Three-Dimensional Characterization of a Coastal Mode-Water Eddy from Multiplatform Observations and a Data Reconstruction Method

Coastal mesoscale eddies are important oceanic structures partially responsible for regulating ocean-shelf exchanges. However, their description and characterization are challenging; observations are often too scarce for studying their physical properties and environmental impacts at the required spatio-temporal resolution. Therefore, models and data extrapolation methods are key tools for this purpose. Observations from high-frequency radar, one satellite and two gliders, are used here to better characterize the three-dimensional structure of a coastal mode-water eddy from a multiplatform approach in the southeastern Bay of Biscay in spring 2018. After the joint analysis of the observations, a three-dimensional data reconstruction method is applied to reconstruct the eddy current velocity field and estimate the associated water volume transport. The target eddy is detected by surface observations (high-frequency radar and satellite) for two weeks and presents similar dimensions and lifetimes as other eddies studied previously in the same location. However, this is the first time that the water column properties are also observed for this region, which depicts a mode-water eddy behavior, i.e., an uplift of the isopycnals in the near-surface and a downlift deeper in the water column. The reconstructed upper water column (1–100 m) eddy dynamics agree with the geostrophic dynamics observed by one of the gliders and result in cross-shelf inshore (offshore) volume transports between 0.04 (−0.01) and 0.15 (−0.11) Sv. The multiplatform data approach and the data reconstruction method are here highlighted as useful tools to characterize and three-dimensionally reconstruct coastal mesoscale processes in coastal areas.En prensa0,64

Ikusezintasunerantz: eremu elektromagnetikoen kontrola metamaterialen bidez

Historian zehar, greziar mitologiatik gaur egun arte , gizakiak ikusezin izatearekin amestu du. Hala ere, duela urte gutxi arte ez da benet an zientifikoki azaldu nola gauzatu amets hori . Tachi - ren lanetik [1 ] hasita , non transparentzia birtual bat lortzen den, metamaterialen mundura pasatzen da argi - izpiak nahi eran d esbideratuz eta modu honetan ikusezintasun a lortuz. Metamaterialak artifizialki sortutako mate rialak dira, laborategietan dis einatuak eta guk behar ditugun propietateez esleitu ak . Hau en bidez , ingurune baten permitibitate elektrikoa eta iragazkortasun magnetikoa , eta ondorioz handik pasatzen diren uhin elektromagnetikoak kontrolatzea lortzen da. Horrela, argiaren desbiderapen kontrolatua lortu nahi da , eta fenomeno hori deskribatzen duen formalismoari transformazioaren optik a deritzo . Honi esker, esater ako, ikusezintasun - estalki esferiko batek, modu teoriko batean nola funtzionatu ko lukeen kalkulatu eta simula daiteke. Hala ere, ikusezintasunaren zientzia k hasi besterik ez du egin eta oraindik lan handia dago egiteko arlo honen inguruan, oraindik ez b aita begi bistaz antzematen d en objektu rik iku sezin bihurt

Observational challenges for studying coastal eddies: an application case in the Bay of Biscay

Atlantic form Space Workshop, 23-25 January 2019, Southampton, UK.-- 16 pagesRecent work has demonstrated the recurrent presence of coastal eddies (diameter about 50 km) in the area covered by a land-based HF radar (HFR) in the SE Bay of Biscay. These eddies can persist during several weeks and play a significant role in the export of coastal rich waters towards the open ocean. The study of their surface properties at high temporal and spatial resolution is possible thanks to the continuous monitoring of surface currents within the HFR footprint area. Their observation using satellite measurements is also possible, although limited by the discontinuous coverage and resolution of the data. These rapidly evolving eddies can be detected by the altimetry; nevertheless, the low spatio-temporal resolution of the data does not always enable to map accurately the associated surface geostrophic currents. In the periods of low cloud coverage, visible and satellite IR data offer further possibilities, when combined with an appropriate theoretical framework as: the use of sequences of images to retrieve the velocity field that originated the motion of the observed tracers, or the use single SST maps to derive high-resolution surface currents using an approach based in the Surface Qua geostrophic (SQG) approximation. Lower-resolution but more repetitive maps can be constructed using microwave remote sensing data, as AMSRE SST or L-band SSS, that are not affected by the presence of clouds. Within the framework of SQG it is possible to retrieve the three-dimensional dynamics of the eddy, if environmental and dynamical conditions are the appropriate.These eddies could be more frequent than commonly thought, and thus may play a very significant role in the transport of water masses in the Atlantic. But in the absence of an extensive network of HFRs along the basin coast, this idea is speculative. The use of remote sensing maps to extract dynamic information about these coastal processes could help filling this gap. In this work, we investigate the range of application of SQG to solve and describe coastal eddies, comparing with measurements from the SE Bay of Biscay HFR and we discuss the prospect of extending this approach to the whole Atlantic coastal ar

Coastal submesoscale processes and their effect on phytoplankton distribution in the southeastern Bay of Biscay

Submesoscale processes have a determinant role in the dynamics of oceans by transporting momentum, heat, mass, and particles. Furthermore, they can define niches where different phytoplankton species flourish and accumulate not only by nutrient provisioning but also by modifying the water column structure or active gathering through advection. In coastal areas, however, submesoscale oceanic processes act together with coastal ones, and their effect on phytoplankton distribution is not straightforward. The present study brings the relevance of hydrodynamic variables, such as vorticity, into consideration in the study of phytoplankton distribution, via the analysis of in situ and remote multidisciplinary data. In situ data were obtained during the ETOILE oceanographic cruise, which surveyed the Capbreton Canyon area in the southeastern part of the Bay of Biscay in early August 2017. The main objective of this cruise was to describe the link between the occurrence and distribution of phytoplankton spectral groups and mesoscale to submesoscale ocean processes. In situ discrete hydrographic measurements and multi-spectral chlorophyll a (chl a) fluorescence profiles were obtained in selected stations, while temperature, conductivity, and in vivo chl a fluorescence were also continuously recorded at the surface. On top of these data, remote sensing data available for this area, such as high-frequency radar and satellite data, were also processed and analysed. From the joint analysis of these observations, we discuss the relative importance and effects of several environmental factors on phytoplankton spectral group distribution above and below the pycnocline and at the deep chlorophyll maximum (DCM) by performing a set of generalized additive models (GAMs). Overall, salinity is the most important parameter modulating not only total chl a but also the contribution of the two dominant spectral groups of phytoplankton, brown and green algae groups. However, at the DCM, among the measured variables, vorticity is the main modulating environmental factor for phytoplankton distribution and explains 19.30 % of the variance. Since the observed distribution of chl a within the DCM cannot be statistically explained without the vorticity, this research sheds light on the impact of the dynamic variables in the distribution of spectral groups at high spatial resolution

Integration of HF Radar Observations for an Enhanced Coastal Mean Dynamic Topography

International audienc

Synthesis of satellite validation results

This report presents the results of Task 4.4: Improving the use of in situ observations for the long-term validation of satellite observation

Copernicus Marine Service Ocean State Report, Issue 3 Introduction

International audienc