On the early stages of wind-wave generation under accelerated wind conditions

International audienceWhen wind starts to blow, a momentum transfer initiates through the air-water interface generating ocean wave. This transfer is usually characterized in terms of the drag coefficient, CD, but its dependency with wind speed still presents remarkable scatter in the experimental studies. Besides, Babanin and Makin (2008) found that gustiness were responsible to the most distant outliers in drag coefficient values. Also, several studies showed the influence of the sea state and wave age in the roughness and drag coefficient behavior (Smith et al. 1992; Donelan et al. 1993; Drennan 2003). Most of the past studies of wind-waves generation considered uniform and stationary wind speeds. However, in open field it is common to have conditions of wind blowing with a certain acceleration before the constant wind condition is reached. In order to study the early stages of the generation of waves under accelerated wind conditions, a total of five experiments with a characteristic wind speed acceleration were conducted in a large wind-wave facility at the Institut Pytheas (Marseille-France). Momentum fluxes were estimated from hot wire anemometry and, the free surface displacement was measured along the channel tank by resistance and capacitance wire probes. High resolution wind speed and water elevation measurements were acquired at a high resolution rate. During experiments the wind speed was increased with a constant acceleration over time, reaching a constant maximum intensity of 13 m/s. It was observed that during accelerated wind conditions, drag coefficient values depends on the degree of development of the flow regime in the air section and on wave field generation and evolution. The acceleration of wind speed has a direct influence on water surface roughness and water wave evolution in time and in space

Values and physical activity among sports science students in France and China: a transcultural analysis

Objective: The aim of this study was to analyze the relationships between values and physical activity in France (a Western European individualistic country) and in China (an East Asian collectivist country). Method: Six hundred and twenty-seven sport science students in France (N = 308, Mage = 18.99, SD = 1.64) and China (N = 319, Mage = 20.44, SD = 1.09) completed the International Physical Activity Questionnaire long version and the Portrait Values Questionnaire. Results: In both France and China, moderated regression analysis revealed that hedonism positively/negatively predicted physical activity, while security-societal, security-personal, and conformity-rules values negatively predicted physical activity. In contrast, stimulation and universalism-nature values positively predicted physical activity only in France. In China, benevolence and benevolence-care positively predicted physical activity, while power dominance negatively predicted physical activity. Additionally, we found evidence of measurement invariance of the value questionnaire. Discussion and conclusion: Our findings add to the literature by showing that the value–behavior link is partly the same across countries and partly different. Further, our findings show that for certain populations, the previously established hierarchy of human values does not replicate

Observation and estimation of Lagrangian, Stokes and Eulerian currents induced by wind and waves at the sea surface

The surface current response to winds is analyzed in a two-year time series of a 12 MHz (HF) Wellen Radar (WERA) off the West coast of France. The measured currents, with tides filtered out, are of the order of 1.0 to 1.8% of the wind speed, in a direction 10 to 40 degrees to the right of the wind. This Lagrangian current can be decomposed as the vector sum of a quasi-Eulerian current U_E, representative of the top 1 m of the water column, and a part of the wave-induced Stokes drift Uss at the sea surface. Here Uss is estimated with an accurate numerical wave model, thanks to a novel parameterization of wave dissipation processes. Using both observed and modelled wave spectra, Uss is found to be very well approximated by a simple function of the wind speed and significant wave height, generally increasing quadratically with the wind speed. Focusing on a site located 100 km from the mainland, the estimated contribution of Uss to the radar measurement has a magnitude of 0.6 to 1.3% of the wind speed, in the wind direction, a fraction that increases with wind speed. The difference U_E of Lagrangian and Stokes contributions is found to be of the order of 0.4 to 0.8% of the wind speed, and 45 to 70 degrees to the right of the wind. This elatively weak quasi-Eulerian current with a large deflection angle is interpreted as evidence of strong near-surface mixing, likely related to breaking waves.Comment: Submitted to J. Phys. Oceanogr. le 16/10/2008. Revised 18/02/2009, Accepted 03/04/201

Global Observations of Fine-Scale Ocean Surface Topography With the Surface Water and Ocean Topography (SWOT) Mission

The future international Surface Water and Ocean Topography (SWOT) Mission, planned for launch in 2021, will make high-resolution 2D observations of sea-surface height using SAR radar interferometric techniques. SWOT will map the global and coastal oceans up to 77.6 latitude every 21 days over a swath of 120 km (20 km nadir gap). Today’s 2D mapped altimeter data can resolve ocean scales of 150 km wavelength whereas the SWOT measurement will extend our 2D observations down to 15–30 km, depending on sea state. SWOT will offer new opportunities to observe the oceanic dynamic processes at scales that are important in the generation and dissipation of kinetic energy in the ocean, and that facilitate the exchange of energy between the ocean interior and the upper layer. The active vertical exchanges linked to these scales have impacts on the local and global budgets of heat and carbon, and on nutrients for biogeochemical cycles. This review paper highlights the issues being addressed by the SWOT science community to understand SWOT’s very precise sea surface height (SSH)/surface pressure observations, and it explores how SWOT data will be combined with other satellite and in situ data and models to better understand the upper ocean 4D circulation (x, y, z, t) over the next decade. SWOT will provide unprecedented 2D ocean SSH observations down to 15–30 km in wavelength, which encompasses the scales of “balanced” geostrophic eddy motions, high-frequency internal tides and internal waves. Frontiers in Marine Science | www.frontiersin.org 1 May 2019 | Volume 6 | Article 232 Morrow et al. SWOT Fine-Scale Global Ocean Topography This presents both a challenge in reconstructing the 4D upper ocean circulation, or in the assimilation of SSH in models, but also an opportunity to have global observations of the 2D structure of these phenomena, and to learn more about their interactions. At these small scales, ocean dynamics evolve rapidly, and combining SWOT 2D SSH data with other satellite or in situ data with different space-time coverage is also a challenge. SWOT’s new technology will be a forerunner for the future altimetric observing system, and so advancing on these issues today will pave the way for our future

Genome analysis of the necrotrophic fungal pathogens Sclerotinia sclerotiorum and Botrytis cinerea

Sclerotinia sclerotiorum and Botrytis cinerea are closely related necrotrophic plant pathogenic fungi notable for their wide host ranges and environmental persistence. These attributes have made these species models for understanding the complexity of necrotrophic, broad host-range pathogenicity. Despite their similarities, the two species differ in mating behaviour and the ability to produce asexual spores. We have sequenced the genomes of one strain of S. sclerotiorum and two strains of B. cinerea. The comparative analysis of these genomes relative to one another and to other sequenced fungal genomes is provided here. Their 38–39 Mb genomes include 11,860–14,270 predicted genes, which share 83% amino acid identity on average between the two species. We have mapped the S. sclerotiorum assembly to 16 chromosomes and found large-scale co-linearity with the B. cinerea genomes. Seven percent of the S. sclerotiorum genome comprises transposable elements compared t

Drift and mixing under the ocean surface : a coherent one-dimensional description with application to unstratified conditions

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C03016, doi:10.1029/2005JC003004.Waves have many effects on near-surface dynamics: Breaking waves enhance mixing, waves are associated with a Lagrangian mean drift (the Stokes drift), waves act on the mean flow by creating Langmuir circulations and a return flow opposite to the Stokes drift, and, last but not least, waves modify the atmospheric surface roughness. A realistic ocean model is proposed to embrace all these aspects, focusing on near-surface mixing and surface drift associated with the wind and generated waves. The model is based on the generalized Lagrangian mean that separates the momentum into a wave pseudomomentum and a quasi-Eulerian momentum. A wave spectrum with a reasonably high frequency range is used to compute the Stokes drift. A turbulent closure scheme based on a single evolution equation for the turbulent kinetic energy includes the mixing due to breaking wave effects and wave-turbulence interactions. The roughness length of the closure scheme is adjusted using observations of turbulent kinetic energy near the surface. The model is applied to unstratified and horizontally uniform conditions, showing good agreement with observations of strongly mixed quasi-Eulerian currents near the surface when waves are developed. Model results suggest that a strong surface shear persists in the drift current because of the Stokes drift contribution. In the present model the surface drift only reaches 1.5% of the wind speed. It is argued that stratification and the properties of drifting objects may lead to a supplementary drift as large as 1% of the wind speed

Genomic Analysis of the Necrotrophic Fungal Pathogens Sclerotinia sclerotiorum and Botrytis cinerea

Sclerotinia sclerotiorum and Botrytis cinerea are closely related necrotrophic plant pathogenic fungi notable for their wide host ranges and environmental persistence. These attributes have made these species models for understanding the complexity of necrotrophic, broad host-range pathogenicity. Despite their similarities, the two species differ in mating behaviour and the ability to produce asexual spores. We have sequenced the genomes of one strain of S. sclerotiorum and two strains of B. cinerea. The comparative analysis of these genomes relative to one another and to other sequenced fungal genomes is provided here. Their 38–39 Mb genomes include 11,860–14,270 predicted genes, which share 83% amino acid identity on average between the two species. We have mapped the S. sclerotiorum assembly to 16 chromosomes and found large-scale co-linearity with the B. cinerea genomes. Seven percent of the S. sclerotiorum genome comprises transposable elements compared to <1% of B. cinerea. The arsenal of genes associated with necrotrophic processes is similar between the species, including genes involved in plant cell wall degradation and oxalic acid production. Analysis of secondary metabolism gene clusters revealed an expansion in number and diversity of B. cinerea–specific secondary metabolites relative to S. sclerotiorum. The potential diversity in secondary metabolism might be involved in adaptation to specific ecological niches. Comparative genome analysis revealed the basis of differing sexual mating compatibility systems between S. sclerotiorum and B. cinerea. The organization of the mating-type loci differs, and their structures provide evidence for the evolution of heterothallism from homothallism. These data shed light on the evolutionary and mechanistic bases of the genetically complex traits of necrotrophic pathogenicity and sexual mating. This resource should facilitate the functional studies designed to better understand what makes these fungi such successful and persistent pathogens of agronomic crops

Impact des vagues sur la circulation océanique

Whole manuscript in english.Additional introduction and short conclusion in french.The purpose of this thesis is to study the impact of waves on the ocean circulation. The wave part is separated from the mean current and both are described differently. Many aspects are investigated. In the first part, the surface drift is analyzed with a one-dimensional model, with the use of a parameterization of the mixing induced by wave breaking. It appears that the Stokes drift of the waves generally dominates the Ekman drift at the surface. This description agrees with the orders of magnitude of the observations of turbulent kinetic energy dissipation, of Eulerian currents and of Lagrangian drifts. However, many aspects of this description, the Stokes-Coriolis effect for instance, have not been validated yet by observations. One reason is that one need a data set fully Eulerian or fully Lagrangian, long enough to allow the filtering out of other processes, with simultaneous observations of waves. A second part deals with the impact of waves on the mixing, and more particularly on the mixed layer depth. The diurnal mixed layer shows much sensitivity to the sea state. A waves reanalysis is used to estimate the parameters important for this mixing, as well as their global scale distributions. Finally, the waves / mean flow separation is studied close to the surf zone, and is compared to the other descriptions of the surf zone and inner-shelf dynamics. In particular, the impact of the waves non-linearity on the Lagrangian transports is evaluated.L'objectif de cette thèse est d'analyser l'impact des vagues sur la circulation océanique. La partie vagues est séparée du courant moyen et les deux sont décrites différemment. Divers aspects sont abordés. Dans la première partie, la dérive en surface est analysée à l'aide un modèle à 1 dimension, avec l'utilisation d'une paramétrisation du mélange lié au déferlement des vagues. Il apparaît que la dérive de Stokes des vagues domine la dérive d'Ekman en surface. Cette description apparaît cohérente avec les ordres de grandeurs des observations de dissipation d'énergie cinétique turbulente, de courants eulériens et de dérives lagrangiennes. Cependant, plusieurs aspects de cette description, l'effet Stokes-Coriolis par exemple, n'ont pas encore été validés par des observations. Une deuxième partie aborde l'impact des vagues sur le mélange et en particulier sur la profondeur de la couche de mélange. La profondeur de la couche de mélange diurne apparaît très sensible à l'état de mer. Une réanalyse de vagues est utilisée pour évaluer l'ordre de grandeur des paramètres importants pour ce mélange, ainsi que la distribution de ces paramètres à l'échelle globale. Enfin, la séparation des vagues et du courant est étudiée en zone côtière, aux abords de la zone de déferlement, et est comparée aux autres descriptions de la dynamique de la zone littorale et de ses abords immédiats. En particulier, l'impact de la non-linéarité des vagues sur les transports lagrangiens est évaluée

A global wave parameter database for geophysical applications. Part 2: Model validation with improved source term parameterization

A multi-scale global hindcast of ocean waves is presented that covers the years 1994-2012, based on recently published parameterizations for wind sea and swell dissipation [Ardhuin, F., Rogers, E., Babanin, A., Filipot, J.-F., Magne, R., Roland, A., van der Westhuysen, A., Queffeulou, P., Lefevre, J.-M., Aouf, L., Collard, F., 2010. Semi-empirical dissipation source functions for wind-wave models: Part I. Definition, calibration and validation. J. Phys. Oceanogr. 40 (9), 1917-1941]. Results from this hindcast include traditional wave parameters, like the significant wave height and mean periods, and we particularly consider the accuracy of the results for phenomenal sea states, with significant heights above 14 m. Using unbiased winds, there is no evidence of a bias in wave heights even for this very high range. Various spectral moments were also validated, including the surface Stokes drift and mean square slopes that are relevant for wave-current interactions modelling and remote sensing, and also spectra of seismic noise sources. The estimation of these parameters is made more accurate by the new wave growth and dissipation parameterizations. Associated air-sea fluxes of momentum and energy are significantly different from what is obtained with the WAM-Cycle 4 parameterization, with a roughness that is practically a function of wind speed only. That particular output of the model does not appear very realistic and will require future adjustments of the generation and dissipation parameterizations

Drift and mixing under the ocean surface revisited: Stratified conditions and model-data comparisons.

International audienceA one-dimensional model of the ocean near-surface currents is presented. It includes the enhanced near-surface mixing due to the waves, the wave-induced Stokes drift, the Stokes-Coriolis (SC) effect, and the stratification. Near-surface current shears from this model are compared with the shears of the quasi-Eulerian currents measured using a wave-following platform during the Shelf Mixed Layer Experiment (SMILE). It is shown that the downwind current shears observed during SMILE are well modeled. However, the observed crosswind shears are in poor agreement with the model. The Stokes-Coriolis (SC) term could qualitatively explain this misfit, but it is one order of magnitude too weak. The Ekman-Stokes spiral of the model is compared with the spiral observed during the long time series of measurements Long Term Upper Ocean Study 3. The effects of stratification are taken into account. The mean velocity profiles of the model closely agree with observations. However, there is no evidence of the SC effect on the shape of the observed current profile. The observed profile is found to be a consequence of the current rectification due to the time-varying stratification. The SC effect calculated from a numerical wave hindcast is weak but should have been observed. In fact, it is estimated that the wave-induced bias in the current measurements is larger than the SC effect. Finally, it is shown that the variation of surface drift with wave age, which was estimated to be small in unstratified conditions, is important in the presence of shallow mixed layers