scholarly journals Circulation and heat budget in a regional climatological simulation of the Southwestern Tropical Atlantic.

2009 ◽  
Vol 37 (1-2) ◽  
Author(s):  
Marcus SILVA ◽  
Moacyr ARAÚJO ◽  
Jacques SERVAIN ◽  
Penven Pierrick
Keyword(s):  
Ocean Circulation ◽  
Heat Budget ◽  
Thermal Structure ◽  
Climatic Variability ◽  
Mixing Layer ◽  
Upper Ocean ◽  
Western Boundary ◽  
Tropical Atlantic ◽  
The South ◽  
Data Set

Surface and vertical thermal structures, heat budget in the surface mixing layer, and mass transports are explored in the south-western tropical Atlantic (5oS-25oS / 20oW-47oW). That region, where part of the South Equatorial Current (SEC) enters at its eastern border, is of prime interest by feeding many western boundary currents along the eastern Brazilian edge, and by contributing to the climatic variability over the Northeast Brazil. The Regional Ocean Model System (ROMS) is used here to simulate a seasonal cycle of the ocean circulation with an isotropic horizontal grid resolution of 1/12o and 40 terrain-following layers. Such a high-resolution regional model allows illustrating the complexity of meso-scales phenomena which occur in that region. Model results are compared with the very first annual series of observed thermal profiles available in the region thanks to the three PIRATA-SWE moorings recently deployed. Simulated thermal structure at the upper ocean layers agrees with in-situ data set. Seasonal evolutions of atmospheric and oceanic balances involving in the mixing layer heat budget are locally discussed. The magnitude of oceanic components (mainly the vertical diffusion and the horizontal advection) is about of the same order than of atmospheric forcing, and practically always opposes to it, with some local and seasonal timing differences. Simulated meridional transports across three zonal sections extending from continent to PIRATA sites provide new insight in the knowledge of the western boundary current system. Another section running along the PIRATA-SWE array indicates how the divergence of SEC is complex. This result encourages the need and future expansion of the observational PIRATA array system in that region. Keywords: South Western Tropical Atlantic, Upper Ocean layers, Ocean heat budget, PIRATA-SWE moorings, ROMS

scholarly journals Closing the Time-Varying Mass and Heat Budgets for Large Ocean Areas: The Tasman Box

2005 ◽  
Vol 18 (13) ◽  
pp. 2330-2343 ◽  
Author(s):  
Dean Roemmich ◽  
John Gilson ◽  
Josh Willis ◽  
Philip Sutton ◽  
Ken Ridgway
Keyword(s):  
Heat Flux ◽  
New Zealand ◽  
Heat Loss ◽  
Ocean Circulation ◽  
Heat Budget ◽  
Current System ◽  
Western Boundary Current ◽  
Upper Ocean ◽  
Western Boundary ◽  
Boundary Current

Abstract The role of oceanic advection in seasonal-to-interannual balances of mass and heat is studied using a 12-yr time series of quarterly eddy-resolving expendable bathythermograph (XBT) surveys around the perimeter of a region the authors call the Tasman Box in the southwestern Pacific. The region contains the South Pacific’s subtropical western boundary current system and associated strong mesoscale variability. Mean geostrophic transport in the warm upper ocean (temperature greater than 12°C) is about 3.8 Sv (1 Sv ≡ 106 m3 s−1) southward into the box across the Brisbane, Australia–Fiji northern edge. Net outflows are 3.3 Sv eastward across the Auckland, New Zealand–Fiji edge, and 2.7 Sv southward across Sydney, Australia–Wellington, New Zealand. Mean Ekman convergence of 2.2 Sv closes the mass budget. Net water mass conversions in the upper ocean consist of inflow of waters averaging about 26°C and 35.4 psu balanced by outflow at about 18°C and 35.7 psu, and reflect the net evaporation and heat loss in the formation of South Pacific Subtropical Mode Water. The mean heat balance shows good agreement between ocean heat flux convergence (42.3 W m−2), heat loss to the atmosphere from the NCEP–NCAR reanalysis (39.2 W m−2), and heat storage calculated from data in the box interior (1.3 W m−2). On interannual time scales, volume transport through the box ranges from about 1 to 9 Sv, with heat flux convergence ranging from about 20 to 60 W m−2. An interannual balance in the heat budget of the warm layer is achieved to within about 10 W m−2 (or 6 W m−2 for the upper 100 m alone). Maxima in the advective heat flux convergence occurred in 1993, 1997, and 1999–2000, and corresponded to maxima in air–sea heat loss. The evolution of surface-layer temperature in the region is the residual of nearly equal and opposing effects of ocean heat flux convergence and air–sea exchange. Hence, ocean circulation is a key element in the interannual heat budget of the air–sea climate system in the western boundary current region.

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.

The response of the thermal stratification of South Bay (Lake Huron) to climatic variability

1997 ◽  
Vol 54 (8) ◽  
pp. 1873-1882 ◽  
Author(s):  
J R King ◽  
B J Shuter ◽  
A P Zimmerman
Keyword(s):  
Thermal Structure ◽  
Climatic Variability ◽  
Warming Trend ◽  
Lake Huron ◽  
Thermal Gradients ◽  
Data Set ◽  
Mount Pinatubo ◽  
Recent Warming ◽  
Air Temperatures ◽  
Canonical Analyses

The 37-year record (1955-1992) of water temperature profiles and corresponding meteorology for South Bay (Lake Huron) provide an extensive empirical data set for the study of climate variability and corresponding alterations in lake thermal structure. Thermoclines became shallower over this period and epilimnetic temperatures increased. Canonical analyses correlated warm May-July air temperatures and high July-August solar radiation with warmer epilimnia, larger thermal gradients across the thermocline, and shallower thermoclines. Multivariate canonical scores indicate that these thermal responses have increased in parallel with the recent warming trend since the mid-1960s. Anomalous multivariate scores correspond to El Niño events, and an extreme low score corresponds to the Mount Pinatubo cooling effect of 1992.

scholarly journals Transport across 48°N in the Atlantic Ocean

2008 ◽  
Vol 38 (4) ◽  
pp. 733-752 ◽  
Author(s):  
Rick Lumpkin ◽  
Kevin G. Speer ◽  
K. Peter Koltermann
Keyword(s):  
Atlantic Ocean ◽  
Ocean Circulation ◽  
World Ocean ◽  
Inverse Model ◽  
Reference Level ◽  
Western Boundary ◽  
North Atlantic Current ◽  
Data Set ◽  
Freshwater Fluxes ◽  
World Ocean Circulation Experiment

Abstract Transports across 48°N in the Atlantic Ocean are estimated from five repeat World Ocean Circulation Experiment (WOCE) hydrographic lines collected in this region in 1993–2000, from time-varying air–sea heat and freshwater fluxes north of 48°N, and from a synthesis of these two data sources using inverse box model methods. Results from hydrography and air–sea fluxes treated separately are analogous to recently published transport variation studies and demonstrate the sensitivity of the results to either the choice of reference level and reference velocities for thermal wind calculations or the specific flux dataset chosen. In addition, flux-based calculations do not include the effects of subsurface mixing on overturning and transports of specific water masses. The inverse model approach was used to find unknown depth-independent velocities, interior diapycnal fluxes, and adjustments to air–sea fluxes subject to various constraints on the system. Various model choices were made to focus on annually averaged results, as opposed to instantaneous values during the occupation of the hydrographic lines. The results reflect the constraints and choices made in the construction of the model. The inverse model solutions show only marginal, not significantly different temporal changes in the net overturning cell strength and heat transport across 48°N. These small changes are similar to seasonally or annually averaged numerical model simulations of overturning. Significant variability is found for deep transports and air–sea flux quantities in density layers. Put another way, if one ignores the details of layer exchanges, the model can be constrained to produce the same net overturning for each repeat line; however, constraining individual layers to have the same transport for each line fails. Diapycnal fluxes are found to be important in the mean but are relatively constant from one repeat line to the next. Mean air–sea fluxes are modified slightly but are still essentially consistent with either the NCEP data or the National Oceanography Centre, Southampton (NOC) Comprehensive Ocean–Atmosphere Data Set (COADS) within error. Modest reductions in air–sea flux uncertainties would give these constraints a much greater impact. Direct transport estimates over broader regions than the western boundary North Atlantic Current are needed to help resolve circulation structure that is important for variability in net overturning.

Upper ocean circulation in the western tropical Atlantic in boreal fall 2000

2005 ◽  
Vol 52 (2) ◽  
pp. 221-240 ◽  
Author(s):  
Lothar Stramma ◽  
Monika Rhein ◽  
Peter Brandt ◽  
Marcus Dengler ◽  
Claus Böning ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Upper Ocean ◽  
Tropical Atlantic

scholarly journals Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

Ocean Science ◽  
2015 ◽  
Vol 11 (4) ◽  
pp. 629-641 ◽  
Author(s):  
G. S. Pilo ◽  
M. M. Mata ◽  
J. L. L. Azevedo
Keyword(s):  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Surface Characteristics ◽  
Propagation Distance ◽  
Western Boundary ◽  
Boundary Current ◽  
Mean Flow ◽  
Data Set ◽  
Brazil Current ◽  
Argentine Basin

Abstract. Oceanic eddies exist throughout the world oceans, but are more energetic when associated with western boundary currents (WBC) systems. In these regions, eddies play an important role in mixing and energy exchange. Therefore, it is important to quantify and qualify eddies associated with these systems. This is particularly true for the Southern Hemisphere WBC system where only few eddy censuses have been performed to date. In these systems, important aspects of the local eddy population are still unknown, like their spatial distribution and propagation patterns. Moreover, the understanding of these patterns helps to establish monitoring programs and to gain insight in how eddies would affect local mixing. Here, we use a global eddy data set to qualify eddies based on their surface characteristics in the Agulhas Current (AC), the Brazil Current (BC) and the East Australian Current (EAC) systems. The analyses reveal that eddy propagation within each system is highly forced by the local mean flow and bathymetry. Large values of eddy amplitude and temporal variability are associated with the BC and EAC retroflections, while small values occur in the centre of the Argentine Basin and in the Tasman Sea. In the AC system, eddy polarity dictates the propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC system eddies from both polarities cross south of Tasmania but only the anticyclonic ones reach the Great Australian Bight. For all three WBC systems, both cyclonic and anticyclonic eddies present a geographical segregation according to radius size and amplitude. Regions of high eddy kinetic energy are associated with the eddies' mean amplitudes, and not with their densities.

Subsurface warm biases in the tropical Atlantic and their attributions to the role of wind forcing and ocean vertical mixing

2022 ◽  
pp. 1-28
Keyword(s):  
Climate Models ◽  
Heat Budget ◽  
Thermal Structure ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Climate Simulation ◽  
Tropical Atlantic ◽  
Warm Bias ◽  
Budget Analysis ◽  
Almost All

Abstract Realistic ocean subsurface simulations of thermal structure and variation are critically important to the success in climate prediction and projection; currently, substantial systematic subsurface biases still exist in the state-of-the-art ocean and climate models. In this paper, subsurface biases in the tropical Atlantic (TA) are investigated by analyzing simulations from OMIP and conducting POP2-based ocean-only experiments. The subsurface biases are prominent in almost all OMIP simulations, characterized by two warm bias patches off the equator. By conducting two groups of POP2-based ocean-only experiments, two potential origins of the biases are explored, including uncertainties in wind forcing and vertical mixing parameterization, respectively. It is illustrated that the warm bias near 10° N can be slightly reduced by modulating prescribed wind field, and the warm biases over the entire basin are significantly reduced by reducing background diffusivity in the ocean interior in ways to match observations. By conducting heat budget analysis, it is found that the improved subsurface simulations are attributed to the enhanced cooling effect by constraining the vertical mixing diffusivity in terms of the observational estimate, implying that the overestimation of vertical mixing is primarily responsible for the subsurface warm biases in the TA. Since the climate simulation is very sensitive to the vertical mixing parameterization, more accurate representations of ocean vertical mixing are clearly needed in ocean and climate models.

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