8:35 - 8:55
Coastal Mesoscale Structures at the Entrance to the Gulf of California
Center of Investigation and Education Superior of Ensenada, Mexico
The Cabo Pulmo National Park is the northernmost coral reef community of the Mexican Pacific. It is located on the gulf coast of the Baja California Peninsula, approximately at 23.5 ° N, in a privileged position to study the coastal dynamics of the entrance to the Gulf of California. We study various mesoscale phenomena that interact with the coast and modulate the coastal circulation. In this work we focus on the physical mechanisms capable of enhancing the productivity of a subtropical coastal ocean. We use sea surface temperature maps from GHRSST, chlorophyll maps from MODIS and COPERNICUS to document and describe offshore filaments that generate cross-shelf transport and export significant amounts of mass, momentum and nutrients (and presumably net productivity). Sea level coastal altimetry from the Adaptive Leading-Edge Subwaveform retracking procedure, and for JASON-2 and Envisat, is used to estimate coastal currents for some of these filaments. The coastal altimetry estimates are validated using a 7-year time-series of in situ currents in the Cabo Pulmo National Park. We present case studies of different types of filaments and an analysis of their evolution and of their contribution to the coastal productivity.
8:55 - 9:15
Satellite Altimetry in the Continental Shelf of the Southwestern Atlantic, Argentina
1Centro de Investigaciones del Mar y la Atmósfera (CIMA/CONICET-UBA), Ciudad Autónoma de Buenos Aires, Argentina; 2Departamento de Ciencias de la Atmósfera y los Océanos (DCAO/FCEN-UBA), Ciudad Autónoma de Buenos Aires, Argentina; 3UMI-IFAECI CNRS-CONICET-UBA, Ciudad Autónoma de Buenos Aires, Argentina; 4Laboratoire d'Océanographie Dynamique et de Climatologie (LOCEAN), Université Pierre et Marie Curie, Paris, France; 5Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Mar del Plata, Argentina
This study shows preliminary results of the data obtained along the northern transect of the Franco-Argentinean CASSIS (Southwest Atlantic Currents Satellite In-Situ) project. Between December 2014 and November 2015, five moorings recorded direction and speed of currents, temperature, salinity and pressure. The five moorings were deployed under the Jason track #26: two in the continental shelf (A1 and A2) and three in the shelf-break (A4, M1 and M2). Correlation with satellite altimetry data is statistically significant within all the moorings, being significantly larger over the shelf-break than over the continental shelf. Here we focus on the results obtained from A1 and A2, trying to understand the reason of the lower performance of the altimetry data over the continental shelf than over the shelf-break. A preliminary analysis suggest that the ageostrophic component imposed by the dominant NNW winds is likely to be responsible of the lowest correlation found between the meridional components over the shelf. Coastal altimetry products (CTOH, ALES), new products from CLS with 1/8 of degree spatial resolution and that include Ekman currents, numerical model outputs and other satellite data (SAR, SST, ocean colour) are being analysed. Geophysical corrections are also examined.
9:15 - 9:35
Performance of Different Altimetry-Derived Products and Techniques for Manifesting Mesoscale Eddies in Coastal Areas
University of Liege, Belgium
Altimetry-derived data open wide opportunities for assessing global and mesoscale circulation of the World Ocean through an inspection of the gridded fields of sea level anomaly (SLA). Nevertheless, for small marine basins there exist some discrepancies in mesoscale eddy statistics provided by the analysis of SLA, on one side, and direct observations of eddies in satellite imagery, on the other side. Thus, satellite imagery usually reveal that cyclonic and anticyclonic eddies are having different dynamical and morphological properties, while on analysis of SLA such differences are not well represented.
The aim of the present study is to compare the performance of the different altimetry datasets (e.g. provided by the CMEMS and Legos) as well as of different eddy detection techniques such as a geometrical method and some variations of a closed-contour approach based on analysis of the SLA, relative vorticity, Okubo-Weiss parameter, etc. As a region of interest, the Western Mediterranean Basin is being used, due to its intensive mesoscale eddy activity. The time coverage is from 2011 to 2013. As a ‘ground truth’, sea surface temperature (SST) fields are being used, a visual analysis of which allowed to detect more than 2200 eddies with diameters in the range 30-160 km.
Preliminary results of application of the closed-contour approach allowed to suppose that only anticyclonic eddies with a diameter exceeding 70 km could be sustainably represented by closed contours in the fields of SLA and relative vorticity. Cyclonic eddies, due to their smaller spatial scale and non-geostrophic nature, could not be resolved by the fields of SLA.
This research was supported by the University of Liege and the EU in the context of the FP7-PEOPLE-COFUND-BeIPD project.
Poleward Currents from Coastal Altimetry: The West Coast of Southern Baja California, Mexico
The west coast of Southern Baja California is subject to intense seasonal variability. Lowest temperatures occur from February to April partly due to the upwelling but also to cold water advection associated to the California Current. From July to October, the advance of a coastal poleward current carries warm water from the south and is responsible for the coastal seasonal temperature maxima. Analysis of twenty years of coastal altimetry data, 20 to 40 km from the coast, reveal a persistent seasonal equatorward/poleward flow during winter/summer months. We use a time series of currents from moored Acoustic Doppler Profiler (ADP) to validate coastal altimetry data from CTOH/X-TRACK (track 169), in order to study seasonal and interannual coastal current variability. During winter the flow is mainly towards the equator. Speeds obtained from altimetry between February-April reach maxima of 0.4 ms-1 while the ADP recorded maxima around 0.6 ms-1. The poleward flow advances against the climatological wind in a narrow coastal band about 100 km wide, occupying the surface to 80 m depth and with speeds between 0.2 and 0.3 ms-1 in the coastal altimetry, compared to 0.6 ms-1 in the ADP record.
Coastal Altimetry in Support to Marine Observatory and Marine Observatory in Support to Coastal Altimetry: Multi-Platform Validations of Altimetry for Monitoring the Variability of Coastal Fronts
1ESA / RHEA, Italy; 2SERCO, Italy; 3University Of Porto, Portugal; 4ESA / SERCO, Italy; 5MIO, France; 6ESA, Italy
The space-time variability of coastal slope currents plays a key role on the across-shore transport of natural and anthropogenic elements. It is therefore of critical importance to monitor the variations of their front position and intensity, in particular along densely populated coasts such as the littoral zone of the Mediterranean Sea. Our paper proposes to address this issue by giving an overview of integrated multi-sensor approaches aiming at monitoring the multi-scale variability of the Mediterranean Northern Current. Beside this scientific objective, our purpose is also to refine validation approaches for coastal altimetry, by analyzing the potential sources of disagreement between Coastal Altimetry and the Fiducial Reference Measurements (e.g. measurement/correction errors, physical content inhomogeneity, non exact collocations). To achieve this goal, several altimetric datasets and multi-platform observations from oceanographic campaigns and Marine Observatories are analyzed in conjunction with a regional circulation model. This R&D initiative, supported by ESA, is firstly based on an original exploitation of conventional pulse-limited altimetry data. The main outcomes should pave the way for designing validation approaches to assess/optimize improved geophysical corrections and processing algorithms dedicated to future missions whose the on-board technology will more suitable for coastal applications (e.g. Sentinel-6, SWOT).
REVISED ABSTRACT submitted 28/11 after query by OrgComm:
The space-time variability of coastal slope currents plays a key role on the across-shore transport of natural and anthropogenic elements. It is therefore of critical importance to monitor the variations of their front position and intensity, in particular along densely populated coasts such as the littoral zone of the Mediterranean Sea. Our paper proposes to address this issue by presenting the first outcomes of an integrated multi-sensor approach aiming at monitoring the multi-scale variability of the Mediterranean Northern Current. The paper focuses on the scientific exploitation and validations of multi-mission coastal altimetry, by analysing the potential synergies and sources of disagreement with respect to in situ observations; especially regarding measurement errors, physical content inhomogeneity, synopticity issues and the non exact collocations between the different observing systems. To achieve this goal, several altimetric datasets (XTRACK, PEACHI, AVISO) and complementary in situ measurements (e.g. Moving Vessel Profilers, Gliders, CTD, ADCP, HF radar) from Marine Observatories (JULIO, MOOSE) and an oceanographic campaign (OSCAHR) are post-processed and analysed in conjunction with a 10-year regional simulation (SYMPHONIE). This R&D initiative, supported and funded by ESA, is firstly based on the original analysis and validation of pulse-limited Ka and Ku –band coastal altimetry data. The obtained outcomes are promising and pave the way for new multi-sensor approaches aiming at better characterising the coastal ocean dynamics hidden behind small-scale altimetric signals. Indeed, the thorough knowledge of local oceanographic processes appears to be THE key component in order to properly validate and continuously improve geophysical corrections and innovative coastal processing algorithms dedicated to past, new and future high-resolution altimetric missions.