Numerical Investigation of the Middle Atlantic Bight Shelfbreak Frontal Circulation Using a High-Resolution Ocean Hindcast Model

Abstract A nested high-resolution ocean model is used to hindcast the Middle Atlantic Bight (MAB) shelfbreak circulation from December 2003 to June 2008. The model is driven by tidal harmonics, realistic atmospheric forcing, and dynamically consistent initial and open boundary conditions obtained from a large-scale circulation model. Simulated shelfbreak sea levels and tracer fields compare favorably with satellite observations and available in situ hydrographic climatology, demonstrating the utility of this nested ocean model for resolving the MAB shelfbreak circulation. The resulting time and space continuous hindcast solutions between January 2004 and December 2007 are used to describe the mean structures and temporal variations of the shelfbreak front and jet, the bottom boundary layer detachment, and the migration of the shelfbreak front. It is found that the shelfbreak jet and boundary convergence reach their maximum intensities in the spring, at which time the foot of the front also migrates to its farthest offshore position. Vorticity analyses reveal that the magnitude ratio of the mean relative vorticity between the seaward and the shoreward portions of the shelfbreak front is about 2:1. The shelfbreak ageostrophic circulation is largely controlled by the viscosity in the boundary layers and by the nonlinear advection in the flow interior. Simulated three-dimensional velocity and tracer fields are used to estimate the transport and heat and salt fluxes across the 200-m isobath. Within the model domain, the total cross-shelf water transport, the total eddy heat flux, and the total eddy salt flux are 0.035 ± 0.26 Sv (1 Sv ≡ 106 m3 s−1), 1.0 × 103 ± 4 × 104 W m−2, and 6.7 × 10−5 ± 7.0 × 10−4 kg m−2 s−1. The empirical orthogonal function (EOF) analysis on the 4-yr shelfbreak circulation hindcast solutions identifies two dominant modes. The first EOF mode accounts for 61% variance, confirming that the shelfbreak jet is a persistent year-round circulation feature. The second mode accounts for 13% variance, representing the baroclinic eddy passages across the shelf break.

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A high resolution hydrodynamic 3-D model simulation of the malta shelf area

Annales Geophysicae ◽

10.5194/angeo-21-323-2003 ◽

2003 ◽

Vol 21 (1) ◽

pp. 323-344 ◽

Cited By ~ 6

Author(s):

A. F. Drago ◽

R. Sorgente ◽

A. Ribotti

Keyword(s):

High Resolution ◽

Seasonal Variability ◽

General Circulation ◽

Large Scale ◽

Current Knowledge ◽

Model Simulation ◽

Circulation Model ◽

Surface Flow ◽

Open Boundary ◽

Shelf Area

Abstract. The seasonal variability of the water masses and transport in the Malta Channel and proximity of the Maltese Islands have been simulated by a high resolution (1.6 km horizontal grid on average, 15 vertical sigma layers) eddy resolving primitive equation shelf model (ROSARIO-I). The numerical simulation was run with climatological forcing and includes thermohaline dynamics with a turbulence scheme for the vertical mixing coefficients on the basis of the Princeton Ocean Model (POM). The model has been coupled by one-way nesting along three lateral boundaries (east, south and west) to an intermediate coarser resolution model (5 km) implemented over the Sicilian Channel area. The fields at the open boundaries and the atmospheric forcing at the air-sea interface were applied on a repeating "perpetual" year climatological cycle. The ability of the model to reproduce a realistic circulation of the Sicilian-Maltese shelf area has been demonstrated. The skill of the nesting procedure was tested by model-modelc omparisons showing that the major features of the coarse model flow field can be reproduced by the fine model with additional eddy space scale components. The numerical results included upwelling, mainly in summer and early autumn, along the southern coasts of Sicily and Malta; a strong eastward shelf surface flow along shore to Sicily, forming part of the Atlantic Ionian Stream, with a presence throughout the year and with significant seasonal modulation, and a westward winter intensified flow of LIW centered at a depth of around 280 m under the shelf break to the south of Malta. The seasonal variability in the thermohaline structure of the domain and the associated large-scale flow structures can be related to the current knowledge on the observed hydrography of the area. The level of mesoscale resolution achieved by the model allowed the spatial and temporal evolution of the changing flow patterns, triggered by internal dynamics, to be followed in detail. This modelling effort has initiated the treatment of the open boundary conditions problem in view of the future implementation of shelf-scale real-time ocean forecasting through the sequential nesting of a hierarchy of successively embedded model domains for the downscaling of the hydrodynamics from the coarse grid Ocean General Circulation Model of the whole Mediterranean Sea to finer grids in coastal areas. Key words. Oceanography: general (continental shelf processes; numerical modelling) Oceanography: physical (general circulation)

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

Ocean Science Discussions ◽

10.5194/osd-3-637-2006 ◽

2006 ◽

Vol 3 (3) ◽

pp. 637-669 ◽

Cited By ~ 8

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.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0142.1 ◽

2018 ◽

Vol 48 (5) ◽

pp. 1139-1150 ◽

Cited By ~ 5

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.

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Can Lagrangian Tracking Simulate Tracer Spreading in a High-Resolution Ocean General Circulation Model?

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0152.1 ◽

2019 ◽

Vol 49 (5) ◽

pp. 1141-1157 ◽

Cited By ~ 6

Author(s):

Patrick Wagner ◽

Siren Rühs ◽

Franziska U. Schwarzkopf ◽

Inga Monika Koszalka ◽

Arne Biastoch

Keyword(s):

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Eddy Diffusivity ◽

Ocean General Circulation Model ◽

Horizontal Resolution ◽

Ocean Model ◽

Time Step ◽

Lagrangian Particles ◽

Cape Basin

AbstractTo model tracer spreading in the ocean, Lagrangian simulations in an offline framework are a practical and efficient alternative to solving the advective–diffusive tracer equations online. Differences in both approaches raise the question of whether both methods are comparable. Lagrangian simulations usually use model output averaged in time, and trajectories are not subject to parameterized subgrid diffusion, which is included in the advection–diffusion equations of ocean models. Previous studies focused on diffusivity estimates in idealized models but could show that both methods yield similar results as long as the deformations-scale dynamics are resolved and a sufficient amount of Lagrangian particles is used. This study compares spreading of an Eulerian tracer simulated online and a cloud of Lagrangian particles simulated offline with velocities from the same ocean model. We use a global, eddy-resolving ocean model featuring 1/20° horizontal resolution in the Agulhas region around South Africa. Tracer and particles were released at one time step in the Cape Basin and below the mixed layer and integrated for 3 years. Large-scale diagnostics, like mean pathways of floats and tracer, are almost identical and 1D horizontal distributions show no significant differences. Differences in vertical distributions, seen in a reduced vertical spreading and downward displacement of particles, are due to the combined effect of unresolved subdaily variability of the vertical velocities and the spatial variation of vertical diffusivity. This, in turn, has a small impact on the horizontal spreading behavior. The estimates of eddy diffusivity from particles and tracer yield comparable results of about 4000 m2 s−1 in the Cape Basin.

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Frontogenesis in the Agulhas Return Current Region Simulated by a High-Resolution CGCM

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0038.1 ◽

2017 ◽

Vol 47 (11) ◽

pp. 2691-2710 ◽

Cited By ~ 6

Author(s):

Shun Ohishi ◽

Tomoki Tozuka ◽

Meghan F. Cronin

Keyword(s):

High Resolution ◽

Mixed Layer ◽

General Circulation ◽

Circulation Model ◽

Frontal Region ◽

Return Current ◽

Sst Front ◽

Vorticity Advection ◽

Southern Side ◽

The Mean

AbstractDetailed mechanisms for frontogenesis/frontolysis of the sea surface temperature (SST) front in the Agulhas Return Current (ARC) region are investigated using outputs from a high-resolution coupled general circulation model. The SST front is maintained throughout the year through an approximate balance between frontolysis by surface heat flux and frontogenesis by horizontal advection. Although a southward (northward) cross-isotherm flow on the northern (southern) side of the front is weaker than a strong eastward along-isotherm current in the frontal region, this cross-isotherm confluent flow advects warmer (cooler) temperature toward the SST front north (south) of the front and acts as the dominant frontogenesis mechanism. In addition, stronger (weaker) frontogenesis in austral summer (winter) is attributed to the stronger (weaker) cross-isotherm confluence, which may be linked to seasonal variations of the Agulhas Current, ARC, and Antarctic Circumpolar Current. On the other hand, the contribution from entrainment is relatively small, because frontolysis by larger (smaller) entrainment velocity on the northern (southern) side opposes frontogenesis by less (more) effective cooling associated with a thicker (thinner) mixed layer and smaller (larger) temperature difference between the mixed layer and entrained water in the northern (southern) region. To gain further insight into the time-mean cross-isotherm confluent flow in the frontal region, the vorticity balance is examined. It is shown that anticyclonic (cyclonic) vorticity advection north (south) of the front by the mean cross-isotherm confluence is in balance with the sum of cyclonic (anticyclonic) vorticity advection by the mean along-isotherm flow and cross-isotherm eddy–mean interaction.

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The Contribution of Striations to the Eddy Energy Budget and Mixing: Diagnostic Frameworks and Results in a Quasigeostrophic Barotropic System with Mean Flow

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0199.1 ◽

2015 ◽

Vol 45 (8) ◽

pp. 2095-2113 ◽

Cited By ~ 4

Author(s):

Ru Chen ◽

Glenn R. Flierl

Keyword(s):

Large Scale ◽

Low Frequency ◽

Ocean Model ◽

Invariance Property ◽

Mean Flow ◽

Eddy Diffusivities ◽

Energy Cascades ◽

The Mean ◽

Flow Theories ◽

Noise Forcing

AbstractLow-frequency oceanic motions have banded structures termed “striations.” Since these striations embedded in large-scale gyre flows can have large amplitudes, the authors investigated the effect of mean flow on their directions as well as their contribution to energetics and mixing using a β-plane, barotropic, quasigeostrophic ocean model. In spite of the model simplicity, striations are always found to exist regardless of the imposed barotropic mean flow. However, their properties are sensitive to the mean flow. Rhines jets move with the mean flow and are not necessarily striations. If the meridional component of the mean flow is large, Rhines jets become high-frequency motions; low-frequency striations still exist, but they are nonzonal, have small magnitudes, and contribute little to energetics and mixing. Otherwise, striations are zonal, dominated by Rhines jets, and contribute significantly to energetics and mixing. This study extends the theory of β-plane, barotropic turbulence, driven by white noise forcing at small scales, to include the effect of a constant mean flow. Theories developed in this study, based upon the Galilean invariance property, illustrate that the barotropic mean flow has no effect on total mixing rates, but does affect the energy cascades in the frequency domain. Diagnostic frameworks developed here can be useful to quantify the striations’ contribution to energetics and mixing in the ocean and more realistic models. A novel diagnostic formula is applied to estimating eddy diffusivities.

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Effects of Tropical Cyclones on Ocean Heat Transport in a High-Resolution Coupled General Circulation Model

Journal of Climate ◽

10.1175/2011jcli4104.1 ◽

2011 ◽

Vol 24 (16) ◽

pp. 4368-4384 ◽

Cited By ~ 208

Author(s):

Enrico Scoccimarro ◽

Silvio Gualdi ◽

Alessio Bellucci ◽

Antonella Sanna ◽

Pier Giuseppe Fogli ◽

...

Keyword(s):

Twentieth Century ◽

High Resolution ◽

Heat Transport ◽

Tropical Cyclones ◽

General Circulation Model ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Ocean Heat Transport ◽

Coupled General Circulation Model

Abstract In this paper the interplay between tropical cyclones (TCs) and the Northern Hemispheric ocean heat transport (OHT) is investigated. In particular, results from a numerical simulation of the twentieth-century and twenty-first-century climates, following the Intergovernmental Panel on Climate Change (IPCC) twentieth-century run (20C3M) and A1B scenario protocols, respectively, have been analyzed. The numerical simulations have been performed using a state-of-the-art global atmosphere–ocean–sea ice coupled general circulation model (CGCM) with relatively high-resolution (T159) in the atmosphere. The CGCM skill in reproducing a realistic TC climatology has been assessed by comparing the model results from the simulation of the twentieth century with available observations. The model simulates tropical cyclone–like vortices with many features similar to the observed TCs. Specifically, the simulated TCs exhibit realistic structure, geographical distribution, and interannual variability, indicating that the model is able to capture the basic mechanisms linking the TC activity with the large-scale circulation. The cooling of the surface ocean observed in correspondence of the TCs is well simulated by the model. TC activity is shown to significantly increase the poleward OHT out of the tropics and decrease the poleward OHT from the deep tropics on short time scales. This effect, investigated by looking at the 100 most intense Northern Hemisphere TCs, is strongly correlated with the TC-induced momentum flux at the ocean surface, where the winds associated with the TCs significantly weaken (strengthen) the trade winds in the 5°–18°N (18°–30°N) latitude belt. However, the induced perturbation does not impact the yearly averaged OHT. The frequency and intensity of the TCs appear to be substantially stationary through the entire 1950–2069 simulated period, as does the effect of the TCs on the OHT.

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The GPU version of LASG/IAP Climate System Ocean Model version 3 (LICOM3) under the heterogeneous-compute interface for portability (HIP) framework and its large-scale application

Geoscientific Model Development ◽

10.5194/gmd-14-2781-2021 ◽

2021 ◽

Vol 14 (5) ◽

pp. 2781-2799

Author(s):

Pengfei Wang ◽

Jinrong Jiang ◽

Pengfei Lin ◽

Mengrong Ding ◽

Junlin Wei ◽

...

Keyword(s):

General Circulation ◽

Large Scale ◽

Vertical Direction ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Ocean Model ◽

Climate System ◽

Global Ocean ◽

Processing Unit ◽

Model Version

Abstract. A high-resolution (1/20∘) global ocean general circulation model with graphics processing unit (GPU) code implementations is developed based on the LASG/IAP Climate System Ocean Model version 3 (LICOM3) under a heterogeneous-compute interface for portability (HIP) framework. The dynamic core and physics package of LICOM3 are both ported to the GPU, and three-dimensional parallelization (also partitioned in the vertical direction) is applied. The HIP version of LICOM3 (LICOM3-HIP) is 42 times faster than the same number of CPU cores when 384 AMD GPUs and CPU cores are used. LICOM3-HIP has excellent scalability; it can still obtain a speedup of more than 4 on 9216 GPUs compared to 384 GPUs. In this phase, we successfully performed a test of 1/20∘ LICOM3-HIP using 6550 nodes and 26 200 GPUs, and on a large scale, the model's speed was increased to approximately 2.72 simulated years per day (SYPD). By putting almost all the computation processes inside GPUs, the time cost of data transfer between CPUs and GPUs was reduced, resulting in high performance. Simultaneously, a 14-year spin-up integration following phase 2 of the Ocean Model Intercomparison Project (OMIP-2) protocol of surface forcing was performed, and preliminary results were evaluated. We found that the model results had little difference from the CPU version. Further comparison with observations and lower-resolution LICOM3 results suggests that the 1/20∘ LICOM3-HIP can reproduce the observations and produce many smaller-scale activities, such as submesoscale eddies and frontal-scale structures.

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Seasonal and interannual variability of physical and biological dynamics at the Shelfbreak Front of the Middle Atlantic Bight: nutrient supply mechanisms

Biogeosciences Discussions ◽

10.5194/bgd-8-1555-2011 ◽

2011 ◽

Vol 8 (1) ◽

pp. 1555-1590 ◽

Cited By ~ 1

Author(s):

R. He ◽

K. Chen ◽

K. Fennel ◽

G. G. Gawarkiewicz ◽

Keyword(s):

Interannual Variability ◽

Water Column ◽

Circulation Model ◽

Deep Ocean ◽

Nutrient Supply ◽

Early Summer ◽

Late Winter ◽

Middle Atlantic Bight ◽

Seasonal And Interannual Variability ◽

Middle Atlantic

Abstract. A size-structured ecosystem model is coupled to a 3-dimensional, high-resolution circulation model to investigate the seasonal and interannual variability of physical and biological states and their driving mechanisms at the shelfbreak front of the Middle Atlantic Bight (MAB). Simulated surface chlorophyll fields compare favorably to the satellite observations and capture the shelfbreak biomass enhancement, which is one of the essential biological features of the region. The domain-wide upper water column nutrient content peaks in late winter-early spring. The phytoplankton spring bloom starts 1–2 months later, followed by a zooplankton bloom in early summer. Seasonal and interannual variability in hindcast shelfbreak nutrient supply is controlled by three processes: (1) local mixing that deepens the mixed layer and injects deep ocean nutrients into the upper water column; (2) alongshore nutrient transport by the shelfbreak jet and associated currents; and (3) nutrient upwelling associated with shelfbreak bottom boundary layer convergence. Interannual variability of physical and biological processes are highlighted by cross-shelf nutrient budget diagnostics for spring 2004 and 2007, which show not only complex vertical structure of various dynamical terms, but also significant variations in magnitude between the two years.

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