Martin Saraceno
National Scientific and Technical Research Council
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Featured researches published by Martin Saraceno.
Journal of Geophysical Research | 2008
Martin Saraceno; P. T. Strub; P. M. Kosro
[1] Present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height (SSH) in the nearshore region, resulting in a measurement gap of 25–50 km next to the coast. In the present work, gridded SSH fields produced by Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) in the offshore region are combined with coastal tide gauge time series of SSH to improve estimation in that gap along the west coast of the United States in the northern California Current System between 40 and 45N and 123.8 and 126W. To assess the increase in skill provided by this procedure, the geostrophic alongshore currents, calculated from the new SSH fields in the gap region, are compared to three in situ, nearshore current measurements, resulting in correlation coefficients of 0.73–0.83 and standard deviations of the differences of 11.6–12.6 cm/s, substantially improved from the AVISO-only results. When the Ekman current components are estimated and added to the geostrophic currents, comparisons to the 10 m deep acoustic Doppler current profiler velocities are only slightly improved. The Ekman components make a more significant contribution when compared to HF radar surface current measurements, providing correlations of 0.94 and standard deviations of the differences of 6.4–9.5 cm/s. These results represent a dramatic improvement in the quality of the SSH fields and estimated alongshore currents when additional, realistic SSH data from the coastal region are added. Here we use coastal tide gauges to provide the additional SSH data but also discuss more general approaches for altimeter SSH retrievals in coastal regions where tide gauge data are not available.
Journal of Geophysical Research | 2014
Raul A. Guerrero; Alberto R. Piola; Harold Fenco; Ricardo P. Matano; Vincent Combes; Yi Chao; Corinne James; Elbio D. Palma; Martin Saraceno; P. Ted Strub
Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35°S. Away from the tropics, these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-defined seasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelf waters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36°S to 37°30′S). In contrast, in fall and winter, low-salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters in the open ocean. Key Points Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies
Journal of Geophysical Research | 2015
P. Ted Strub; Corinne James; Vincent Combes; Ricardo P. Matano; Alberto R. Piola; Elbio D. Palma; Martin Saraceno; Raul A. Guerrero; Harold Fenco; Laura A. Ruiz‐Etcheverry
Abstract Altimeter sea surface height (SSH) fields are analyzed to define and discuss the seasonal circulation over the wide continental shelf in the SW Atlantic Ocean (27°–43°S) during 2001–2012. Seasonal variability is low south of the Rio de la Plata (RdlP), where winds and currents remain equatorward for most of the year. Winds and currents in the central and northern parts of our domain are also equatorward during autumn and winter but reverse to become poleward during spring and summer. Transports of shelf water to the deep ocean are strongest during summer offshore and to the southeast of the RdlP. Details of the flow are discussed using mean monthly seasonal cycles of winds, heights, and currents, along with analyses of Empirical Orthogonal Functions. Principle Estimator Patterns bring out the patterns of wind forcing and ocean response. The largest part of the seasonal variability in SSH signals is due to changes in the wind forcing (described above) and changes in the strong boundary currents that flow along the eastern boundary of the shelf. The rest of the variability contains a smaller component due to heating and expansion of the water column, concentrated in the southern part of the region next to the coast. Our results compare well to previous studies using in situ data and to results from realistic numerical models of the regional circulation.
Journal of Geophysical Research | 2014
Ricardo P. Matano; Vincent Combes; Alberto R. Piola; Raul A. Guerrero; Elbio D. Palma; P. Ted Strub; Corinne James; Harold Fenco; Yi Chao; Martin Saraceno
A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA), the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high-frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.
Journal of Geophysical Research | 2016
Camila Artana; Ramiro Ferrari; Zoé Koenig; Martin Saraceno; Alberto R. Piola; Christine Provost
The Malvinas Current (MC) is an offshoot of the Antarctic Circumpolar Current (ACC). Downstream of Drake Passage, the northern fronts of the ACC veer northward, cross over the North Scotia Ridge (NSR) and the Malvinas Plateau, and enter the Argentine Basin. We investigate the variations of the MC circulation between the NSR and 41°S and their possible relations with the ACC circulation using data from Argo floats and satellite altimetry. The data depict meandering and eddy shedding of the northern ACC jets as they cross the NSR. The altimetry fields show that these eddies are trapped, break down, and dissipate over the Malvinas Plateau, suggesting that this region is a hot spot for dissipation of mesoscale variability. Variations of sea level anomalies (SLA) across the NSR do not impact the MC further north, except for intra-seasonal variability associated with coastal trapped waves. Altimetry and float trajectories show events during which a large fraction of the MC is cut off from the ACC. Blocking events at around 48.5°S are a recurrent feature of the MC circulation. Over the 23 year altimetry record, we detected 26 events during which the MC surface transport at 48.5°S was reduced to less than half its long-term mean. Blocking events last from 10 to 35 days and do not present any significant trend. These events were tracked back to positive SLA that built up over the Argentine Abyssal Plain. Future work is needed to understand the processes responsible for these blocking events.
Journal of Geophysical Research | 2016
L. A. Ruiz Etcheverry; Martin Saraceno; Alberto R. Piola; P. T. Strub
Abstract We study the annual patterns and linear trend of satellite sea level anomaly (SLA) over the southwest South Atlantic continental shelf (SWACS) between 54ºS and 36ºS. Results show that south of 42°S the thermal steric effect explains nearly 100% of the annual amplitude of the SLA, while north of 42°S it explains less than 60%. This difference is due to the halosteric contribution. The annual wind variability plays a minor role over the whole continental shelf. The temporal linear trend in SLA ranges between 1 and 5 mm/yr (95% confidence level). The largest linear trends are found north of 39°S, at 42°S and at 50°S. We propose that in the northern region the large positive linear trends are associated with local changes in the density field caused by advective effects in response to a southward displacement of the South Atlantic High. The causes of the relative large SLA trends in two southern coastal regions are discussed as a function meridional wind stress and river discharge. Finally, we combined the annual cycle of SLA with the mean dynamic topography to estimate the absolute geostrophic velocities. This approach provides the first comprehensive description of the seasonal component of SWACS circulation based on satellite observations. The general circulation of the SWACS is northeastward with stronger/weaker geostrophic currents in austral summer/winter. At all latitudes, geostrophic velocities are larger (up to 20 cm/s) close to the shelf‐break and decrease toward the coast. This spatio‐temporal pattern is more intense north of 45°S.
Ocean Dynamics | 2015
Paula Etala; Martin Saraceno; Pablo Echevarría
Cyclogenesis and long-fetched winds along the southeastern coast of South America may lead to floods in populated areas, as the Buenos Aires Province, with important economic and social impacts. A numerical model (SMARA) has already been implemented in the region to forecast storm surges. The propagation time of the surge in such extensive and shallow area allows the detection of anomalies based on observations from several hours up to the order of a day prior to the event. Here, we investigate the impact and potential benefit of storm surge level data assimilation into the SMARA model, with the objective of improving the forecast. In the experiments, the surface wind stress from an ensemble prediction system drives a storm surge model ensemble, based on the operational 2-D depth-averaged SMARA model. A 4-D Local Ensemble Transform Kalman Filter (4D-LETKF) initializes the ensemble in a 6-h cycle, assimilating the very few tide gauge observations available along the northern coast and satellite altimeter data. The sparse coverage of the altimeters is a challenge to data assimilation; however, the 4D-LETKF evolving covariance of the ensemble perturbations provides realistic cross-track analysis increments. Improvements on the forecast ensemble mean show the potential of an effective use of the sparse satellite altimeter and tidal gauges observations in the data assimilation prototype. Furthermore, the effects of the localization scale and of the observational errors of coastal altimetry and tidal gauges in the data assimilation approach are assessed.
Journal of Geophysical Research | 2018
Camila Artana; Jean-Michel Lellouche; Young-Hyang Park; Gilles Garric; Zoé Koenig; Nathalie Sennéchael; Ramiro Ferrari; Alberto R. Piola; Martin Saraceno; Christine Provost
We examine the surface and subsurface signature of ocean fronts closely associated with theMalvinas Current dynamics. We first evaluate the performances of the Mercator Ocean eddy permitting (1/128spatial resolution) global operational system in the southwestern Atlantic Ocean over the last 10 years (2007–2016) using satellite, Argo float and in situ data collected near 418S. Observations versus model comparisons show that the model correctly reproduces the general circulation and the complex hydrographic features ofthe study area including the vicinity of the Brazil-Malvinas Confluence. The model outputs accurately match the observations except in June 2015. The causes for the June 2015 mismatch are analyzed. We then used themodel and satellite altimetry to identify isolines of absolute dynamic topography (ADT) and potential densityat different depths associated with the mean front location and establish their correspondence with specificwater mass boundaries. Frontal displacements as depicted in satellite ADT, model ADT, and model potential density at 450 m are in general agreement. The ADT and potential density at 450 m provide nonidentical and complementary information on eddies shed by the Polar Front (PF): while ADT depicts the surface circulation with PF eddies entrained into the energetic circulation over the deep Argentine Basin, potential density at450 m is more effective at monitoring PF eddies feeding the Malvinas Current.
Archive | 2018
Alberto R. Piola; Elbio D. Palma; Alejandro A. Bianchi; Belmiro M. Castro; Marcelo Dottori; Raul A. Guerrero; Marina Marrari; Ricardo P. Matano; Osmar O. MöllerJr; Martin Saraceno
The continental shelf of the western South Atlantic is characterized by three regions subject to distinct oceanographic regimes. The wide subantarctic shelf, south of approximately 35°S, is occupied by cold, low-salinity waters derived from the Subantarctic Zone and further diluted by the inflow of additional low-salinity waters, primarily from the Magellan Strait. Farther north, the shelf narrows considerably and is subject to the influence of large freshwater discharges and warm-salty intrusions of subtropical waters from the Brazil Current. Intense frontal transitions at various near shore locations and along the shelf break promote vertical circulations that inject nutrients into the upper layer. This nutrient injection leads to enhanced growth of phytoplankton, and, in some regions, to a significant uptake of atmospheric CO2. While the subantarctic shelf is under the influence of strong westerlies and high-amplitude tides, most of the subtropical shelf undergoes seasonally reversing winds and a micro-tidal regime. The shelf characteristics are also influenced by the offshore circulation, which is dominated by the equatorward flow of cold, nutrient-rich waters of the Malvinas Current in the south and the poleward flow of warm, salty, and oligotrophic waters of the Brazil Current in the north. There is a convergent large-scale mean circulation toward the transition between subantarctic and subtropical shelf waters near 34°S, which is balanced by export of shelf waters to the deep ocean. This article describes the contrasting water masses, frontal features, and circulation patterns of this region.
Journal of Geophysical Research | 2018
Guillermina F. Paniagua; Martin Saraceno; Alberto R. Piola; Raul A. Guerrero; Christine Provost; Ramiro Ferrari; Loreley Selene Lago; Camila Artana
The temporal variability of 11 months of in situ velocity, temperature, and salinity data collected at five moorings deployed at 408S–418S across the shelf-break in the Southwestern Atlantic is analyzed. Two distinct regimes characterized by strong and weak along-slope velocities are present. During the strong regime the Malvinas Current flows northward through the moorings while during the nearly 5months long weak regime reversals of the along-slope velocities are frequently observed. Comparison with the previous in situ time series obtained in the same region shows that such an extended period of weak flow has not been previously observed. During the weak regime, Sub-Antarctic Mode Water is observed over the 1,800 m isobath at an average depth of 500 m. Water masses occupying the upper 1,600 m during the strong regime deepen and shift eastward during the weak period. Satellite geostrophic velocities and sea surface temperature clearly show that the weak regime is due to a deflection to the east of the Malvinas Current, upstream of the mooring position. Analysis of the vertical structure of the currents indicate that during the weak regime the flow weakens mostly at the surface and presents a very small vertical shear. In contrast, during the strong regime currents are surface-intensified. The change in the structure of the cur-rents at the mooring location impacts the relationship between in situ and altimetry-derived currents: during the weak regime altimetry adequately represents (rmsd 12 cm/s) in situ currents in the whole water column, while during strong regime rmsd are larger than 15 cm/s below 600 m depth.