scholarly journals Sensitivity study of the generation of mesoscale eddies in a numerical model of Hawaii islands

Ocean Science ◽  
2011 ◽  
Vol 7 (3) ◽  
pp. 277-291 ◽  
Author(s):  
M. Kersalé ◽  
A. M. Doglioli ◽  
A. A. Petrenko
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Cumulative Effect ◽  
Mesoscale Eddies ◽  
Sensitivity Study ◽  
Ocean Model ◽  
Ekman Pumping ◽  
Oceanic Circulation ◽  
Wind Stress Curl ◽  
Trade Winds

Abstract. The oceanic circulation around the Hawaiian archipelago is characterized by a complex circulation and the presence of mesoscale eddies west of the islands. These eddies typically develop and persist for weeks to several months in the area during persistent trade winds conditions. A series of numerical simulations on the Hawaiian region has been done in order to examine the relative importance of wind, inflow current and topographic forcing on the general circulation and the generation of eddies. Moreover, numerical cyclonic eddies are compared with the one observed during the cruise E-FLUX (Dickey et al., 2008). Our study demonstrates the need for all three forcings (wind, inflow current and topography) to reproduce the known oceanic circulation. In particular, the cumulative effect plays a key role on the generation of mesoscale eddies. The wind-stress-curl, via the Ekman pumping mechanism, has also been identified as an important mechanism upon the strength of the upwelling in the lee of the Big Island of Hawaii. In order to find the best setup of a regional ocean model, we compare more precisely numerical results obtained using two different wind databases: COADS and QuikSCAT. The main features of the ocean circulation in the area are well reproduced by our model forced by both COADS and QuickSCAT climatologies. Nevertheless, significant differences appear in the levels of kinetic energy and vorticity. The wind-forcing spatial resolution clearly affects the way in which the wind momentum feeds the mesoscale phenomena. The higher the resolution, the more realistic the ocean circulation. In particular, the simulation forced by QuikSCAT wind data reproduces well the observed energetic mesoscale structures and their hydrological characteristics and behaviors.

scholarly journals Sensitivity study of wind forcing in a numerical model of mesoscale eddies in the lee of Hawaii islands

2010 ◽  
Vol 7 (2) ◽  
pp. 477-500 ◽  
Author(s):  
M. Kersalé ◽  
A. M. Doglioli ◽  
A. A. Petrenko
Keyword(s):  
Kinetic Energy ◽  
Ocean Circulation ◽  
Mesoscale Eddies ◽  
Sensitivity Study ◽  
Ocean Model ◽  
Wind Forcing ◽  
Trade Wind ◽  
Oceanic Circulation ◽  
Mesoscale Structures ◽  
And Behavior

Abstract. The oceanic circulation around the Hawaiian archipelago is characterized by a complex circulation and the presence of mesoscale eddies west of the islands. These eddies typically develop and persist for weeks to several months in the area during persistent trade wind conditions. In order to find the best setup of a regional ocean model and to better understand the role of the wind forcing in the eddy formation, we compare numerical results obtained using two different wind stress databases: COADS and QuikSCAT. A detailed comparative analysis of wind forcing, modeled kinetic energy and eddy generation is proposed. Moreover, numerical cyclonic eddies are compared with the ones observed during the cruises E-FLUX (Dickey et al., 2008). The main features of the ocean circulation in the area are well reproduced by our model forced by both COADS and QuickSCAT climatologies. Nevertheless, significant differences appear in the levels of kinetic energy and vorticity. The wind-forcing spatial resolution clearly affects the way in which the wind momentum feeds the mesoscale phenomena, and, the higher the resolution, the more realistic the ocean circulation. In particular, the simulation forced by QuikSCAT wind data reproduces well the observed energetic mesoscale structures and their hydrological characteristics and behavior.

scholarly journals Upper-Bound General Circulation of the Ocean: A Theoretical Exposition

2021 ◽  
Vol 9 (10) ◽  
pp. 1090
Author(s):  
Hsien-Wang Ou
Keyword(s):  
Ocean Circulation ◽  
Upper Bound ◽  
First Principles ◽  
General Circulation ◽  
Large Scale ◽  
Companion Paper ◽  
Trade Winds ◽  
Equatorial Undercurrent ◽  
Macroscopic Motion ◽  
Dynamical Principle

This paper considers the general ocean circulation (GOC) within the thermodynamical closure of our climate theory, which aims to deduce the generic climate state from first principles. The preceding papers of this theory have reduced planetary fluids to warm/cold masses and determined their bulk properties, which provide prior constraints for the derivation of the upper-bound circulation when the potential vorticity (PV) is homogenized in moving masses. In a companion paper on the general atmosphere circulation (GAC), this upper bound is seen to reproduce the observed prevailing wind, therefore forsaking discordant explanations of the easterly trade winds and the polar jet stream. In this paper on the ocean, we again show that this upper bound may replicate broad features of the observed circulation, including a western-intensified subtropical gyre and a counter-rotating tropical gyre feeding the equatorial undercurrent. Since PV homogenization has short-circuited the wind curl, the Sverdrup dynamics does not need to be the sole progenitor of the western intensification, as commonly perceived. Together with GAC, we posit that PV homogenization provides a unifying dynamical principle of the large-scale planetary circulation, which may be interpreted as the maximum macroscopic motion extractable by microscopic stirring, within the confines of thermal differentiation.

Using the depth of the centre of gravity as an indicator on the state of the general ocean circulation

2021 ◽  
Author(s):  
Benjamin Schmiedel ◽  
Fabien Roquet
Keyword(s):  
Potential Energy ◽  
Ocean Circulation ◽  
General Circulation ◽  
Model Simulation ◽  
Ocean Model ◽  
The State ◽  
Relative Role ◽  
Centre Of Gravity ◽  
Gravity Centre ◽  
Global Mean

<p>An approach is here investigated that uses the depth of the centre of gravity as a central ocean property, thought to give a clear and practical indicator on the state of the general ocean circulation. The depth of the gravity centre can be directly linked to the volume-integral of potential energy, or of dynamic enthalpy when making the Boussinesq approximation, and therefore to the strength of the global mean stratification. Because the stratification is directly linked to the global overturning circulation, it is hypothesized that the depth of the centre of gravity can be used to assess the state of global circulation. In order to test this hypothesis, the depth of the centre of gravity is diagnosed in an ocean model simulation for an idealized square basin configuration with the NEMO model. The centre of gravity is compared to the value it would have if the ocean was perfectly well mixed, giving a state of maximum potential energy. We find in our idealized simulation that the centre of gravity is lowered by only 22 cm compared to the reference well-mixed state, reflecting the potential energy that would be required to destroy the ocean stratification. The smallness of that number highlights the inefficiency of the ocean engine. Furthermore, the dynamic balance setting the depth of the gravity centre is investigated, diagnosing separately the tendency terms on the equation of conservation of potential energy. A positive change (sinking) of the centre of gravity indicates an input of high density water into lower levels or low density water in upper levels, essentially enhancing the global mean stratification, while for a negative change (lifting) it is reversed. The goal is to compare the relative role of the wind stress, surface buoyancy forcing and internal mixing in setting the general circulation.</p>

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 A nested Atlantic-Mediterranean Sea general circulation model for operational forecasting

Ocean Science ◽  
2009 ◽  
Vol 5 (4) ◽  
pp. 461-473 ◽  
Author(s):  
P. Oddo ◽  
M. Adani ◽  
N. Pinardi ◽  
C. Fratianni ◽  
M. Tonani ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
General Circulation Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Lateral Boundary ◽  
The Mediterranean ◽  
The Impact

Abstract. A new numerical general circulation ocean model for the Mediterranean Sea has been implemented nested within an Atlantic general circulation model within the framework of the Marine Environment and Security for the European Area project (MERSEA, Desaubies, 2006). A 4-year twin experiment was carried out from January 2004 to December 2007 with two different models to evaluate the impact on the Mediterranean Sea circulation of open lateral boundary conditions in the Atlantic Ocean. One model considers a closed lateral boundary in a large Atlantic box and the other is nested in the same box in a global ocean circulation model. Impact was observed comparing the two simulations with independent observations: ARGO for temperature and salinity profiles and tide gauges and along-track satellite observations for the sea surface height. The improvement in the nested Atlantic-Mediterranean model with respect to the closed one is particularly evident in the salinity characteristics of the Modified Atlantic Water and in the Mediterranean sea level seasonal variability.

scholarly journals Stability of the Global Ocean Circulation: Basic Bifurcation Diagrams

2005 ◽  
Vol 35 (6) ◽  
pp. 933-948 ◽  
Author(s):  
Henk A. Dijkstra ◽  
Wilbert Weijer
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Multiple Equilibria ◽  
Stable Solution ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Freshwater Flux ◽  
Surface Salinity ◽  
Global Ocean Circulation

Abstract A study of the stability of the global ocean circulation is performed within a coarse-resolution general circulation model. Using techniques of numerical bifurcation theory, steady states of the global ocean circulation are explicitly calculated as parameters are varied. Under a freshwater flux forcing that is diagnosed from a reference circulation with Levitus surface salinity fields, the global ocean circulation has no multiple equilibria. It is shown how this unique-state regime transforms into a regime with multiple equilibria as the pattern of the freshwater flux is changed in the northern North Atlantic Ocean. In the multiple-equilibria regime, there are two branches of stable steady solutions: one with a strong northern overturning in the Atlantic and one with hardly any northern overturning. Along the unstable branch that connects both stable solution branches (here for the first time computed for a global ocean model), the strength of the southern sinking in the South Atlantic changes substantially. The existence of the multiple-equilibria regime critically depends on the spatial pattern of the freshwater flux field and explains the hysteresis behavior as found in many previous modeling studies.

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 Impacts of the Madden–Julian Oscillation on the Summer South China Sea Ocean Circulation and Temperature

2013 ◽  
Vol 26 (20) ◽  
pp. 8084-8096 ◽  
Author(s):  
Guihua Wang ◽  
Zheng Ling ◽  
Renguang Wu ◽  
Changlin Chen
Keyword(s):  
South China Sea ◽  
Ocean Circulation ◽  
South China ◽  
Ocean Model ◽  
Ocean Modeling ◽  
Madden Julian Oscillation ◽  
Regional Ocean Modeling System ◽  
Wind Stress Curl ◽  
China Sea ◽  
The Impact

Abstract The present study investigates the impact of the Madden–Julian oscillation (MJO) on the South China Sea (SCS) in summer with three types of models: a theoretical Sverdrup model, a 1.5-layer reduced gravity model, and a regional ocean model [Regional Ocean Modeling System (ROMS)]. Results show that the ocean circulation in the SCS has an intraseasonal oscillation responding to the MJO. During its westerly phase, the MJO produces positive (negative) wind stress curl over the northern (southern) SCS and thus induces an enhanced cyclonic (anticyclonic) circulation in the northern (southern) SCS. This not only cools sea surface temperature (SST) but also decreases (increases) subsurface temperature in the northern (southern) SCS. During its easterly phase, the MJO basically produces a reversed but weaker influence on SCS ocean circulation and temperature. Thus, the MJO can have an imprint on the summer climatology of SCS circulation and temperature. The authors' analysis further indicates that the MJO's dynamic effect associated with wind is generally more important than its thermodynamic effect in modulating the regional ocean circulation and temperature. The present study suggests that the MJO is important for summer ocean circulation and temperature in the SCS.

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 On the Patterns of Wind-Power Input to the Ocean Circulation

2011 ◽  
Vol 41 (12) ◽  
pp. 2328-2342 ◽  
Author(s):  
Fabien Roquet ◽  
Carl Wunsch ◽  
Gurvan Madec
Keyword(s):  
Wind Power ◽  
Ocean Circulation ◽  
General Circulation ◽  
Average Energy ◽  
Power Input ◽  
Ekman Pumping ◽  
Ekman Theory ◽  
Global Mean Sea Level ◽  
Circumpolar Current ◽  
Work Done

Abstract Pathways of wind-power input into the ocean general circulation are analyzed using Ekman theory. Direct rates of wind work can be calculated through the wind stress acting on the surface geostrophic flow. However, because that energy is transported laterally in the Ekman layer, the injection into the geostrophic interior is actually controlled by Ekman pumping, with a pattern determined by the wind curl rather than the wind itself. Regions of power injection into the geostrophic interior are thus generally shifted poleward compared to regions of direct wind-power input, most notably in the Southern Ocean, where on average energy enters the interior 10° south of the Antarctic Circumpolar Current core. An interpretation of the wind-power input to the interior is proposed, expressed as a downward flux of pressure work. This energy flux is a measure of the work done by the Ekman pumping against the surface elevation pressure, helping to maintain the observed anomaly of sea surface height relative to the global-mean sea level.

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