Multidecadal simulation of the tropical and subtropical South Atlantic Ocean with a high resolution ocean model forced by ERA-5 reanalysis data

2020 ◽  
Author(s):  
Martin Schmidt ◽  
Hadi Bordbar ◽  
Fernanda Nascimento ◽  
Claudia Frauen
Keyword(s):  
High Resolution ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Reanalysis Data ◽  
Ocean Model ◽  
Ecosystem Dynamics ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Data Set ◽  
Upwelling Intensity

<p>High resolution regional ocean circulation models are needed to investigate regional ecosystem dynamics. However, these models may suffer from biases due to shortcomings in reanalysis datasets like NCEP or ERA-Interin, that have traditionally been used as atmospheric forcing. More realistic results can be achieved by replacing the reanalysed wind with scatterometer based winds. However, inconsistencies between different scatterometers like ASCAT and QuikSCAT introduce new uncertainty, which prevents a discussion of long-term trends in these models. The ERA-5 reanalysis offers a new consistent data set to force highly resolving regional ocean models. Based on such a simulation we analyse trends and anomalies in poleward currents in the Eastern Boundary Current off Southern Africa and Northern Benguela upwelling intensity due to changing wind stress and wind stress curl. Model results are validated with remote sensing as well as shipborne and mooring data. Further, variability of oxygen conditions in the Northern Benguela and the Angola Gyre oxygen minimum zone is discussed. </p>

scholarly journals Central Mediterranean Sea forecast: effects of high-resolution atmospheric forcings

2006 ◽  
Vol 3 (3) ◽  
pp. 637-669 ◽  
Author(s):  
S. Natale ◽  
R. Sorgente ◽  
S. Gaberšek ◽  
A. Ribotti ◽  
A. Olita
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Surface Current ◽  
Ocean Model ◽  
Central Mediterranean ◽  
Resolution Model ◽  
Atmospheric Forcings ◽  
Very High

Abstract. Ocean forecasts over the Central Mediterranean, produced by a near real time regional scale system, have been evaluated in order to assess their predictability. The ocean circulation model has been forced at the surface by a medium, high or very high resolution atmospheric forcing. The simulated ocean parameters have been compared with satellite data and they were found to be generally in good agreement. High and very high resolution atmospheric forcings have been able to form noticeable, although short-lived, surface current structures, due to their ability to detect transient atmospheric disturbances. The existence of the current structures has not been directly assessed due to lack of measurements. The ocean model in the slave mode was not able to develop dynamics different from the driving coarse resolution model which provides the boundary conditions.

scholarly journals Assymmetric eddy populations in adjacent basins – a high resolution numerical study of the Tyrrhenian and Ligurian Seas

2012 ◽  
Vol 9 (6) ◽  
pp. 3521-3566 ◽  
Author(s):  
R. M. A. Caldeira ◽  
X. Couvelard ◽  
E. Casella ◽  
A. Vetrano
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Mesoscale Eddy ◽  
Leeward Side ◽  
Boundary Current ◽  
High Concentration ◽  
Eddy Activity ◽  
Tyrrhenian Basin

Abstract. A high-resolution ocean circulation modelling system forced with a high-resolution numerical wind product was used to study the mesoscale and sub-mesoscale eddy population of the North-Western Mediterranean Sea, contrasting eddy-activity between the Tyrrhenian and Ligurian sub-basins. Numerical solutions reproduced some of the known regional dynamics, namely the occurrence and oceanic implications of Mistral events, the convective cell leeward of the Gulf of Lion, as well as the Balearic frontal system. Calculated transport across the Corsica Channel followed a similar trend, when compared to the transport computed from a moored current meter. The analysis of the results showed that surface eddy activity is mostly confined to the boundary-currents, whereas in the deeper layers most eddies are concentrated on the central-deeper part of the basins. The Liguro-Provençal basin shows a much higher concentration of intermediate and deep-water eddies, when compared to the Tyrrhenian basin. Sub-mesoscale surface eddies tend to merge and migrate vertically onto intermediate waters. Intense eddy activity in the boundary-current surrounding the Liguro-Provençal Gyre, concentrate high-productivity, manifested by higher concentrations of mean sea surface chlorophyll, in the central part of the gyre, defined herein as the Ligurian Productive Pool (LPP). On average, the Tyrrhenian was mostly oligotrophic except for a small productive vortice in the south-eastern (leeward) side of Corsica. The transport in the Tyrrhenian Gyre, and across the basin is one order of magnitude higher than the transport calculated for the Liguro-Provençal basin. A high concentration of eddies in the passage between the Balearic Archipelago and Sardinia suggests retention and longer residence times of nutrient rich water in the "Ligurian pool", compared to a "fast draining" Tyrrhenian basin. Previous studies support the cyclonic gyre circulation generated in the Liguro-Provençal basin but more studies are needed to address the surface and deep mesoscale activity of the Tyrrhenian basin.

scholarly journals THE BIFURCATION OF THE WESTERN BOUNDARY CURRENT SYSTEM OF THE SOUTH ATLANTIC OCEAN

2014 ◽  
Vol 32 (2) ◽  
pp. 241 ◽  
Author(s):  
Janini Pereira ◽  
Mariela Gabioux ◽  
Martinho Marta Almeida ◽  
Mauro Cirano ◽  
Afonso M. Paiva ◽  
...  
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Ocean Circulation ◽  
South Atlantic ◽  
Western Boundary Current ◽  
South Atlantic Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The South

ABSTRACT. The results of two high-resolution ocean global circulation models – OGCMs (Hybrid Coordinate Ocean Model – HYCOM and Ocean Circulation andClimate Advanced Modeling Project – OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volumetransports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonalflows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water,bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S.For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shearat mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system havepreviously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presentedin the literature regarding flow bifurcations at the Brazilian coast.Keywords: Southwestern Atlantic circulation, water mass, OCCAM, HYCOM. RESUMO. Resultados de dois modelos globais de alta resolução (HYCOM e OCCAM) são analisados focando o sistema de Corrente de Contorno Oeste do Oceano Atlântico Sul. Os transportes de volume são calculados para diferentes níveis isopicnais que representam as principais massas de água da região. É apresentada a avaliação da latitude de bifurcação do fluxo zonal que atinge a costa, permitindo a formação dos fluxos da Corrente de Contorno Oeste para o sul e para o norte emdiferentes níveis de profundidades (ou isopicnal). Para a Água Tropical, a bifurcação da Corrente Sul Equatorial ocorre entre 13◦-15◦S, originando a Corrente do Brasil, e para a Água Central do Atlântico Sul ocorre em 22◦S. A bifurcação daÁgua Intermediária Antártica ocorre próximo de 28◦-30◦S, dando um aumento na instabilidade baroclínica da Corrente de Contorno Oeste em baixas latitudes e com um forte cisalhamento vertical em profundidades intermediárias. Ambos os modelos apresentamresultados similares e consistentes com estudos observacionais prévios. Considerando que as observações do sistema de Corrente de Contorno Oeste do Atlântico Sul são escassas, essas duas simulações independentes com modelos globais de alta resolução adicionam confiança aos valores apresentados na literatura, relacionadosaos fluxos das bifurcações na costa do Brasil.Palavras-chave: circulação do Atlântico Sudoeste, massas de água, OCCAM, HYCOM.

scholarly journals Response of North Atlantic Ocean Circulation to Atmospheric Weather Regimes

2014 ◽  
Vol 44 (1) ◽  
pp. 179-201 ◽  
Author(s):  
Nicolas Barrier ◽  
Christophe Cassou ◽  
Julie Deshayes ◽  
Anne-Marie Treguier
Keyword(s):  
Atlantic Ocean ◽  
Wind Stress ◽  
Ocean Circulation ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Wind Stress Curl ◽  
Overturning Circulation ◽  
Weather Regimes

Abstract A new framework is proposed for investigating the atmospheric forcing of North Atlantic Ocean circulation. Instead of using classical modes of variability, such as the North Atlantic Oscillation (NAO) or the east Atlantic pattern, the weather regimes paradigm was used. Using this framework helped avoid problems associated with the assumptions of orthogonality and symmetry that are particular to modal analysis and known to be unsuitable for the NAO. Using ocean-only historical and sensitivity experiments, the impacts of the four winter weather regimes on horizontal and overturning circulations were investigated. The results suggest that the Atlantic Ridge (AR), negative NAO (NAO−), and positive NAO (NAO+) regimes induce a fast (monthly-to-interannual time scales) adjustment of the gyres via topographic Sverdrup dynamics and of the meridional overturning circulation via anomalous Ekman transport. The wind anomalies associated with the Scandinavian blocking regime (SBL) are ineffective in driving a fast wind-driven oceanic adjustment. The response of both gyre and overturning circulations to persistent regime conditions was also estimated. AR causes a strong, wind-driven reduction in the strengths of the subtropical and subpolar gyres, while NAO+ causes a strengthening of the subtropical gyre via wind stress curl anomalies and of the subpolar gyre via heat flux anomalies. NAO− induces a southward shift of the gyres through the southward displacement of the wind stress curl. The SBL is found to impact the subpolar gyre only via anomalous heat fluxes. The overturning circulation is shown to spin up following persistent SBL and NAO+ and to spin down following persistent AR and NAO− conditions. These responses are driven by changes in deep water formation in the Labrador Sea.

scholarly journals The Benguela Upwelling System: Quantifying the Sensitivity to Resolution and Coastal Wind Representation in a Global Climate Model*

2015 ◽  
Vol 28 (23) ◽  
pp. 9409-9432 ◽  
Author(s):  
R. Justin Small ◽  
Enrique Curchitser ◽  
Katherine Hedstrom ◽  
Brian Kauffman ◽  
William G. Large
Keyword(s):  
Wind Stress ◽  
Climate Model ◽  
Coastal Upwelling ◽  
Ocean Model ◽  
Wind Stress Curl ◽  
Upwelling System ◽  
Wind Structure ◽  
Eastern Boundary ◽  
Benguela Upwelling ◽  
Atmosphere Model

Abstract Of all the major coastal upwelling systems in the world’s oceans, the Benguela, located off southwest Africa, is the one that climate models find hardest to simulate well. This paper investigates the sensitivity of upwelling processes, and of sea surface temperature (SST), in this region to resolution of the climate model and to the offshore wind structure. The Community Climate System Model (version 4) is used here, together with the Regional Ocean Modeling System. The main result is that a realistic wind stress curl at the eastern boundary, and a high-resolution ocean model, are required to well simulate the Benguela upwelling system. When the wind stress curl is too broad (as with a 1° atmosphere model or coarser), a Sverdrup balance prevails at the eastern boundary, implying southward ocean transport extending as far as 30°S and warm advection. Higher atmosphere resolution, up to 0.5°, does bring the atmospheric jet closer to the coast, but there can be too strong a wind stress curl. The most realistic representation of the upwelling system is found by adjusting the 0.5° atmosphere model wind structure near the coast toward observations, while using an eddy-resolving ocean model. A similar adjustment applied to a 1° ocean model did not show such improvement. Finally, the remote equatorial Atlantic response to restoring SST in a broad region offshore of Benguela is substantial; however, there is not a large response to correcting SST in the narrow coastal upwelling zone alone.

Positive Regional Sea Level Anomalies in Southern Brazil Due to Changes in Austral Atmospheric Circulation

2021 ◽  
Author(s):  
Venisse Schossler ◽  
Francisco Aquino ◽  
Jefferson Simões ◽  
Pedro Reis ◽  
Denilson Viana
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Altimeter Data ◽  
Western Boundary ◽  
Positive Trend ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Sea Level Anomalies ◽  
Regional Sea Level

Abstract Pressure gradients and winds play an important role in Southern Hemisphere (SH) sea levels, which are currently associated with the positive trend of the Southern Annular Mode (SAM). This study investigated regional sea level anomalies (SLAs) in the southern coast Brazil using altimeter data (1993–2019), post-processed by the X-TRACK (CTOH/LEGOS). We observed a negative SLA from 1993 to 2009 and a positive SLA from 2010 to 2019, with upward trends throughout the evaluation period. We analyzed wind stress curl, pressure, and wind fields at sea level (FNMOC and ERA 5, respectively) in addition to sea surface temperature and height anomalies (SSTA/SSHA-OISST) in the South Atlantic Ocean (SAO) for 1993–2009 and 2010–2019. In relation to the first period, the second shows the enhancement in Hadley and Walker cells and trade winds, in addition to greater SSTA and SSHA in SAO. The SAO subtropical gyre and zonal winds at 45°S contribute to the intensification of the western boundary current. A greater pressure gradient between the SAO surface and the southeast of South America is noteworthy. Regionally, the positive SAM brings an increase in sea level to the study area, caused by greater wind stress and variability in heat flows.

scholarly journals Changes in Ocean Heat Content Caused by Wave-Induced Mixing in a High-Resolution Ocean Model

2018 ◽  
Vol 48 (5) ◽  
pp. 1139-1150 ◽  
Author(s):  
Lachlan Stoney ◽  
Kevin J. E. Walsh ◽  
Steven Thomas ◽  
Paul Spence ◽  
Alexander V. Babanin
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Heat Content ◽  
Circulation Model ◽  
Additional Term ◽  
Ocean Model ◽  
Ocean Heat Content ◽  
Sea Surface ◽  
Wave Heights ◽  
Wave Induced

Abstract A parameterization of turbulent mixing from unbroken surface waves is included in a 16-yr simulation within a high-resolution ocean circulation model (MOM5). This “surface wave mixing” (SWM) derives from the wave orbital motion and is parameterized as an additional term in a k-epsilon model. We show that SWM leads to significant changes in sea surface temperatures but smaller changes in ocean heat content, and show the extent to which these changes can reduce pre-existing model biases with respect to observed data. Specifically, SWM leads to a widespread improvement in sea surface temperature in both hemispheres in summer and winter, while for ocean heat content the improvements are less clear. In addition, we show that introducing SWM can lead to an accumulation of wave-induced ocean heat content between years. While it has been well established that secular positive trends exist in global wave heights, we find that such trends are relatively unimportant in driving the accumulation of wave-induced ocean heat content. Rather, in response to the new source of mixing, the simulated ocean climate evolves toward a new equilibrium with greater total ocean heat content.

A three-dimensional model of the wind-driven ocean circulation

1968 ◽  
Vol 34 (4) ◽  
pp. 721-734 ◽  
Author(s):  
J. A. Johnson
Keyword(s):  
Ocean Circulation ◽  
Three Dimensional ◽  
Ekman Layer ◽  
Return Flow ◽  
Western Boundary ◽  
Dimensional Model ◽  
Boundary Current ◽  
Three Dimensional Model ◽  
Wind Stress Curl ◽  
Interior Flow

A linear three-dimensional model of the wind-driven ocean circulation is treated by boundary-layer methods. The interior flow, below the Ekman layer, differs from the classical gyres of Munk (1950). There is a north-eastwards transport of fluid from the western boundary current of the southern gyre across the latitude of zero wind stress curl into the northern gyre. A return flow in the Ekman layer preserves continuity.

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 Evaluation of CMIP3 and CMIP5 Wind Stress Climatology Using Satellite Measurements and Atmospheric Reanalysis Products

2013 ◽  
Vol 26 (16) ◽  
pp. 5810-5826 ◽  
Author(s):  
Tong Lee ◽  
Duane E. Waliser ◽  
Jui-Lin F. Li ◽  
Felix W. Landerer ◽  
Michelle M. Gierach
Keyword(s):  
Climate Variability ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Zonal Wind ◽  
Global Ocean ◽  
Equatorial Pacific Ocean ◽  
Equatorial Atlantic ◽  
Wind Stress Curl ◽  
Meridional Heat Transport ◽  
Easterly Wind

Abstract Wind stress measurements from the Quick Scatterometer (QuikSCAT) satellite and two atmospheric reanalysis products are used to evaluate the annual mean and seasonal cycle of wind stress simulated by phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The ensemble CMIP3 and CMIP5 wind stresses are very similar to each other. Generally speaking, there is no significant improvement of CMIP5 over CMIP3. The CMIP ensemble–average zonal wind stress has eastward biases at midlatitude westerly wind regions (30°–50°N and 30°–50°S, with CMIP being too strong by as much as 55%), westward biases in subtropical–tropical easterly wind regions (15°–25°N and 15°–25°S), and westward biases at high-latitude regions (poleward of 55°S and 55°N). These biases correspond to too strong anticyclonic (cyclonic) wind stress curl over the subtropical (subpolar) ocean gyres, which would strengthen these gyres and influence oceanic meridional heat transport. In the equatorial zone, significant biases of CMIP wind exist in individual basins. In the equatorial Atlantic and Indian Oceans, CMIP ensemble zonal wind stresses are too weak and result in too small of an east–west gradient of sea level. In the equatorial Pacific Ocean, CMIP zonal wind stresses are too weak in the central and too strong in the western Pacific. These biases have important implications for the simulation of various modes of climate variability originating in the tropics. The CMIP as a whole overestimate the magnitude of seasonal variability by almost 50% when averaged over the entire global ocean. The biased wind stress climatologies in CMIP not only have implications for the simulated ocean circulation and climate variability but other air–sea fluxes as well.

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