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Hervé Giordani, Guy Caniaux, and Louis Prieur

Abstract

A simplified oceanic model is developed to easily perform cheap and realistic mesoscale simulations on an annual scale. This simplified three-dimensional oceanic model is obtained by degenerating the primitive equations system by prescribing continuously analysis-derived geostrophic currents U g into the momentum equation in substitution of the horizontal pressure gradient. Simplification is provided by a time sequence of U g called guide, which is used as a low-resolution and low-frequency interpolator. This model is thus necessarily coupled to systems providing geostrophic currents—that is, ocean circulation models, analyzed/reanalyzed fields, or climatologies. In this model, the mass and currents fields are constrained to adjust to the geostrophic guide at all scales. The vertical velocity is deduced from the vorticity equation, which ensures the coherence between the vertical motion and the geostrophic structures evolution. Horizontal and vertical advection are the coupling processes that can be activated independently from each other and offer the possibility to (i) continuously derive a three-dimensional model when all processes are activated, (ii) understand how some retroaction loops are generated, and (iii) study development of structures as a function of the geostrophic environment. The model was tested during a 50-day lasting simulation over the Program Océan Multidisciplinaire Méso Echelle (POMME) experiment (northeast Atlantic Ocean, September 2000–October 2001). Optimal analyzed geostrophic currents were derived weekly during POMME from a quasigeostrophic model assimilating altimeter data. Comparison with independent in situ and satellite data indicates that this simulation is very realistic and does not drift, thanks to the prescribed geostrophic guide.

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Gilles Reverdin, Jean-Claude Gascard, Bernard Le Cann, Louis Prieur, Michel Assenbaum, and Pascale Lherminier

Abstract

An anticyclonic mode water vortex and its environment were investigated from November 2000 to September 2001 in the northeast Atlantic (near 43.5°N, 15°–19°W) with neutrally buoyant drifting floats, moored current meters, satellite altimetric sea surface height, and several hydrological surveys and sections. These observations reveal a coherent inner core (∼30 km in diameter) made of very oxygenated northeast Atlantic central waters (11°–12.7°C and 35.5–35.7 on the 1978 practical salinity scale) from 150 m down to about 750-m depth. The core presents high relative vorticity (up to approximately −0.5 times the Coriolis frequency f ) within at least 10 km of its center, near 400–700 m. Peak velocity along the core rim is located deeper than 600 m bordering the deepest and densest (σθ = 27.175 kg m−3) northeast Atlantic mode water found during the Programme Océan Multidisciplinaire Méso Echelle (POMME) project. This water likely originates north of 47°N, where it could have been in contact with the sea surface in early 1999. Below the core, large near-inertial internal waves are found. At least during spring and summer 2001, the core was embedded in a much larger anticyclonic eddy that extends to 100 km from its center, with azimuthal velocity decreasing from the sea surface to 1500 m. This eddy does not trap floats for a long time and is associated with a sea level anomaly on the order of 10 cm. From January through August 2001, both the core and the larger eddy moved anticyclonically around a shallow part of the Azores–Biscay ridge. The core trajectory also exhibits smaller anticyclonic loops on shorter time scales, suggesting that at least at times it is not located at the center of the larger eddy.

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Emanuele Organelli, Hervé Claustre, Annick Bricaud, Catherine Schmechtig, Antoine Poteau, Xiaogang Xing, Louis Prieur, Fabrizio D’Ortenzio, Giorgio Dall’Olmo, and Vincenzo Vellucci

Abstract

An array of Bio-Argo floats equipped with radiometric sensors has been recently deployed in various open ocean areas representative of the diversity of trophic and bio-optical conditions prevailing in the so-called case 1 waters. Around solar noon and almost every day, each float acquires 0–250-m vertical profiles of photosynthetically available radiation and downward irradiance at three wavelengths (380, 412, and 490 nm). Up until now, more than 6500 profiles for each radiometric channel have been acquired. As these radiometric data are collected out of an operator’s control and regardless of meteorological conditions, specific and automatic data processing protocols have to be developed. This paper presents a data quality-control procedure aimed at verifying profile shapes and providing near-real-time data distribution. This procedure is specifically developed to 1) identify main issues of measurements (i.e., dark signal, atmospheric clouds, spikes, and wave-focusing occurrences) and 2) validate the final data with a hierarchy of tests to ensure a scientific utilization. The procedure, adapted to each of the four radiometric channels, is designed to flag each profile in a way compliant with the data management procedure used by the Argo program. Main perturbations in the light field are identified by the new protocols with good performances over the whole dataset. This highlights its potential applicability at the global scale. Finally, the comparison with modeled surface irradiances allows for assessing the accuracy of quality-controlled measured irradiance values and identifying any possible evolution over the float lifetime due to biofouling and instrumental drift.

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