Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea: A comparison with tide gauges

The new gridded Mediterranean sea level anomaly product recently released by AVISO (DT14) is evaluated and compared with the earlier version (DT10) at which it is aimed to substitute. Differences between the two products are found along coastal regions, where the new version captures more variability (up to 10% more) and trends locally differ by up to 1 mm/yr for the altimetric period. Coastal tide gauge observations have therefore been used as the basis for quantifying changes in DT14. Correlation and variance reduction in available monthly tide gauge time series are improved in more than 80% of the selected sites by up to 0.2 and 5 cm2, respectively. This resulted in an overall higher skill to recover coastal low frequency (with periods larger than a few months) sea level signals. Results for higher/lower order percentiles were also explored and showed different performances depending on the site, although with a slight overall improvement. A comparison with tide gauges on a daily basis using wavelet analysis reveals that altimetry gridded products are not capable of recovering higher frequency (a few days) coastal sea level signals despite some advances have been achieved thanks to the daily temporal sampling of DT14M. Marcos acknowledges a “Ramon y Cajal” contract funded by the Spanish Ministry of Economy. Funding from the MyOcean-Follow-On project (PRE-OPERATIONAL MARINE CONTINUITY IN TRANSITION TOWARDS COPERNICUS- H2020-SPACE/0003) is acknowledgedPeer Reviewe

Coastal Ocean Forecasting: system integration and evaluation

Kourafalou, V.H. et al.ecent advances in Coastal Ocean Forecasting Systems (COFS) are discussed. Emphasis is given to the integration of the observational and modeling components, each developed in the context of monitoring and forecasting in the coastal seas. These integrated systems must be linked to larger scale systems toward seamless data sets, nowcasts and forecasts (from the global ocean, through the continental shelf and to the nearshore regions). Emerging capabilities include: methods to optimize coastal/regional observational networks; and probabilistic approaches to address both science and applications related to COFS. International collaboration is essential to exchange best practices, achieve common frameworks and establish standards.V. Kourafalou acknowledges support from NOAA (NA13OAR4830224 and NA11NOS4780045). M. Herzfeld is thankful to the eReefs marine modeling team and partners (CSIRO: Commonwealth Industrial and Scientific Research Organization; SIEF: Science and Industry Endowment Fund; AIMS: Australian Institute of Marine Science). The system CGOFS_ECS (material contributed by X. Zhu) is supported by the National Natural Science Foundation of China (contract #41222038). E. V. Stanev acknowledges the input from COSYNA, which is supported by the Helmholtz Association of German Research CentersPeer Reviewe

Heavy Guadalquivir River discharge detection with satellite altimetry: The case of the eastern continental shelf of the Gulf of Cadiz (Iberian Peninsula)

© 2015 COSPAR. Published by Elsevier Ltd. All rights reserved. In situ water levels in the Guadalquivir River estuary mouth show the effect of strong river freshwater discharges on the monthly means of the sea level on a yearly basis. Accurate altimeter products oriented toward coastal zones are increasing the number of potential applications at different spatiotemporal scales. The present work is focused on the analysis of the sea-level variability in the eastern shelf of the Gulf of Cadiz (between North Africa and the southwestern side of the Iberian Peninsula), adjacent to the Guadalquivir River estuary. Sixteen years (1994-2009) of along-track and standard AVISO maps of sea-level anomalies (SLAs) have been used to generate a new high-resolution product with increased spatiotemporal resolution. The use of a bathymetry constraint and smaller correlation scales in the methodology developed to generate high-resolution altimeter products improves the characterization of the mesoscale signals in the coastal strip adjacent to the estuary due to strong river freshwater discharges. This has been confirmed by the analysis of along-track SLA data in the vicinity of the estuary. The daily evolution (2 weeks) of the sea level obtained in the event of December 2009 might be related to the river plume extension observed by optical Moderate Resolution Imaging Spectrometer (MODIS) images. The spatiotemporal distribution of the altimeter tracks available in the study area might compromise the mapping capabilities to capture coastal and fine-scale features.This work has been partially supported by the ALCOVA Project (CTM2012-37839) funded by the Spanish Ministerio de Economía y Competitividad and FEDERPeer Reviewe

Surface circulation in the Alborn Sea (western Mediterranean) inferred from remotely sensed data

In this study, for the first time at regional scale, the combined use of remote sensing data (altimetry and sea surface temperature records) provides a description of the persistent, recurrent and transient circulation regimes of the Alborn Sea circulation. The analysis of 936 altimeter-derived weekly absolute dynamic topography (ADT) and surface geostrophic current maps for 1993-2010 reveals the presence of a dominant annual signal and of two interannual modes of variability. The winter-spring phase is characterized by two stable gyral scale features; the well-known Western Anticyclonic Gyre within the western area and the Central Cyclonic Gyre, a new structure not identified in former studies, occupying the central and eastern parts of the Alborn Sea. A double anticyclonic gyre regime constitutes the stable circulation system of the summer-autumn period when the Eastern Anticyclonic Gyre is formed within the eastern Alborn basin. In this case, the Central Cyclonic Gyre is narrower and located closer to the Western Anticyclonic Gyre. They represent two stable states of the system, robust at the decadal time scale, whereas transient changes reflect perturbations on these stable states and are mainly observed at an interannual scale. The circulation variability and the gyral features development may be dynamically linked to the corresponding changes of the Gibraltar transport rates. © 2012. American Geophysical Union. All Rights Reserved.Partial support from EU funded projects MyOcean and PERSEUS is gratefully acknowledgedPeer Reviewe

Ocean color response to wind forcing in the Alboran Sea: A new forecasting method

This work proposes a new method to reconstruct and forecast surface Chlorophyll (Chl) from remotely sensed (SeaWiFS) data in the Alboran Sea, based on the correlation between zonal wind velocities and satellite Chl concentrations. First, the spatial and temporal variability of Chl and zonal wind have been characterized using standard statistics. Second, the annual cycle and trends are removed from the original time series and the residuals submitted to an EOF computation scheme. Then, the correlations between the amplitudes of the first temporal modes of Chl-wind couple have been quantified. Using the most highly correlated pair (Chl-zonal wind, with r. =. 0.63), a simple linear relationship is proposed to reconstruct and forecast the Chl field. This forecasting method is more efficient than persistence for forecast horizons longer than 100. days, with a mean correlation between original and predicted field of 0.73 as compared to 0.5 for persistence for all the year round. In partic\ular, this new method gives a 0.95 mean correlation for periods from 100 to 290. days (while persistence gives 0.5). However, for a constant 8-days prediction horizon the persistence performs marginally better than the proposed method (0.79 vs. 0.68), giving some insight into the temporal scales of the features studied. These results may have significant implications for both short-term operational applications and seasonal forecasts. © 2012 Elsevier B.V.We acknowledge the support of SESAME Integrated Project (Contract number 036949).Peer Reviewe

DUACS DT2021 reprocessed altimetry improves sea level retrieval in the coastal band of the European Seas

More than 29 years of altimeter data have been recently reprocessed by the multi satellite Data Unification and Altimeter Combination System (DUACS) and made available under the name of DT2021 processing through the Copernicus Marine Service (CMEMS) and the Copernicus Climate Change (C3S) Service. New standards have been applied and various geophysical correction parameters were updated compared to the previous release in order to improve the product quality. This paper describes the assessment of this new release through the comparison of both all satellites and two satellites products with external in situ tide gauge measurements in the coastal areas of the European Seas. The aim is to quantify the improvements on the previous DT2018 processing version on the retrieval of sea level in the coastal zone. The results confirmed that the new DT2021 processing version better solves the signal in the coastal band. Moreover, the all satellites dataset provided more accurate sea level measurements when comparing with tide gauges respect to the climatic two satellites dataset due to the better performance of the former for the assessment of higher than climatic frequency signals. On the opposite, we found the two satellite dataset the most suitable product for the assessment of long term sea level time series in the coastal zone due to its larger stability to the detriment of the all satellites dataset.</p

Fueling plankton production by a meandering frontal jet: A case study for the Alboran sea (Western Mediterranean)

Corrección publicada el 26 de diciembre de 2014 con DOI 10.1371/journal.pone.0116653 en relación con la afilicación de uno de los autores© 2014 Oguz et al. A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15-20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.This study is part of the Ocean Forecasting Facility from SOCIB and is also partially supported by Perseus EU funded Project whose support is gratefully acknowledged. JGL acknowledges partial support from the Spanish-funded project CTM2010-21229-C01.Peer Reviewe

Geostrophic and ageostrophic circulation of a shallow anticyclonic eddy off Cape Bojador

European Geosciences Union General Assembly 2014 (EGU2014), 27 april - 2 may 2014, Vienna, Austria.-- 1 pageA shallow mesoscale anticyclonic eddy, observed south of the Canary Islands with satellite altimetry, has been intensively studied with multi-parametric sampling. Hydrographic data from a CTD installed on an undulating Nushuttle platform reveal the presence of a mesoscale anticyclonic eddy of 125 km diameter. The difference in sea level anomaly (SLA) between the interior and the edge of the eddy, as determined from altimetry, is +-15 cm, which compares well with the maximum dynamic height differences as inferred using a very shallow reference level (130 m). Further, the associated surface geostrophic velocities, of about 35 cm/s in the northeast and southwest edges of the eddy, are in good agreement with direct velocity measurements from the ship. Deep rosette-CTD casts (1500 m depth) confirm that the structure is a shallow eddy extending no deeper than 250 m before the fusion with another anticyclone. The SLA-tendency (temporal rate of change of sea surface height) indicates a clear northwestward migration during the two first weeks of November 2008. Applying an eddy SSH based tracker, the eddy¿s velocity propagation is estimated as 4 km/day. Use of the QG-Omega equation diagnoses maximum downward/upward velocities of about +- 2 m/day. The instability of the Canary coastal jet appears to be the mechanism responsible for the generation of the shallow anticyclonic eddyPeer Reviewe

Fueling Plankton Production By a Meandering Frontal Jet: A Case Study For The Alboran Sea (Western Mediterranean)

A three dimensional biophysical model is employed to investigate the biological impacts of a meandering frontal jet for which the Alboran Sea of the Western Mediterranean is considered as a case study. The jet is characterized by relatively low density Atlantic water mass issuing from the Gibraltar Strait within the upper 100 m. It flows eastward as a highly nonlinear meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates an effective phytoplankton growth along the jet. The production intensity is strongest in the western basin and decreases eastwards with the gradual weakening of the jet. The stronger production intensity at the subsurface levels suggests the Alboran Sea is likely more productive than envisaged by the satellite chlorophyll data. The Mediterranean water mass away from the jet as well as the interior of the western and eastern anticyclonic gyres remain poorly productive.JRC.H.1-Water Resource

Computation of a new Mean Dynamic Topography for the Mediterranean Sea from model outputs, altimeter measurements and oceanographic in-situ data

The accurate knowledge of the ocean Mean Dynamic Topography (MDT) is a crucial issue for a number of oceanographic applications and in some areas of the Mediterranean Sea, important limitations have been found pointing to the need of an upgrade. We present a new Mean Dynamic Topography (MDT) that was computed for the Mediterranean Sea. It takes profit of improvements made possible by the use of extended datasets and refined processing. The updated dataset spans the 1993–2012 period and consists of: drifter velocities, altimetry data, hydrological profiles and model data. The methodology is similar to the previous MDT Rio et al. (2007). However, in Rio et al. (2007) no hydrological profiles had been taken into account. This has required the development of dedicated processing. A number of sensitivity studies have been carried out to obtain the most accurate MDT as possible. The main results from these sensitivity studies are the following: moderate impact to the choice of correlation scales but almost negligible sensitivity to the choice of the first guess (model solution). A systematic external validation to independent data has been made to evaluate the performance of the new MDT. Compared to previous version, SMDT-MED-2014 features shorter scales structures, which results in an altimeter velocity variance closer to the observed velocity variance and, at the same time, gives better Taylor skills.The SMDT-MED-2014 was produced in the framework of a contract funded by SOCIBPeer Reviewe