References of "Weisberg, Robert H."
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See detailThermocline characterisation in the Cariaco basin: A modelling study of the thermocline annual variation and its relation with winds and chlorophyll-a concentration
Alvera Azcarate, Aïda ULiege; Barth, Alexander ULiege; Weisberg, Robert H. et al

in Continental Shelf Research (2011), 31(1), 73-84

The spatial and temporal evolution of the thermocline depth and width of the Cariaco basin (Venezuela) is analysed by means of a three-dimensional hydrodynamic model. The thermocline depth and width are ... [more ▼]

The spatial and temporal evolution of the thermocline depth and width of the Cariaco basin (Venezuela) is analysed by means of a three-dimensional hydrodynamic model. The thermocline depth and width are determined through the fitting of model temperature profiles to a sigmoid function. The use of whole profiles for the fitting allows for a robust estimation of the thermocline characteristics, mainly width and depth. The fitting method is compared to the maximum gradient approach, and it is shown that, under some circumstances, the method presented in this work leads to a better characterization of the thermocline. After assessing, through comparison with independent {\it in situ} data, the model capabilities to reproduce the Cariaco basin thermocline, the seasonal variability of this variable is analysed, and the relationship between the annual cycle of the thermocline depth, the wind field and the distribution of chlorophyll-a concentration in the basin is studied. The interior of the basin reacts to easterly winds intensification with a rising of the thermocline, resulting in a coastal upwelling response, with the consequent increase in chlorophyll-a concentration. Outside the Cariaco basin, where an open-ocean, oligothrophic regime predominates, wind intensification increases mixing of the surface layers and induces therefore a deepening of the thermocline. The seasonal cycle of the thermocline variability in the Cariaco basin is therefore related to changes in the wind field. At shorter time scales (i.e. days), it is shown that other processes, such as the influence of the meandering Caribbean Current, can also influence the thermocline variability. The model thermocline depth is shown to be in good agreement with the two main ventilation events that took place in the basin during the period of the simulation. [less ▲]

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See detailCariaco basin dynamics: Study of the thermocline depth variability and its relation with open ocean conditions
Alvera Azcarate, Aïda ULiege; Barth, Alexander ULiege; Weisberg, Robert H. et al

Conference (2010, August 11)

The Cariaco basin (Venezuela) is a semi-enclosed trench located along the coast of Venezuela, with maximum depths of about 1400 m. It is connected to the open ocean by two shallow passages of less than ... [more ▼]

The Cariaco basin (Venezuela) is a semi-enclosed trench located along the coast of Venezuela, with maximum depths of about 1400 m. It is connected to the open ocean by two shallow passages of less than 150 m depth. Limited basin ventilation, coupled with a small vertical mixing results in anoxic conditions from about 250 m to the bottom. The dynamics of the Cariaco Basin are studied by means of a three-dimensional hydrodynamic model. The numerical model has a resolution of 1/60 degree and is an implementation of the Regional Ocean Modeling System (ROMS) nested in the global HYCOM solution from the Naval Research Laboratory. Of particular interest are the mechanisms that link the basin's interior to the Caribbean Sea, which can lead to the ventilation of the basin's anoxic sub-surface waters. To assess the influence of the open ocean on the basin, the spatial and temporal evolution of the thermocline depth and width is studied, as well as its relationship with wind variability and chlorophyll-a concentration: at seasonal scales, the interior of the basin reacts to easterly winds intensification with a rising of the thermocline, resulting in a coastal upwelling response, with the consequent increase in chlorophyll-a concentration. Outside the Cariaco basin, where an open-ocean, oligotrophic regime predominates, wind intensification increases mixing of the surface layers and induces therefore a deepening of the thermocline. At shorter time scales (i.e. days), it is shown that other processes, such as the influence of the meandering Caribbean Current, can also influence the thermocline variability within the Cariaco basin. [less ▲]

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See detailEnsemble-based assimilation of high-frequency radar surface currents in regional ocean models
Barth, Alexander ULiege; Alvera Azcarate, Aïda ULiege; Beckers, Jean-Marie ULiege et al

Conference (2010)

The results of coastal ocean models depend critically on the accuracy of boundary and initial conditions and atmospheric forcing. The precision of coastal ocean models is limited among others by ... [more ▼]

The results of coastal ocean models depend critically on the accuracy of boundary and initial conditions and atmospheric forcing. The precision of coastal ocean models is limited among others by uncertainty in those forcing fields. Since high-frequency (HF) radar installations provide measurements over a relatively large area, the assimilation of these data has a high potential to reduce the errors in ocean models and to provide a dynamically consistent estimation of the ocean circulation. The assimilation of HF radar data is not without its own challenges: the spatial variation of the surface currents uncertainty, the high temporal resolution of HF radar data, the simultaneous presence of a wide range of processes with distinct spatial and temporal scales (tides and other surface gravity waves, mesoscale and wind-driven circulation), and the generally strong sensitivity of regional models to errors in the boundary conditions and atmospheric forcings. These processess are important aspects to consider in the application of data assimilation methods to HF radar measurements. The results of two data assimilation experiments on the West Florida Shelf (WFS) and the German Bight are presented. HF radar currents are assimilated in a nested West Florida Shelf based on an ensemble of model realizations with different wind forcings. The model is sequentially updated and a filter is implemented to reduce spurious surface-gravity waves. Results of the WFS model assimilating surface currents show an improvement of the model currents not only at the surface but also at depth compared to independent ADCP observations. This West Florida Shelf assimilation experiment does not include tides. Tides are not generated within the domain, but are rather propagated inside the domain through the boundary conditions. The potential of using HF radar data to reduce errors in tidal boundary conditions is shown in a model setup of the German Bight. For improving the modeled tidal variability it is not sufficient to update the model state without updating the boundary conditions. An ensemble smoother to improve the tidal boundary values is presented and validated with independent HF radar measurements and tide-gage data. The ensemble-scheme is also applied to improve the wind forcing by assimilation of surface currents. The improvement of the analyzed wind forcing is assessed by using in-situ wind measurements. [less ▲]

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See detailThe Surface Circulation of the Caribbean Sea and the Gulf of Mexico as Inferred from Satellite Altimetry
Alvera Azcarate, Aïda ULiege; Barth, Alexander ULiege; Weisberg, Robert H.

in Journal of Physical Oceanography (2009), 39(3), 640657

The surface circulation of the Caribbean Sea and Gulf of Mexico is studied using 13 years of satellite altimetry data. Variability in the Caribbean Sea is evident over several time scales. At the annual ... [more ▼]

The surface circulation of the Caribbean Sea and Gulf of Mexico is studied using 13 years of satellite altimetry data. Variability in the Caribbean Sea is evident over several time scales. At the annual scale, sea surface height (SSH) varies mainly by a seasonal steric effect. Interannually, a longer cycle affects the SSH slope across the current and hence the intensity of the Caribbean Current. This cycle is found to be related to changes in the wind intensity, the wind stress curl, and El Niño–Southern Oscillation. At shorter time scales, eddies and meanders are observed in the Caribbean Current, and their propagation speed is explained by baroclinic instabilities under the combined effect of vertical shear and the β effect. Then the Loop Current (LC) is considered, focusing on the anticyclonic eddies shed by it and the intrusion of the LC into the Gulf of Mexico through time. Twelve of the 21 anticyclonic eddies observed to detach from the LC are shed from July to September, suggesting a seasonality in the timing of these events. Also, a relation is found between the intrusion of the LC into the Gulf of Mexico and the size of the eddies shed from it: larger intrusions trigger smaller eddies. A series of extreme LC intrusions into the Gulf of Mexico, when the LC is observed as far as 92°W, are described. The analyses herein suggest that the frequency of such events has increased in recent years, with only one event occurring in 1993 versus three from 2002 to 2006. Transport through the Straits of Florida appears to decrease during these extreme intrusions. [less ▲]

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See detailA nested model of the Cariaco Basin (Venezuela): description of the basin’s interior hydrography and interactions with the open ocean
Alvera Azcarate, Aïda ULiege; Barth, Alexander ULiege; Weisberg, Robert H.

in Ocean Dynamics (2009), 59(1), 97-120

A high-resolution (1/60°), three-dimensional numerical circulation model of the Cariaco Basin (Venezuela) is constructed by nesting the Regional Ocean Modeling System (ROMS) in the 1/12° global Hybrid ... [more ▼]

A high-resolution (1/60°), three-dimensional numerical circulation model of the Cariaco Basin (Venezuela) is constructed by nesting the Regional Ocean Modeling System (ROMS) in the 1/12° global Hybrid Coordinate Ocean Model (HYCOM). A new bathymetry, computed by merging DBDB2 data and in situ depth measurements using optimal interpolation, is described. This new bathymetry corrects the depth of the channels that connect the Cariaco Basin with the open ocean and which play a very important role in the basin circulation. Results from a 2004 ROMS hindcast are presented. Observations (temperature, salinity, and currents) are used to validate the model results before using the model to describe the annual cycle of the Cariaco Basin and the interactions between the basin and the open ocean. Two modes of interaction are described, the first being the meanders and eddies that travel westward with the Caribbean Current, and the second being a subsurface eastward current that flows along the north coast of South America. The circulation path within the basin is directly related to the intensity of this current. Both mechanisms described play a role in the ventilation of the basin. The present study is also an example of the feasibility of one of the objectives of GODAE (Global Ocean Data Assimilation Experiment): downscaling from a large-scale model to a regional model. In particular, the nesting ratio of 5 used in this work demonstrates that a high-resolution model can be successfully nested in HYCOM. [less ▲]

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See detailMultivariate reconstruction of missing data in sea surface temperature, chlorophyll, and wind satellite fields
Alvera Azcarate, Aïda ULiege; Barth, Alexander ULiege; Beckers, Jean-Marie ULiege et al

in Journal of Geophysical Research. Oceans (2007), 112(C3), 03008

An empirical orthogonal function–based technique called Data Interpolating Empirical Orthogonal Functions (DINEOF) is used in a multivariate approach to reconstruct missing data. Sea surface temperature ... [more ▼]

An empirical orthogonal function–based technique called Data Interpolating Empirical Orthogonal Functions (DINEOF) is used in a multivariate approach to reconstruct missing data. Sea surface temperature (SST), chlorophyll a concentration, and QuikSCAT winds are used to assess the benefit of a multivariate reconstruction. In particular, the combination of SST plus chlorophyll, SST plus lagged SST plus chlorophyll, and SST plus lagged winds have been studied. To assess the quality of the reconstructions, the reconstructed SST and winds have been compared to in situ data. The combination of SST plus chlorophyll, as well as SST plus lagged SST plus chlorophyll, significantly improves the results obtained by the reconstruction of SST alone. All the experiments correctly represent the SST, and an upwelling/downwelling event in the West Florida Shelf reproduced by the reconstructed data is studied. [less ▲]

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