scholarly journals Tide assessment for the continental shelf situated in the southwestern Atlantic between the latitudes 19.8ºS and 21.2ºS

2016 ◽  
Vol 64 (2) ◽  
pp. 113-126 ◽  
Author(s):  
Julio Tomás Aquije Chacaltana ◽  
Leonardo Carvalho de Jesus ◽  
Fernando Túlio Camilo Barreto ◽  
Valdir Innocentini
Keyword(s):  
Boundary Conditions ◽  
Continental Shelf ◽  
Local Domain ◽  
Residual Currents ◽  
Astronomical Tide ◽  
Tidal Propagation ◽  
South Central ◽  
Tidal Harmonics ◽  
Phase Amplitude ◽  
Grid Nesting

Abstract The astronomical tide was numerically simulated by the MOHID model for the South-Central Region of Espírito Santo State (Brazil), between latitudes 19.8ºS and 21.2ºS. The grid nesting technique was used to transpose the boundary conditions from the larger domain to a more refined local domain (spatial resolution around 450 m), with tidal harmonics provided by the TPXO tide inverse model as boundary conditions for the larger domain. Results from the numerical model were compared with both the pre-existing tide harmonics and the harmonics calculated from measured data. From the maps of phase, amplitude, tidal ellipses and residual currents the main tidal kinematic characteristics in the study area were described. On the continental shelf, the results showed that the physiography and bathymetry of the region play an important role in the distribution of tidal co-phases, co-amplitudes, ellipses and residual currents. The MOHID model was able to reproduce satisfactorily the astronomical tide and thus can be used to study the behaviour of the tidal propagation in continental shelf areas.

scholarly journals Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

2006 ◽  
Vol 3 (3) ◽  
pp. 291-318
Author(s):  
L. Vandenbulcke ◽  
A. Barth ◽  
M. Rixen ◽  
A. Alvera-Azcárate ◽  
Z. Ben Bouallegue ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Boundary Conditions ◽  
Global Model ◽  
Local Model ◽  
Local Models ◽  
Coastal Zones ◽  
Efficient System ◽  
Nested Models ◽  
Ocean Forecasting ◽  
Grid Nesting

Abstract. Modern operational ocean forecasting systems routinely use data assimilation techniques in order to take observations into account in the hydrodynamic model. Moreover, as end users require higher and higher resolution predictions, especially in coastal zones, it is now common to run nested models, where the coastal model gets its open-sea boundary conditions from a low-resolution global model. This configuration is used in the ''Mediterranean Forecasting System: Towards environmental predictions'' (MFSTEP) project. A global model covering the whole Mediterranean Sea is run weekly, performing 1 week of hindcast and a 10-day forecast. Regional models, using different codes and covering different areas, then use this forecast to implement boundary conditions. Local models in turn use the regional model forecasts for their own boundary conditions. This nested system has proven to be a viable and efficient system to achieve high-resolution weekly forecasts. However, when observations are available in some coastal zone, it remains unclear whether it is better to assimilate them in the global or local model. We perform twin experiments and assimilate observations in the global or in the local model, or in both of them together. We show that, when interested in the local models forecast and provided the global model fields are approximately correct, the best results are obtained when assimilating observations in the local model.

scholarly journals Exploring the impact of atmospheric forcing and basal drag on the Antarctic Ice Sheet under Last Glacial Maximum conditions

2021 ◽  
Vol 15 (1) ◽  
pp. 215-231
Author(s):  
Javier Blasco ◽  
Jorge Alvarez-Solas ◽  
Alexander Robinson ◽  
Marisa Montoya
Keyword(s):  
Boundary Conditions ◽  
Continental Shelf ◽  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Shelf Break ◽  
Ice Volume ◽  
Basal Friction ◽  
The Antarctic ◽  
Continental Shelf Break

Abstract. Little is known about the distribution of ice in the Antarctic Ice Sheet (AIS) during the Last Glacial Maximum (LGM). Whereas marine and terrestrial geological data indicate that the grounded ice advanced to a position close to the continental-shelf break, the total ice volume is unclear. Glacial boundary conditions are potentially important sources of uncertainty, in particular basal friction and climatic boundary conditions. Basal friction exerts a strong control on the large-scale dynamics of the ice sheet and thus affects its size and is not well constrained. Glacial climatic boundary conditions determine the net accumulation and ice temperature and are also poorly known. Here we explore the effect of the uncertainty in both features on the total simulated ice storage of the AIS at the LGM. For this purpose we use a hybrid ice sheet shelf model that is forced with different basal drag choices and glacial background climatic conditions obtained from the LGM ensemble climate simulations of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). Overall, we find that the spread in the simulated ice volume for the tested basal drag parameterizations is about the same range as for the different general circulation model (GCM) forcings (4 to 6 m sea level equivalent). For a wide range of plausible basal friction configurations, the simulated ice dynamics vary widely but all simulations produce fully extended ice sheets towards the continental-shelf break. More dynamically active ice sheets correspond to lower ice volumes, while they remain consistent with the available constraints on ice extent. Thus, this work points to the possibility of an AIS with very active ice streams during the LGM. In addition, we find that the surface boundary temperature field plays a crucial role in determining the ice extent through its effect on viscosity. For ice sheets of a similar extent and comparable dynamics, we find that the precipitation field determines the total AIS volume. However, precipitation is highly uncertain. Climatic fields simulated by climate models show more precipitation in coastal regions than a spatially uniform anomaly, which can lead to larger ice volumes. Our results strongly support using these paleoclimatic fields to simulate and study the LGM and potentially other time periods like the last interglacial. However, their accuracy must be assessed as well, as differences between climate model forcing lead to a large spread in the simulated ice volume and extension.

scholarly journals Early Paleozoic post-breakup magmatism along the Cordilleran margin of western North America: New zircon U-Pb age and whole-rock Nd- and Hf-isotope and lithogeochemical results from the Kechika group, Yukon, Canada

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1262-1290 ◽  
Author(s):  
Roderick W. Campbell ◽  
Luke P. Beranek ◽  
Stephen J. Piercey ◽  
Richard Friedman
Keyword(s):  
North America ◽  
Continental Shelf ◽  
Mantle Source ◽  
Tectonic Setting ◽  
Plate Boundary ◽  
Hf Isotope ◽  
Passive Margin ◽  
Western North America ◽  
South Central ◽  
Cordilleran Margin

AbstractPost-breakup magmatic rocks are recognized features of modern and ancient passive margin successions around the globe, but their timing and significance to non-plume-related rift evolution is generally uncertain. Along the Cordilleran margin of western North America, several competing rift models have been proposed to explain the origins of post-breakup igneous rocks that crop out from Yukon to Nevada. New zircon U-Pb age and whole-rock geochemical studies were conducted on the lower Paleozoic Kechika group, south-central Yukon, to test these rift models and constrain the timing, mantle source, and tectonic setting of post-breakup magmatism in the Canadian Cordillera. The Kechika group contains vent-proximal facies and sediment-sill complexes within the Cassiar platform, a linear paleogeographic high that developed outboard of continental shelf and trough basins. Chemical abrasion (CA-TIMS) U-Pb dates indicate that Kechika group mafic rocks were generated during the late Cambrian (488–483 Ma) and Early Ordovician (473 Ma). Whole-rock trace-element and Nd- and Hf-isotope results are consistent with the low-degree partial melting of an enriched lithospheric mantle source during margin-scale extension. Equivalent continental shelf and trough rocks along western North America are spatially associated with transfer-transform zones and faults that were episodically reactivated during Cordilleran rift evolution. Post-breakup rocks emplaced along the magma-poor North Atlantic margins, including those near the Orphan Knoll and Galicia Bank continental ribbons, are proposed modern analogues for the Kechika group. This scenario calls for the release of in-plane tensile stresses and off-axis, post-breakup magmatism along the nascent plate boundary prior to the onset of seafloor spreading.

scholarly journals Acoustic Doppler Current Profiler observations in the southern Caspian Sea: shelf currents and flow field off Feridoonkenar Bay, Iran

Ocean Science ◽  
2010 ◽  
Vol 6 (3) ◽  
pp. 737-748 ◽  
Author(s):  
P. Ghaffari ◽  
V. Chegini
Keyword(s):  
Flow Field ◽  
Continental Shelf ◽  
Caspian Sea ◽  
Driving Forces ◽  
Acoustic Doppler Current Profiler ◽  
Sea Breeze ◽  
Circulation Pattern ◽  
Current Field ◽  
Astronomical Tide ◽  
Current Profiler

Abstract. The results of offshore bottom-mounted ADCP measurements and wind records carried out from August to September 2003 in the coastal waters off Feridoon-kenar Bay (FB) in the south Caspian Sea (CS) are examined in order to characterize the shelf motion, the steady current field and to determine the main driving forces of currents on the study area. Owing to closed basin and absence of the astronomical tide, the atmospheric forcing plays an important role in the flow field of the CS. The lasting regular sea breeze system is present almost throughout the year. This system performs the forcing in diurnal and semi-diurnal bands similar to tides in other regions. In general, current field in the continental shelf could be separated into two distinguishable schemes, which in cross-shelf direction is dominated by high frequencies (1 cpd and higher frequencies), and in along-shelf orientation mostly proportional to lower frequencies in synoptic weather bands. Long-period wave currents, whose velocities are much greater than those of direct wind-induced currents, dominates the current field in the continental shelf off FB. The propagation of the latter could be described in terms of shore-controlled waves that are remotely generated and travel across the shelf in the southern CS. It has also been shown that long term displacements in this area follow the classic cyclonic, circulation pattern in the southern CS.

Immersive boundary conditions: Theory, implementation, and examples

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. T97-T110 ◽  
Author(s):  
Filippo Broggini ◽  
Marlies Vasmel ◽  
Johan O. A. Robertsson ◽  
Dirk-Jan van Manen
Keyword(s):  
Wave Propagation ◽  
Boundary Conditions ◽  
Seismic Wave Propagation ◽  
Local Domain ◽  
Time Step ◽  
Local Modeling ◽  
Numerical Precision ◽  
Computational Geophysics ◽  
Wavefield Extrapolation ◽  
Full Domain

Many applications in computational geophysics involve the modeling of seismic wave propagation on a set of closely related subsurface models. In such scenarios, it is of interest to recompute the seismic wavefields locally (only in the regions of change), instead of in the full subsurface model. We have developed a method for local acoustic wavefield recomputation that makes it possible to fully immerse a local modeling domain within a larger domain of arbitrary extent and complexity, such that the wave propagation in the full domain is completely accounted for. The method enables wavefield modeling on much smaller local domains, while relying on the up-front generation of a large number of Green’s functions and a wavefield extrapolation step at each time step of the simulation. A Kirchhoff-Helmholtz extrapolation integral is used to predict the interaction of the wavefield leaving the local domain with the exterior domain. The outward propagating wavefield and the wavefield reentering the local domain are applied as a boundary condition along the edges. Thanks to these dynamically calculated boundary conditions, all higher order long-range interactions between the two domains are fully accounted for. We have implemented the method in a conventional finite-difference time-domain scheme and determined that the locally calculated wavefields are equal to wavefields generated on the full domain to within numerical precision. The efficiency of the local modeling algorithm will greatly depend on the nature and size of the problem.

scholarly journals Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

Ocean Science ◽  
2006 ◽  
Vol 2 (2) ◽  
pp. 213-222 ◽  
Author(s):  
L. Vandenbulcke ◽  
A. Barth ◽  
M. Rixen ◽  
A. Alvera-Azcarate ◽  
Z. Ben Bouallegue ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Boundary Conditions ◽  
Global Model ◽  
Local Model ◽  
Local Models ◽  
Coastal Zones ◽  
Efficient System ◽  
Nested Models ◽  
Ocean Forecasting ◽  
Grid Nesting

Abstract. Modern operational ocean forecasting systems routinely use data assimilation techniques in order to take observations into account in the hydrodynamic model. Moreover, as end users require higher and higher resolution predictions, especially in coastal zones, it is now common to run nested models, where the coastal model gets its open-sea boundary conditions from a low-resolution global model. This configuration is used in the "Mediterranean Forecasting System: Towards environmental predictions" (MFSTEP) project. A global model covering the whole Mediterranean Sea is run weekly, performing 1 week of hindcast and a 10-day forecast. Regional models, using different codes and covering different areas, then use this forecast to implement boundary conditions. Local models in turn use the regional model forecasts for their own boundary conditions. This nested system has proven to be a viable and efficient system to achieve high-resolution weekly forecasts. However, when observations are available in some coastal zone, it remains unclear whether it is better to assimilate them in the global or local model. We perform twin experiments and assimilate observations in the global or in the local model, or in both of them together. We show that, when interested in the local models forecast and provided the global model fields are approximately correct, the best results are obtained when assimilating observations in the local model.

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