Tilted convective plumes in numerical experiments

International audienceThe dynamics of a single convective plume in an isothermal ocean is investigated by numerically inte- grating the three dimensional Boussinesq equations. Our study emphasizes on the important consequences of a non-vanishing angle between the axis of rotation and the buoyancy force (gravity). Experiments are performed for four different values of the angle corresponding to open-ocean convection at latitude: 90° N, 60° N, 45° N and 0° N. We show that the horizontal component of the rotation vector leads to qualitative and quantitative changes in the convective dynamics of a single plume. Plume structures are aligned along the axis of rota- tion rather than the direction of gravity (tilted convection), the vertical velocity of the plume is reduced, and the mixing is enhanced by the horizontal component of the rotation vector. These results suggest that in future parametrisations of ocean convection the effect of the horizontal component of the rotation vector should be included

ASSESSING THE REALISM OF OCEAN SIMULATIONS AGAINST HYDROGRAPHY AND ALTIMETRY

Future climate prediction systems will include ocean models at eddy-admitting to eddy-resolving resolution, i.e. ° on the horizontal or finer. The development and calibration of such models requires the us

Mode waters and subduction rates in a high-resolution South Atlantic simulation

Water mass production and destruction in the subtropical South Atlantic gyre is studied. A high resolution numerical model is used to examine regional mode water formation and estimate the associated instantaneous and mean subduction rates. Primitive equation dynamics expressed in depth following (sigma) coordinates are employed. The main hydrographic and kinematic features of the South Atlantic are faithfully reproduced by the model. In particular, the principle current systems appear and the model exhibits a sequence of ventilated potential vorticity minima on density surfaces coinciding with those of observed South Atlantic mode waters. The formation sequence within the model of these mode waters is described. Net formation rates are estimated using a pseudo-Lagrangian method and by diagnosing the time history of subsurface water mass volumes. Maximum formation rates occur in the density bands of the mode waters. It is argued that the roots of the model mode waters are found along open ocean late winter outcrops, rather than in the waters entering the gyre from the Brazil Current/Malvinas Current Confluence region. Eddies generate interannual variability in mode water formation and precondition the waters in the outcrop regions for convection. On the other hand, the eddy kinetic energy of the Confluence region is too intense to permit a direct connection between deep convection cells in the western boundary current and those in the open South Atlantic that directly form mode water

Sea ice inertial oscillations in the Arctic Basin

International audienceAn original method to quantify the amplitude of inertial motion of oceanic and ice drifters, through the introduction of a non-dimensional parameter M defined from a spectral analysis, is presented. A strong seasonal dependence of the magnitude of sea ice inertial oscillations is revealed, in agreement with the corresponding annual cycles of sea ice extent, concentration, thickness, advection velocity, and deformation rates. The spatial pattern of the magnitude of the sea ice inertial oscillations over the Arctic Basin is also in agreement with the sea ice thickness and concentration patterns. This argues for a strong interaction between the magnitude of inertial motion on one hand, the dissipation of energy through mechanical processes, and the cohesiveness of the cover on the other hand. Finally, a significant multi-annual evolution towards greater magnitudes of inertial oscillations in recent years, in both summer and winter, is reported, thus concomitant with reduced sea ice thickness, concentration and spatial extent

Intrinsic variability of the Atlantic Meridional Overturning Circulation at interannual-to-multidecadal time scales

The low-frequency variability of the Atlantic meridional overturning circulation (AMOC) is investigated from 2, ¼°, and ° global ocean–sea ice simulations, with a specific focus on its internally generated (i.e., “intrinsic”) component. A 327-yr climatological ¼° simulation, driven by a repeated seasonal cycle (i.e., a forcing devoid of interannual time scales), is shown to spontaneously generate a significant fraction R of the interannual-to-decadal AMOC variance obtained in a 50-yr “fully forced” hindcast (with reanalyzed atmospheric forcing including interannual time scales). This intrinsic variance fraction R slightly depends on whether AMOCs are computed in geopotential or density coordinates, and on the period considered in the climatological simulation, but the following features are quite robust when mesoscale eddies are simulated (at both ¼° and ° resolutions); R barely exceeds 5%–10% in the subpolar gyre but reaches 30%–50% at 34°S, up to 20%–40% near 25°N, and 40%–60% near the Gulf Stream. About 25% of the meridional heat transport interannual variability is attributed to intrinsic processes at 34°S and near the Gulf Stream. Fourier and wavelet spectra, built from the 327-yr ¼° climatological simulation, further indicate that spectral peaks of intrinsic AMOC variability (i) are found at specific frequencies ranging from interannual to multidecadal, (ii) often extend over the whole meridional scale of gyres, (iii) stochastically change throughout these 327 yr, and (iv) sometimes match the spectral peaks found in the fully forced hindcast in the North Atlantic. Intrinsic AMOC variability is also detected at multidecadal time scales, with a marked meridional coherence between 35°S and 25°N (15–30 yr periods) and throughout the whole basin (50–90-yr periods)

Análisis multiparamétrico y validación de tres simulaciones globales en el Mediterráneo occidental

We analyse a hierarchy of three 1/4° global numerical simulations (ORCA-025.G70 (G70), ORCA-025.G85 (G85) and GLORYS1V1 (GLORYS)) by assessing their performance against observational data in the western Mediterranean. When compared with the EN3_v2a temperature and salinity database, the simulations are capable of reproducing surface layer temperature interannual variability but G70 is inaccurate with intermediate and deep-layer trends. This aspect is improved by the increased vertical resolution of G85 and by data assimilation in GLORYS. Salinity is the most problematic parameter because of the imbalance of the freshwater budget derived from inaccuracies in the atmospheric forcing parameters. Surface salinity restoring is needed in order to avoid salinity drift and inaccurate sea-level trends. G70, with a stronger relaxation, has a lower trend closer to altimetric measurements than G85. Mean surface circulation is well reproduced for relatively large-scale signals. We further show that G85 and GLORYS provide evidence of the 2004-2005 and 2005-2006 deep convection events in the Gulf of Lion. Finally, transports through the main straits of the western Mediterranean are correct in order of magnitude, direction and seasonal cycle when compared with observations. This study contributes to the improvement of the ORCA hierarchy of simulations and points out the strengths and weaknesses of these simulations in the Mediterranean Sea.Analizamos un conjunto de tres simulaciones numéricas globales de 1/4º (ORCA-025.G70 (G70), ORCA-025.G85 (G85) y GLORYS1V1 (GLORYS)) comparándolas con datos observacionales en el Mediterráneo Occidental (WMED). Contrastando con la base de datos de temperatura y salinidad EN3_v2a las simulaciones son capaces de reproducir la variabilidad superficial en temperatura sin embargo G70 exagera las tendencias en capas intermedias y profundas. Este aspecto es mejorado por la mayor resolución vertical de G85 y la asimilación de datos de GLORYS. La salinidad es el parámetro más problemático debido al desequilibrio del balance de agua dulce procedente de imprecisiones en los parámetros de forzamiento atmosférico. Relajación de salinidad superficial es necesaria para evitar derivas de salinidad y nivel del mar. De hecho G70 con su relajación más intensa tiene una tendencia más baja (y más cercana a mediciones altimétricas) que G85. La circulación promedio en superficie está bien reproducida para señales relativamente grandes. Además, demostramos que G85 y GLORYS muestran evidencia de los eventos de convección profunda de 2004-2005 y 2005-2006 en el Golfo de León. Finalmente, transportes a través de los principales canales y estrechos del Mediterráneo Occidental son correctos cuando se comparan con observaciones, tanto en orden de magnitud y dirección, como en el ciclo estacional. Este estudio contribuye a la mejora del conjunto de simulaciones ORCA y señala las fortalezas y debilidades de estas simulaciones en el Mar Mediterráneo

Stochastic variability of oceanic flows above topography anomalies

International audienceWe describe a stochastic variability mechanism which is genuinely internal to the ocean, i.e. not due to fluctuations in atmospheric forcing. % The key ingredient is the existence of closed contours of bottom topography surrounded by a stirring region of enhanced eddy activity. This configuration leads to the formation of a robust but highly variable vortex above the topography anomaly. The vortex dynamics integrates the white noise forcing of oceanic eddies into a red noise signal for the large scale volume transport of the vortex. The strong interannual fluctuations of the transport of the Zapiola anticyclone ($\sim 100 \ Sv$) in the Argentine basin are argued to be partly due to such eddy-driven stochastic variability, on the basis of a $310$ years long simulation of a comprehensive global ocean model run driven by a repeated-year forcing

PROPHYLACTIC EVALUATION OF SHOULDER PROPRIOCEPTION IN ELITE SWIMMERS

It is suggested that poor shoulder proprioception contributes to shoulder pain in swimmers. However, there is a lack of studies describing the measurement method for shoulder proprioception. The purposes of this preliminary study was to investigate the scapular position depending on arm scaption as a first step in the development of a measurement method for three-dimensional shoulder proprioception. An asymptomatic young adults participated in this study. His scapular rotation were measured as a function of arm position during scaption in two consecutive days. The results showed that scapular rotations are not a reproducible function of humerus elevation. Those findings suggested that the assessement of shoulder proprioception should rely on the evaluation of both gleno-humeral and scapulo-thoracic joints to be valid

Transfer of particulate matter from the Northwestern Mediterranean continental margin: Variability and controlling factors

International audienceLong-term observations of monthly downward particle fluxes and hourly currents and temperaturewere initiated in 1993 in two canyons of the continental margin of the Gulf of Lion. The goals of thissurvey were to estimate its contribution to the CO 2 global budget and to understand the role offorcing factors in the control of present-day particle exchange across this margin. A previousstatistical analysis of the long-term time series suggested that variability in the transfer of particulatematter to the deep ocean could be the result of the effect of the meandering of the Northern Currentand by dense water formation in winter rather than variations in the sources of matter. Numericalsimulations have been carried out to consider these hypotheses. A model is used to examine theimpact of local atmospheric forcing (wind stress, heat fluxes, precipitation–evaporation budget) onthe variability of the oceanic circulation and of mass fluxes within the canyons from December toApril, for five consecutive years between 1996 and 2001. Results show an east-west gradient of massexport on the shelf and a positive correlation between anomalies of dense water formation rates andinterannual variability of particle fluxes. However, in the eastern part of the Gulf, the simulated massexport from the shelf is not significant, even during a winter of strong convection, when the measuredparticle fluxes are at maxima. Moreover, although the model suggests that the dense water formationcould be the major hydrodynamic forcing factor, this process is not sufficient to completely explainthe space and time variations of observed particle fluxes, especially at depth