scholarly journals Interaction of Additive Noise and Nonlinear Dynamics in the Double-Gyre Wind-Driven Ocean Circulation

2013 ◽  
Vol 43 (2) ◽  
pp. 366-381 ◽  
Author(s):  
Themistoklis P. Sapsis ◽  
Henk A. Dijkstra
Keyword(s):  
Nonlinear Dynamics ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Additive Noise ◽  
Noise Forcing ◽  
Quasigeostrophic Model ◽  
Wind Stress Field ◽  
Orthogonal Field ◽  
Correlation Properties ◽  
Double Gyre

Abstract In this paper the authors study the interactions of additive noise and nonlinear dynamics in a quasigeostrophic model of the double-gyre wind-driven ocean circulation. The recently developed framework of dynamically orthogonal field theory is used to determine the statistics of the flows that arise through successive bifurcations of the system as the ratio of forcing to friction is increased. This study focuses on the understanding of the role of the spatial and temporal coherence of the noise in the wind stress forcing. When the wind stress noise is temporally white, the statistics of the stochastic double-gyre flow does not depend on the spatial structure and amplitude of the noise. This implies that a spatially inhomogeneous noise forcing in the wind stress field only has an effect on the dynamics of the flow when the noise is temporally colored. The latter kind of stochastic forcing may cause more complex or more coherent dynamics depending on its spatial correlation properties.

scholarly journals Influence of El Niño Wind Stress Anomalies on South Brazil Bight Ocean Volume Transports

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Luiz Paulo de Freitas Assad ◽  
Carina Stefoni Böck ◽  
Rogerio Neder Candella ◽  
Luiz Landau
Keyword(s):  
Stress Field ◽  
Interannual Variability ◽  
Wind Stress ◽  
Large Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Circulation Model ◽  
Volume Transport ◽  
Wind Stress Field ◽  
Volume Transports

The knowledge of wind stress variability could represent an important contribution to understand the variability over upper layer ocean volume transports. The South Brazilian Bight (SBB) circulation had been studied by numerous researchers who predominantly attempted to estimate its meridional volume transport. The main objective and contribution of this study is to identify and quantify possible interannual variability in the ocean volume transport in the SBB induced by the sea surface wind stress field. A low resolution ocean global circulation model was implemented to investigate the volume transport variability. The results obtained indicate the occurrence of interannual variability in meridional ocean volume transports along three different zonal sections. These results also indicate the influence of a wind driven large-scale atmospheric process that alters locally the SBB and near-offshore region wind stress field and consequently causes interannual variability in the upper layer ocean volume transports. A strengthening of the southward flow in 25°S and 30°S was observed. The deep layer ocean volume transport in the three monitored sections indicates a potential dominance of other remote ocean processes. A small time lag between the integrated meridional volume transports changes in each monitored zonal section was observed.

scholarly journals The influence of the ocean circulation state on ocean carbon storage and CO<sub>2</sub> drawdown potential in an Earth system model

2017 ◽  
Author(s):  
Malin Ödalen ◽  
Jonas Nycander ◽  
Kevin I. C. Oliver ◽  
Laurent Brodeau ◽  
Andy Ridgwell
Keyword(s):  
Carbon Storage ◽  
Wind Stress ◽  
Ocean Circulation ◽  
System Model ◽  
Biological Pump ◽  
Earth System ◽  
Heat Diffusivity ◽  
Initial States ◽  
Ocean Carbon ◽  
Atmospheric Heat

Abstract. During the four most recent glacial cycles, atmospheric CO2 during glacial maxima has been lowered by about 90–100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is however still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to constrain the range in ocean carbon storage for an ensemble of ocean circulation equilibrium states. We do a set of simulations where we run the model to pre-industrial equilibrium, but where we achieve different ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air-sea CO2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO2 disequilibrium component. We also relate these contributions to differences in strength of ocean overturning circulation. In cases with weaker circulation, we see that the ocean's capacity for carbon storage is larger. Depending on which ocean forcing parameter that is tuned, the origin of the change in carbon storage is different. When wind stress or ocean vertical diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean horizontal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Finally, we do a drawdown experiment, where we investigate the capacity for increased carbon storage by maximising the efficiency of the biological pump in our ensemble members. We conclude that different initial states for an ocean model result in different capacities for ocean carbon storage, due to differences in the ocean circulation state. This could explain why it is difficult to achieve comparable responses of the ocean carbon pumps in model intercomparison studies, where the initial states vary between models. The drawdown experiment highlights the importance of the strength of the biological pump in the control state for model studies of increased biological efficiency.

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 Two Different Aperiodic Phases of Wind-Driven Ocean Circulation in a Double-Gyre, Two-Layer Shallow-Water Model

2006 ◽  
Vol 36 (7) ◽  
pp. 1265-1286 ◽  
Author(s):  
Tomonori Matsuura ◽  
Mitsutaka Fujita
Keyword(s):  
Power Spectrum ◽  
Shallow Water ◽  
Metastable State ◽  
Ocean Circulation ◽  
Lower Layer ◽  
Water Model ◽  
Barotropic Instability ◽  
Shallow Water Model ◽  
Gyre Circulation ◽  
Double Gyre

Abstract A two-layer shallow-water model is used to investigate the transition of wind-driven double-gyre circulation from laminar flow to turbulence as the Reynolds number (Re) is systematically increased. Two distinctly different phases of turbulent double-gyre patterns and energy trajectories are exhibited before and after at Re = 95: deterministic and fully developed turbulent circulations. In the former phase, the inertial subgyres vary between an asymmetric solution and an antisymmetric solution and the double-gyre circulations reach the aperiodic solution mainly due to their barotropic instability. An integrated kinetic energy in the lower layer is slight and the generated mesoscale eddies are confined in the upper layer. The power spectrum of energies integrated over the whole domain at Re = 70 has peaks at the interannual periods (4–7 yr) and the interdecadal period (10–20 yr). The loops of the attractors take on one cycle at those periods and display the blue-sky catastrophe. At Re = 95, the double-gyre circulation reaches a metastable state and the attracters obtained from the three energies form a topological manifold. In the latter, as Re increases, the double-gyre varies from a metastable state to a chaotic state because of the barotropic instability of the eastward jet and the baroclinic instability of recirculation retrograde flow, and the eastward jet meanders significantly with interdecadal variability. The generated eddies cascade to the red side of the power spectrum as expected in the geostrophic turbulence. The main results in the simulation may indicate essential mechanisms for the appearance of multiple states of the Kuroshio and for low-frequency variations in the midlatitude ocean.

scholarly journals Chaotic Behaviors in the Response of a Quasigeostrophic Oceanic Double Gyre to Seasonal External Forcing

2010 ◽  
Vol 40 (7) ◽  
pp. 1458-1472 ◽  
Author(s):  
Shinya Shimokawa ◽  
Tomonori Matsuura
Keyword(s):  
Nonlinear Oscillations ◽  
Variable Parameter ◽  
External Forcing ◽  
Strong Current ◽  
Decadal Variations ◽  
Current Region ◽  
Quasigeostrophic Model ◽  
Gyre System ◽  
Double Gyre

Abstract In an oceanic double-gyre system, nonlinear oscillations of the ocean under seasonally changing external forcing are investigated using a 1.5-layer quasigeostrophic model and a simple model related to energy balance of the oceanic double gyre. In the experiments, the variable parameter is the amplitude of external seasonal forcing and the Reynolds number is fixed as 39, at which periodic shedding of inertial subgyres occurs. The authors found that entrainment (at 2 times the period of the forcing) and intermittency (on–off type), phenomena that are often seen in nonlinear systems, emerge with increasing amplitude of the forcing. They seem to be related to the generation mechanism and characteristics of long-term (from interannual to decadal) variations in the strong current region of subtropical gyres such as the Kuroshio and its extension region.

scholarly journals A wind-driven nonseasonal barotropic fluctuation of the Canadian inland seas

Ocean Science ◽  
2015 ◽  
Vol 11 (1) ◽  
pp. 175-185 ◽  
Author(s):  
C. G. Piecuch ◽  
R. M. Ponte
Keyword(s):  
Wind Stress ◽  
Ocean Circulation ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Tide Gauge ◽  
Bottom Topography ◽  
Dominant Mode ◽  
Tide Gauge Record ◽  
The North ◽  
The North Atlantic Oscillation

Abstract. A wind-driven, spatially coherent mode of nonseasonal, depth-independent variability in the Canadian inland seas (i.e., the collective of Hudson Bay, James Bay, and Foxe Basin) is identified based on Gravity Recovery and Climate Experiment (GRACE) retrievals, a tide-gauge record, and a barotropic model over 2003–2013. This dominant mode of nonseasonal variability is correlated with the North Atlantic Oscillation and is associated with net flows into and out of the Canadian inland seas; the anomalous inflows and outflows, which are reflected in mean sea level and bottom pressure changes, are driven by wind stress anomalies over Hudson Strait, probably related to wind setup, as well as over the northern North Atlantic Ocean, possibly mediated by various wave mechanisms. The mode is also associated with mass redistribution within the Canadian inland seas, reflecting linear response to local wind stress variations under the combined influences of rotation, gravity, and variable bottom topography. Results exemplify the usefulness of GRACE for studying regional ocean circulation and climate.

An Adjoint Analysis of the Meridional Overturning Circulation in a Hybrid Coupled Model

2006 ◽  
Vol 19 (15) ◽  
pp. 3751-3767 ◽  
Author(s):  
Véronique Bugnion ◽  
Chris Hill ◽  
Peter H. Stone
Keyword(s):  
Boundary Conditions ◽  
Wind Stress ◽  
Ocean Circulation ◽  
General Circulation ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Model Parameters ◽  
Overturning Circulation ◽  
Near Surface ◽  
Meridional Overturning

Abstract Multicentury sensitivities in a realistic geometry global ocean general circulation model are analyzed using an adjoint technique. This paper takes advantage of the adjoint model’s ability to generate maps of the sensitivity of a diagnostic (i.e., the meridional overturning’s strength) to all model parameters. This property of adjoints is used to review several theories, which have been elaborated to explain the strength of the North Atlantic’s meridional overturning. This paper demonstrates the profound impact of boundary conditions in permitting or suppressing mechanisms within a realistic model of the contemporary ocean circulation. For example, the so-called Drake Passage Effect in which wind stress in the Southern Ocean acts as the main driver of the overturning’s strength, is shown to be an artifact of boundary conditions that restore the ocean’s surface temperature and salinity toward prescribed climatologies. Advective transports from the Indian and Pacific basins play an important role in setting the strength of the overturning circulation under “mixed” boundary conditions, in which a flux of freshwater is specified at the ocean’s surface. The most “realistic” regime couples an atmospheric energy and moisture balance model to the ocean. In this configuration, inspection of the global maps of sensitivity to wind stress and diapycnal mixing suggests a significant role for near-surface Ekman processes in the Tropics. Buoyancy also plays an important role in setting the overturning’s strength, through direct thermal forcing near the sites of convection, or through the advection of salinity anomalies in the Atlantic basin.

scholarly journals Annual Sea Level Changes on the North American Northeast Coast: Influence of Local Winds and Barotropic Motions

2016 ◽  
Vol 29 (13) ◽  
pp. 4801-4816 ◽  
Author(s):  
Christopher G. Piecuch ◽  
Sönke Dangendorf ◽  
Rui M. Ponte ◽  
Marta Marcos
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Tide Gauge ◽  
Sea Level Changes ◽  
Tide Gauge Records ◽  
Barotropic Model ◽  
The North ◽  
Ocean Reanalyses ◽  
Coastal Sea

Abstract Understanding the relationship between coastal sea level and the variable ocean circulation is crucial for interpreting tide gauge records and projecting sea level rise. In this study, annual sea level records (adjusted for the inverted barometer effect) from tide gauges along the North American northeast coast over 1980–2010 are compared to a set of data-assimilating ocean reanalysis products as well as a global barotropic model solution forced with wind stress and barometric pressure. Correspondence between models and data depends strongly on model and location. At sites north of Cape Hatteras, the barotropic model shows as much (if not more) skill than ocean reanalyses, explaining about 50% of the variance in the adjusted annual tide gauge sea level records. Additional numerical experiments show that annual sea level changes along this coast from the barotropic model are driven by local wind stress over the continental shelf and slope. This result is interpreted in the light of a simple dynamic framework, wherein bottom friction balances surface wind stress in the alongshore direction and geostrophy holds in the across-shore direction. Results highlight the importance of barotropic dynamics on coastal sea level changes on interannual and decadal time scales; they also have implications for diagnosing the uncertainties in current ocean reanalyses, using tide gauge records to infer past changes in ocean circulation, and identifying the physical mechanisms responsible for projected future regional sea level rise.

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