled models for weather and climate applications.

Ship Routing Based on the Kuroshio Current

2017 ◽  
Author(s):  
Chen Chen ◽  
Masashi Kashiwagi
Keyword(s):  
North Pacific Ocean ◽  
Kuroshio Current ◽  
Ocean Model ◽  
Ocean Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Ship Maneuvering ◽  
Ship Routing ◽  
Ship Navigation ◽  
The Kuroshio

As a strong western-boundary current, the Kuroshio Current has significant effects on the ship navigation in the East China Sea (ECS). To quantitatively know more about its influence, we present simulations of the ocean current in the North Pacific Ocean using the well-known Princeton Ocean Model (POM). The high-resolution current distributions could be applied to conduct numerical simulations of the ship navigation, which utilized a ship maneuvering model known as the Mathematical Maneuvering Group (MMG). Calculation of a container ship as well as a training ship have been conducted. The simulation results of both ships can show the significant effects of ocean currents on ship’s drifting as well as speed change, which could be used to optimize cost of both fuel and time by properly utilizing the current in ship routing.

scholarly journals Decadal Response of Global Circulation to Southern Ocean Zonal Wind Stress Perturbation

2009 ◽  
Vol 39 (8) ◽  
pp. 1888-1904 ◽  
Author(s):  
Barry A. Klinger ◽  
Carlos Cruz
Keyword(s):  
Southern Ocean ◽  
Southern Hemisphere ◽  
Time Scales ◽  
Wind Stress ◽  
Volume Transport ◽  
Ocean Model ◽  
Return Flow ◽  
Western Boundary ◽  
Boundary Current ◽  
Wind Variability

Abstract A substantial component of North Atlantic Deep Water formation may be driven by westerly wind stress over the Southern Ocean. Variability of this wind stress on decadal time scales may lead to circulation variability far from the forcing region. The Hybrid Coordinate Ocean Model (HYCOM), a numerical ocean model, is used to investigate the spatial patterns and the time scales associated with such wind variability. The evolution of circulation and density anomalies is observed by comparing one 80-yr simulation, forced in part by relatively strong Southern Hemisphere westerlies, with a simulation driven by climatological wind. The volume transport anomaly takes about 10 yr to reach near-full strength in the entire Southern Hemisphere; however, in the Northern Hemisphere, it grows for the duration of the run. The Southern Hemisphere Indo-Pacific volume transport anomaly is about twice the strength of that found in the Atlantic. In the thermocline, water exits the southern westerlies belt in a broad flow that feeds a western boundary current (WBC) in both the Atlantic and Pacific Oceans. These WBCs in turn feed an Indonesian Throughflow from the Pacific and cyclonic gyres in the far north, which are broadly consistent with the Stommel–Arons theory. The deep return flow in each hemisphere is strongly affected by deep-sea ridges, which leads to a number of midocean “WBCs.” The wind perturbation causes isopycnals to sink over most of the basin. After about 20 yr, this sinking is very roughly uniform with latitude, though it varies by basin.

scholarly journals Detecting unstable structures and controlling error growth by assimilation of standard and adaptive observations in a primitive equation ocean model

2006 ◽  
Vol 13 (1) ◽  
pp. 67-81 ◽  
Author(s):  
F. Uboldi ◽  
A. Trevisan
Keyword(s):  
Forecast Error ◽  
Ocean Model ◽  
Space Distribution ◽  
Western Boundary ◽  
Error Growth ◽  
Boundary Current ◽  
Primitive Equation ◽  
Near Surface ◽  
Observational Network ◽  
Deep Layers

Abstract. Oceanic and atmospheric prediction is based on cyclic analysis-forecast systems that assimilate new observations as they become available. In such observationally forced systems, errors amplify depending on their components along the unstable directions; these can be estimated by Breeding on the Data Assimilation System (BDAS). Assimilation in the Unstable Subspace (AUS) uses the available observations to estimate the amplitude of the unstable structures (computed by BDAS), present in the forecast error field, in order to eliminate them and to control the error growth. For this purpose, it is crucial that the observational network can detect the unstable structures that are active in the system. These concepts are demonstrated here by twin experiments with a large state dimension, primitive equation ocean model and an observational network having a fixed and an adaptive component. The latter consists of observations taken each time at different locations, chosen to target the estimated instabilities, whose positions and features depend on the dynamical characteristics of the flow. The adaptive placement and the dynamically consistent assimilation of observations (both relying upon the estimate of the unstable directions of the data-forced system), allow to obtain a remarkable reduction of errors with respect to a non-adaptive setting. The space distribution of the positions chosen for the observations allows to characterize the evolution of instabilities, from deep layers in western boundary current regions, to near-surface layers in the eastward jet area.

scholarly journals Hysteresis and Dynamics of a Western Boundary Current Flowing by a Gap Forced by Impingement of Mesoscale Eddies

2011 ◽  
Vol 41 (5) ◽  
pp. 878-888 ◽  
Author(s):  
Dongliang Yuan ◽  
Zheng Wang
Keyword(s):  
Hopf Bifurcation ◽  
Mesoscale Eddies ◽  
Small Deformation ◽  
Ocean Model ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Periodic Regime ◽  
Boundary Current ◽  
Nonlinear Hysteresis ◽  
Vorticity Balance

Abstract Hysteresis of a western boundary current (WBC) flowing by a wide gap of a western boundary and the dynamics of the WBC variations associated with the impingement of mesoscale eddies from the eastern side of the gap are studied using a 1.5-layer reduced-gravity quasigeostrophic ocean model. The study focuses on two issues not covered by existing studies: the effects of finite baroclinic deformation radii and time dependence perturbed by mesoscale eddies. The results of the study show that the hysteresis of the WBC of finite baroclinic deformation radii is not controlled by multiple steady-state balances of the quasigeostrophic vorticity equation. Instead, the hysteresis is controlled by the periodic penetrating and the leaping regimes of the vorticity balance. The regime of the vorticity balance inside the gap is dependent on the history of the WBC evolution, which gives rise to the hysteresis of the WBC path. Numerical experiments have shown that the parameter domain of the hysteresis is not sensitive to the baroclinic deformation radius. However, the domain of the periodic solution, which is determined by the lower Hopf bifurcation of the nonlinear system, is found to be sensitive to the magnitude of the baroclinic deformation radius. The lower Hopf bifurcation from steady penetration to periodic penetration is found to occur at lower Reynolds numbers for larger deformation radii. In general, the lower Hopf bifurcation stays outside the hysteresis domain of the Reynolds number. However, for very small deformation radii, the lower Hopf bifurcation falls inside the hysteresis domain, which results in the transition from the leaping to the penetrating regimes of the WBC to skip the periodic regime and hence the disappearance of the upper Hopf bifurcation. Mesoscale eddies approaching the gap from the eastern basin are found to have significant impact on the WBC path inside the gap when the WBC is at a critical state along the hysteresis loop. Cyclonic (anticyclonic) eddies play the role of reducing (enhancing) the inertial advection of vorticity in the vicinity of the gap so that transitions of the WBC path from the leaping (periodic penetrating) to the periodic penetrating (leaping) regimes are induced. In addition, cyclonic eddies are able to induce transitions of the WBC from the periodic penetrating to the leaping regimes through enhancing the meridional advection by its right fling. The transitions are irreversible because of the nonlinear hysteresis and are found to be sensitive to the strength, size, and approaching path of the eddy.

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 Ocean Dynamics and Topographic Upwelling Around the Aracati Seamount - North Brazilian Chain From in situ Observations and Modeling Results

2021 ◽  
Vol 8 ◽  
Author(s):  
Marcus Silva ◽  
Moacyr Araujo ◽  
Fábio Geber ◽  
Carmen Medeiros ◽  
Julia Araujo ◽  
...  
Keyword(s):  
Euphotic Zone ◽  
Ocean Dynamics ◽  
Upstream Region ◽  
Western Boundary ◽  
Austral Winter ◽  
Boundary Current ◽  
Equatorial Atlantic ◽  
Austral Spring ◽  
Surface Gravity Wave ◽  
North Brazil

The hydrodynamics and the occurrence of topographic upwelling around the northern Brazilian seamount chain were investigated. Meteorological and physical oceanographic data collected under the REVIZEE-NE Program cruises around the Aracati Bank, the major and highly productive seamount in the area, were analyzed and used to force and validate simulations using the 3D Princeton Ocean Model (3D POM). The Tropical Water mass in the top 150-m layer and the South Atlantic Central Water (SACW) beneath it and down to a depth of 670 m was present. The thickness of the barrier layer varied seasonally, being thinner (2 m) during the austral spring (October–December) and thicker (20 m) during the austral autumn (April–June) when winds were stronger. The surface mixed and isothermal layers in the austral winter (July–September) were located at depths of 84 and 96 m, respectively. During the austral spring, those layers were located at depths of 6 and 8 m, respectively. The mean wind shear energy was 9.8 × 10–4 m2 s–2, and the energy of the surface gravity wave break was 10.8 × 10–2 m2 s–2, and both served to enhance vertical mixing in the area. A permanent thermocline between the 70- and 150-m depths was present throughout the year. The isohaline distribution followed an isotherm pattern of variation, but at times, the formation of low-salinity eddies was verified on the bank slope. The 3D POM model reproduced the thermohaline structure accurately. Temperature and salinity profiles indicated the existence of vertical water displacements over the bank and along the direction of the North Brazil Current, which is the strongest western boundary current crossing the equatorial Atlantic. The kinematic structure observed in the simulations indicated vertical velocities of O (10–3 m.s–1) in the upstream region of the bank during austral winter and summer seasons. During the summer, the most important vertical velocities were localized below the lower limit of the euphotic zone; while during the austral winter, these velocities were within the euphotic zone, thereby favoring primary producers.

scholarly journals Impact of horizontal resolution on global ocean-sea-ice model simulations based on the experimental protocols of the Ocean Model Intercomparison Project phase 2 (OMIP-2)

2020 ◽  
Author(s):  
Eric P. Chassignet ◽  
Stephen G. Yeager ◽  
Baylor Fox-Kemper ◽  
Alexandra Bozec ◽  
Fred Castruccio ◽  
...  
Keyword(s):  
High Resolution ◽  
Sea Ice ◽  
Global Climate ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Global Ocean ◽  
Western Boundary ◽  
Low Resolution ◽  
Circumpolar Current ◽  
High Resolution Models

Abstract. This paper presents global comparisons of fundamental global climate variables from a suite of four pairs of matched low- and high-resolution ocean and sea-ice simulations that are obtained following the OMIP-2 protocol (Griffies et al., 2016) and integrated for one cycle (1958–2018) of the JRA55-do atmospheric state and runoff dataset (Tsujino et al., 2018). Our goal is to assess the robustness of climate-relevant improvements in ocean simulations (mean and variability) associated with moving from coarse (~ 1º) to eddy-resolving (~ 0.1º) horizontal resolutions. The models are diverse in their numerics and parameterizations, but each low-resolution and high-resolution pair of models is matched so as to isolate, to the extent possible, the effects of horizontal resolution. A variety of observational datasets are used to assess the fidelity of simulated temperature and salinity, sea surface height, kinetic energy, heat and volume transports, and sea ice distribution. This paper provides a crucial benchmark for future studies comparing and improving different schemes in any of the models used in this study or similar ones. The biases in the low-resolution simulations are familiar and their gross features – position, strength, and variability of western boundary currents, equatorial currents, and Antarctic Circumpolar Current – are significantly improved in the high-resolution models. However, despite the fact that the high-resolution models "resolve" most of these features, the improvements in temperature or salinity are inconsistent among the different model families and some regions show increased bias over their low-resolution counterparts. Greatly enhanced horizontal resolution does not deliver unambiguous bias improvement in all regions for all models.

On the variability of the DWBC transport between 26.5°N and 16°N in an eddy-rich ocean model and its implications for meridionally coherent changes.

2021 ◽  
Author(s):  
Tobias Schulzki ◽  
Klaus Getzlaff ◽  
Arne Biastoch
Keyword(s):  
North Atlantic ◽  
Time Distribution ◽  
Ocean Model ◽  
High Variability ◽  
Western Boundary ◽  
Barotropic Instability ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Transit Time Distribution ◽  
Southward Flow

<p>The southward flow of North Atlantic Deep Water makes up the major component of the AMOC's deepwater limb. In the subtropical North Atlantic, it's flow is concentrated along the continental slope, forming a coherent Deep Western Boundary Current (DWBC). Both, observations and models show a high variability of the flow in this region.<br>We use an eddy-rich ocean model to show that this variability is mainly caused by eddies and meanders that are generated by barotropic instability. They occur along the entire DWBC pathway and introduce several reciruculation gyres that result in a decorrelation of DWBC transport at 26.5°N and 16°N, despite the fact that a considerable mean transport of 20 Sv connects the two latitudes. Water in the DWBC at 26.5°N is partly returned northward. Because the amount of water returned depends on the DWBC transport itself, a stronger DWBC does not necessarily lead to an increased amount of water that reaches 16°N. <br>Along the pathway to 16°N, the transport signal is altered by a broad and temporally variable transit time distribution. Thus, advection in the DWBC cannot account for coherent AMOC changes on interannual timescales seen in the model.</p>

A NUMERICAL STUDY OF THE BRAZILIAN SHELF/SLOPE REGION SOUTH OF 13S USING THE OCEAN MODEL ROMS

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Janini Pereira ◽  
Mauro Cirano ◽  
Martinho Marta-almeida ◽  
Fabiola Negreiros Amorim
Keyword(s):  
Numerical Study ◽  
Current System ◽  
Mixed Layer Depth ◽  
Ocean Model ◽  
Western Boundary ◽  
Boundary Current ◽  
Data Set ◽  
Regional Ocean Model System ◽  
Brazil Current ◽  
Shelf Slope

The oceanic features in the eastern and southeastern brazilian shelf/slope south of 13S is investigated using ROMS (Regional Ocean Model System). The model integration was 9 years and it was forced with: i) 6-hourly synoptic atmospheric data from NCEP; ii) initial and boundary conditions from OCCAM (Ocean Climate Circulation Advanced Modelling) monthly mean climatology and iii) tidal forcing from TPXO 7.1 global data set. The model results were compared with observations, which consisted in thermodynamic MDL (Mixed Layer Depth) climatology, satellite data, measurements from tide gauges along the shelf and currents measurements values from literature. The simulated currents represented well the BC (Brazil Current)-IWBC (IntermediateWestern Boundary Current) System. The BC - IWBC system at 22S cross-shelf section, where the mean alongshelf velocity represents our simulation capability of reproducing the western boundary currents, showed poleward BC and a opposing IWBC. At this section, the BC velocity core is in 50 m with 0.41 m.s−1 and the IWBC core around 800 m with 0.15 m.s−1.

Sign in / Sign up

Export Citation Format

Share Document