Las características de LIW: un malentendido asombroso

Levantine Intermediate Water (LIW) is a warm salty water formed in one out of four main zones of dense water formation in the Mediterranean Sea. LIW spreads as a density current and first appears on a ϴ-S diagram as a sharp peak that then smoothens out, often leading to the so-called “scorpion-tail” image with a ϴ (S) maximum above (below) the expected core. Both maxima have always been considered, somewhat fuzzily (even by us), as LIW characteristics without having ever been analysed theoretically. We question neither the “scorpion-tail” image nor the “core-method” nor qualitative analyses of either LIW or other waters characterized by similar extrema. But data from the Strait of Gibraltar demonstrate that characterizing and/or delimiting LIW by these maxima gives LIW a much greater importance than it actually merits so all quantitative analyses of LIW musts be reconsidered. Calculations made as simple as possible to simulate a warm salty layer of intermediate water (IW) mixing with waters lying above and below suggest that these maxima i) can be understood only when all three waters are considered together, ii) can evolve in different ways, iii) generally tend to move from the core of the IW layer outwards, and hence iv) can neither characterize nor delimit the IW in any way. Actual simulations with more sophisticated parameterizations are obviously needed. In addition, we suggest that what has to date been called LIW in the western basin in fact represents all intermediate waters formed in all zones of dense water formation in the eastern basin, i.e. not only Levantine waters but also, in particular, Aegean/Cretan waters. To provide a logical counterpart to WIW (Western Intermediate Water), we therefore suggest that, from the Channel of Sicily downstream, LIW should be renamed Eastern Intermediate Water (EIW).El Agua Levantina Intermedia (LIW) es una masa de agua caliente y salada que se forma en el Mediterráneo Oriental. Se esparce como una corriente de densidad y aparece en un diagrama ϴ-S como un pico pronunciado que se va suavizando, produciendo a menudo una imagen de “cola de escorpión” con un máximo de ϴ (S) por encima (por debajo) del nivel esperado de su núcleo. Ambos máximos se han considerado siempre, de forma algo difusa, como características definidoras de LIW sin haber sido analizados nunca teóricamente. No cuestionamos aquí ni la imagen de “cola de escorpión” ni el “método del núcleo” ni los análisis cualitativos de LIW ni de otras masas de agua caracterizadas por extremos similares. Pero datos obtenidos en el Estrecho de Gibraltar demuestran que caracterizar y/o limitar LIW por estos máximos otorga a esta masa de agua una importancia mucho mayor que la que tiene en realidad, con lo cual todos los análisis cuantitativos de LIW hechos hasta ahora deben ser reconsiderados. Cálculos hechos de la forma más simple posible para simular una capa de agua intermedia (IW) caliente y salada mezclándose con las aguas que tiene por encima y por debajo sugieren que estos máximos i) sólo pueden entenderse cuando se consideran las tres aguas conjuntamente, ii) pueden evolucionar de formas distintas, iii) generalmente tienden a desplazarse desde el núcleo de la capa de IW hacia afuera, y en consecuencia iv) no pueden caracterizar ni delimitar a la propia IW de ninguna manera. Obviamente estas conclusiones hay que confirmarlas con simulaciones completas que usen parametrizaciones más sofisticadas. Además sugerimos que lo que hasta ahora se ha llamado LIW en la cuenca occidental, en realidad representa al conjunto de las aguas intermedias formadas en todas las zonas de formación de agua densa de la cuenca oriental, es decir no sólo en la Levantina sino también, y en particular, en la Egea/Cretense. Para tener un equivalente de la WIW (Agua Intermedia Occidental), sugerimos que a partir del Canal de Sicilia, el agua intermedia procedente de la cuenca oriental sea llamada EIW (Agua Intermedia Oriental) en lugar de LIW

Las características de LIW: un malentendido asombroso! (adenda)

Discussions following the publication of “Levantine Intermediate Water characteristics: an astounding general misunderstanding!” (Millot 2013a) confirmed that this warm salty (similar results with cool fresh) intermediate water was generally thought to be characterized, even after significant mixing, by a homogeneous core (i.e. a dσ/dz minimum) while we think it could be characterized by a dσ/dz maximum. Additional computations specify our feelings and suggest that only such a hypothetical dσ/dz maximum can provide information about the characteristics of these intermediate waters, in this case only the local immersion of the core, since the associated s depends essentially on the σ values of all the surrounding waters encountered upstream, while the Θ and S maxima evolve continuously. Because we are convinced that such studies have a global importance and deserve much more interest than they have received up to now, we hope that these additional computations and data analyses will motivate really theoretical studies that could be easily checked with a consequent data set available all over the Mediterranean Sea in particular.Discusiones a partir de la publicación de “Levantine Intermediate Water characteristics: an astounding general misunderstanding!” (Millot 2013a) confirmaron que esta masa de agua intermedia caliente y salada (igualmente válido para un agua fría y dulce) se había considerado siempre caracterizada, incluso tras ser significativamente mezclada, por un núcleo homogéneo (o sea un mínimo de dσ/dz), mientras que nosotros pensamos que podría caracterizarse por un máximo de dσ/dz. Cálculos adicionales especifican esta idea y sugieren que únicamente este hipotético máximo de dσ/dz puede proporcionar información sobre las características de dicha masa de agua, en este caso sólo la profundidad local del núcleo, mientras que la σ asociada depende esencialmente de los valores de σ de todas las aguas arriba circundantes, mientras que los máximos de Θ y S evolucionan continuamente. Dado que estamos convencidos que estos estudios tienen una importancia global y merecen mucho más interés que el recibido hasta ahora, esperamos que estos cálculos adicionales y análisis de datos motivarán estudios teóricos que podrían ser fácilmente verificados con conjuntos de datos disponibles en particular en todo el Mediterráneo

The effect of Mistral wind on the Ligurian current near Provence

International audienceThe effect of the mistral wind on the Ligurian current has been studied using the NOAA 5-VHRR imagery. A frontal zone separates the Ligurian current and colder water upwelled from the Gulf of Lions. It is found that the surface flow associated with the current is halted by strong westerly winds. When the wind drops, the frontal zone moves westward at speeds up to 0.3 m/sec. During a period of stratification, the Ligurian current in the surface layer tends to flow along the coasts of the Gulf of Lions

La circulación superficial en la cuenca oriental del mar Mediterráneo

The schema of the Atlantic Water (AW, 100-200 m thick) circulation in the eastern basin of the Mediterranean Sea elaborated in the 1990s (and widely referred to nowadays) mainly shows jets meandering offshore across the whole basin. However, all previous schemata (since the 1910s) and an analysis of infrared (IR) satellite images in the 1990s show counterclockwise circulation at basin scale. A former controversy about the circulation was elucidated in the western basin where IR images helped describe the mesoscale features and demonstrate their role in the circulation. This motivated the detailed analysis of IR daily and weekly composites (~1000) from 1996 to 2000, and of monthly composites since 1985. We show that AW circulates along the upper part of the continental slope in a counterclockwise direction around the whole basin. In the south and all year long, this circulation is unstable and generates mesoscale anticyclonic eddies that spread AW offshore; in the north dense water formation induces larger seasonal variability. These mesoscale eddies, as well as the Etesian-induced eddies Ierapetra and Pelops, can be followed for years, sometimes several hundreds of km away from where they are formed, and they can merge and/or interact with the alongslope circulation.Los esquemas de circulación del Agua Atlántica (AW, 100-200 m de grosor) en el Mediterráneo oriental elaborados en los años 1990 (y abundantemente citados en la actualidad) presentan principalmente una corriente en chorro ondulante atravesando el centro de la cuenca. Por el contrario, todos los esquemas anteriores (desde los años 1910) y un análisis de imágenes infrarojas (IR) de satélite en los noventa presentan una circulación antihoraria a escala de la cuenca. Una controversia anterior sobre la circulación en la cuenca occidental fue resuelta gracias a que las imágenes IR ayudaron a describir los fenómenos de mesoescala y demostrar su papel en la circulación. Esto motivó un análisis detallado de imágenes IR compuestas diarias y semanales (~1000) durante 1996-2000 y mensuales desde 1985. Aquí demostramos que el AW en general circula sobre la parte superior del talud continental, de forma antihoraria por toda la cuenca. En el sur, y a lo largo de todo el año, esta circulación es inestable y genera remolinos anticiclónicos de mesoescala que esparcen el AW hacia alta mar; en el norte la formación de agua densa induce una gran variabilidad estacional. Estos remolinos de mesoescala, así como los inducidos por los vientos Etesios (Ierapetra y Pelops), pueden ser seguidos durante años, a veces por varios centenares de quilómetros a partir de su lugar de formación, y pueden unirse y/o interaccionar con la circulación a lo largo del talud.

Upwelling in the Gulf of Lions

International audienceThe hydrological and meteorological characteristics of the Gulf of Lions are such that upwelling occurs with no bias due to tides or strong longshore circulation. The sky is generally cloud-free, an uncommon feature in an upwelling area that allows extensive use of satellite infrared data. The observations are adequate to compute mean maps of the sea-surface temperature during upwelling events. Undoubtedly upwelling is much more intense along straitght coastal segments 10 to 20 km long that near capes and small bays; upwelling locations are mainly related to the coastline shape. The imagery also suggests that the surface circulation varies markedly in space and time; this has been verified by in situ measurements, as has the existence of wind-induced eddies in the surface layer. Satellite images from the largest upwelling regions (nothwest Africa, Oregon, Peru) show similar spatial variability of the sea-surface temperature, but because of the rectilinear coastline, and except for some specific areas characterized by highly variable wind stress or bottom topography, plumes and eddies move slightly alongshore and are not characteristic of a mooring point. The geomorphology of the Gulf of Lions is such that eddies have a fixed location and mean currents are significant. Upwelling studies in such areas might be simplified by the reduction of the perturbations associated with the general circulation and geostrophic trubulence

Infrared remote sensing in the Gulf of Lions

International audienceSpatial and temporal variabilities of the upwelling in the Gulf of Lions and some characteristics of the Ligurian current are studied by thermal infrared satellite imagery. Upwelling develops along straight coastal segments of some ten to twenty kilometers in length. On-offshore jets of cool water driven from major upwelling centers and unexpected circulations are clearly detected from space. Off the coasts of Provence, the Ligurian current is halted by strong westerly winds. When the wind drops, the surface layer current flows on to the continental shelf of the Gulf of Lions at speeds up to 30 cm/sec. These results suggest that, during summer at least, the upwelling and the surface-layer circulation mainly depend upon small-and meso-scale features of the coastline

Piezoelectric signal suppression by a composite-pulse sequence in NMR

International audienceNumerous NMR techniques are available for the study of nuclei with spin I ≥ 1. These nuclei interact with their surrounding electric field gradient, which depends on the symmetry of the crystallographic site. Spurious (or piezoelectric) signals, due to the piezoelectric and ferroelectric properties of a LiNbO3 crystal and generated by the vibration of the macroscopic electric dipole of the crystal, have been observed with the one-pulse sequence and cancelled using a composite-pulse sequence. The suppression of these piezoelectric signals by this sequence is illustrated by lithium-7 (I = 3/2) nuclei. Java applets available in our web site www.pascal-man.com for the determination of quadrupole parameters from one-dimensional nutation method are also presented

analyse expérimentale de la réalisation de microcavités sur substrats polymères thermoplastiques par le procédé de roll embossing

de nouveaux developpements experimentaux ont ete realises afin de mettre au point le procede de roll embossing pour la realisation de microstructure en continu pour des polymeres et des polymeres charges. des caracterisations rheologiques ont ete realisees pour optimiser les parametres procedes. les resultats obtenus par MMB conduisent a l'obtention de composants sans defauts. des comparaisons geometriques et topographiques entre les repliques et les empreintes du moule montrent un bon remplissage des composants au dela de 200°