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affiche; Bubble-plume characteristics including the population size-distribution, F, plume formation rate, P, and wave-characteristics were measured for mechanical, wind-steepened wave breaking in a large, fresh-water wind-wave channel for 13 m s-1 wind speed. Bubble plumes showed a wide diversity of F, physical extent, and dynamics, which were used to develop a classification scheme. The coupled evolution of wavebreaking, wave-properties, and bubble-plume characteristics were investigated. A significant differentiation amongst plumes was some plumes' ability to obscure optically (termed dense) the image background. Dense plumes (as opposed to diffuse plumes) were found to contain a large radius, r, peak in F - i.e., dense plumes are enhanced in large bubbles. Population is the total number of bubbles in the plume. Diffuse plumes are well-described by a shallowly decreasing F(r), for r < 1000 μm, and a more strongly decreasing F(r) for r > 1000 μm. For each class, P was determined and compared with the measured wave-breaking rate and wave characteristics with respect to fetch. The wave-breaking rate and intensity were strongly fetch dependent. In general, the trends in P and wave breaking are similar, reaching a maximum at the fetch of maximum wave breaking. The ratio of P for dense to diffuse plumes is even more sensitive to the occurrence of the most intense wave breaking, where dense plume formation is the greatest. Using P and the bubble-size population distributions for each plume class, the global bubble-plume, injection size-distribution, Yi(r), was calculated and decreased as r-1.2, for r < 1700 μm and Yi ~ r-3.9 for larger r. The volume injection rate for the study area was 640 cm3 s-1 divided approximately equally between bubbles smaller and larger than r ~ 1700-μm. The significance of dense versus diffuse plumes with respect to gas exchange of significant atmospheric gases was tested with a numerical bubble model and demonstrated that the large bubbles in dense plumes plays a very significant roll in the overall bubble-mediated air-water gas exchange, including the dependency of gas exchange on solubility and Schmidt number.

Meteorological and sea temperature data from the ODAS Italia 1 buoy (Ligurian Sea, Western Mediterranean) are used to study the anomalous warming of summer 2003 at sea. The event was related to the record heat wave that interested much of Europe from June to September of that year. The data show that the anomalous warming was prevalently confined to within a few meters below the sea surface. On the contrary, the temperatures in the underlying layers were lower than usual. The limited vertical propagation of heat is ascribed to the high temperature difference that arose between the surface and the deeper layers due to protracted calm weather conditions. The degree of penetration of heat deduced from the observations is consistent with that computed on the basis of an energetic argument, wherein the wind constitutes the sole supply of kinetic energy, while the heating is viewed as the source of potential energy that must be "subtracted" by mixing. The results support the hypothesis that the scanty energy from the wind is mainly responsible for the development of the temperature anomaly at the sea surface.

Wind wave development in the presence of a long mechanically-generated wave was investigated in the large IRPHE wind wave tank, for different wind speeds and long wave parameters. Wind and wave observations with and without long waves were made simultaneously at various fetches and compared. At short fetches, the wind wave field observed in presence of mechanical waves exhibits a broadened dominant spectral peak shifted towards low frequencies. At large fetches, the main effect of long waves on wind wave fields consists in a noticeable damping of the dominant waves. The damping factor increases rapidly with long wave steepness akL at small akL but no longer varies at large akL. Moreover, this factor is strongly wind dependent, increasing first up to 6 m/s, then decreasing significantly before reaching a saturation value at high wind speeds. Consistently, the wind-generated wave fields observed in presence of long waves are characterized by much lower equilibrium dominant wave steepness. Finally, the relevant mechanisms at the origin of these phenomena and their implications for ocean wave fields are discussed.

Measurements of breaking-wave-generated bubble plumes were made in fresh (but not clean) water in a large wind-wave tunnel. To preserve diversity, a classification scheme was developed on the basis of plume dimensions and "optical density," or the plume's ability to obscure the background. Optically dense plumes were due to the presence of a peak at large radius in the plume bubble size distribution. For each class, the plume formation rate, P, was measured at different fetches. The relationship between wavebreaking characteristics and the bubble plume evolution is examined in detail for these experiments. The wave-breaking rate and intensity were strongly fetch-dependent as the mechanically steepened wind waves rapidly evolved with fetch because of wind, dissipation, and nonlinear wave-wave interactions. P followed the trend in wave breaking, reaching a maximum at the fetch of maximum wave breaking. The ratio of dense to diffuse plumes was more sensitive to the wave-breaking intensity. Using P and the bubble population size distributions for each class, the global bubble plume injection size distribution, Ψi(r), where r is radius, was calculated. Ψi decreased as Ψi ∼ r-1.2 for r < 1700 μm and Ψi ∼ r-3.9 for larger r. Total volume injection was 640 cm3 S-1, divided approximately equally between bubbles smaller and larger than 1700-μm radius. Using plume volumes at maximum penetration for each class, a concentration distribution was calculated and showed plume concentrations greater than the background population by one to several orders of magnitude, depending upon r. Copyright 2006 by the American Geophysical Union.

Temporal and spatial characteristics of the resonant coupling between travelling air pressure disturbances and the middle Adriatic coastal waters are examined using a barotropic numerical model for a one year period (July 2000–July 2001). The model is forced by the travelling air pressure disturbances reconstructed from the 2-min resolution air pressure series measured at Split. Six experiments for the studied period are performed, in order to analyse the influence of the speed and disturbance direction on the resonant coupling. The first group of three experiments uses variable disturbance direction, whereas in the second three, a constant direction is employed during the whole experiment. Disturbance direction for the first group of experiments is computed from the 500-mb geopotential data provided by European Center for Medium Range Weather Forecast (ECMWF), as it is found that all of the past extreme events are correlated with them. Each experiment, with variable and constant disturbance direction, is repeated with three different constant values of 10, 20 and 30 m/s for the disturbance speed. The model verification on the Split sea level data reveals that the model reproduces most of the events but also overestimates/underestimates some of them and creates some false events due to the rigid assumption of a constant disturbance speed. The best agreement with data is obtained in the model runs assuming a disturbance speed of 20 m/s. A number of trapped and edge waves have been modelled at the constrictions and along the coast, in particular on a shoal that lies off Split perpendicular to the channel axis. The importance of the disturbance direction to the energy content is highlighted, particularly close to the shore, where the difference may be significant at 2–3 times on average, up to 30 cm in maximum amplitude.

International audience; Small scale surface waves in the capillary-gravity region can be easily advected by surface currents from all sources. Temporal measurements using fixed-point wave probes, therefore, cannot resolve reliably the spatial or wavenumber structure of short waves unless the surface currents are also monitored, which is an even more difficult task than surface wave measurement. A two-dimensional scanning slope sensor system is developed to perform 4D measurements [Ñh(x,y,t)] of small scale surface waves. The data yield 3D spectrum [B(kx,ky,w)] covering the capillary-gravity wave scales. Reflection of short waves as described by Shyu and Phillips (1990) can be clearly seen. The directional properties of small scale waves would be influenced by this mechanism greatly. These data can be used to investigate the balance of source functions in the wave action conservation equation following the approach suggested by Phillips (1984, 1985)

International audience; The effects of mechanically-generated long waves on wind-generated waves of shorter scales are investigated in laboratory as function of the different wind and long wave parameters. The modulation of short waves both in energy and scales along the long wave profiles is estimated respectively by means of the wavelet decomposition and the classical windowed Fourier transform methods, and the results are analysed within the framework of the recent coupled air-flow theories. The noticeable damping of the dominant waves in presence of a long wave is then quantified at the different stages of the wind wave field development. The relevant nonlinear mechanisms at the origin of these phenomena are discussed in the light of these observations.

Breaking-wave bubbles are important to many geophysical processes; however, few measurements have related the generated bubble distribution and plume characteristics with the wave evolution and plume dynamics. As part of the LUMINY wind-wave experiment, measurements of breaking waves, breaking-wave generated bubbles, and bubble plume characteristics were made in a wind tunnel for wind-stress breaking waves. Bubble plumes exhibited a wide range of bubble distributions, physical extents, and dynamics. A classification scheme was developed and the plume formation rate, P, at different fetches measured for approximately 3500 plumes. Bubble plumes were classified as major, minor, or micro depending upon physical plume dimensions. Plumes were also classified as diffuse or dense based upon their ability to obscure the background. Waves and wave breaking characteristics were determined for the experiments. Wave height was weakly dependant on fetch with peak wave height at the fetch of maximum wave breaking, 22.5 m. Wave height then decreased with greater fetch. In contrast, wave breaking depended strongly on fetch. P followed wave development and for micro and minor plumes occurred at the greatest fetch surveyed. The ratio of dense to diffuse plumes also followed the trend in wave development. Using the bubble-size population distributions for each plume class and P, the global bubble plume injection size distribution, Yi(r), where r is radius, was calculated. Yi decreased as Yi ~ r-1.2, for r < 1700 µm and Yi ~ r-3.9 for larger r. Volume injection rate for the study area was 640 cm3 s-1; divided approximately equally between bubbles smaller and larger than 1700-µm radius. Using plume volumes at maximum penetration for each class, a concentration distribution was calculated and showed plume concentrations greater than the background population by one to several orders of magnitude depending upon r.

Observations of effects of mechanically-generated long waves on wind-generated waves of shorter scales were carried out in the large IRPHE wind wave tank. Measurements of water surface heights and mean air flow parameters were made simultaneously by capacitance wave gauges and hot X-wire probes. The modulation of short waves both in energy and scales along the long wave profiles is the first striking effect observed. The modulation transfer function is estimated by two methods respectively based on the wavelet decomposition and the windowed Fourier transform and the results compared. The role of wind on the intensity and the phase of the modulation is thus analysed and discussed within the framework of the recent coupled air-flow theories. The second impact of long waves on wind wave fields consists in a noticeable damping of the dominant waves. This effect is quantified at the different stages of the wind wave development. The relevant mechanisms at the origin of this phenomenon are then discussed in the light of the results.

International audience; The work is concerned with the theoretical and experimental study of laminar-turbulent transition in the wind induced boundary layer in water beneath the free surface. The mechanism of this transition has not been identified yet and the present work is aimed to fill this gap. The experiments in the wave tank showed that the first perturbations which emerge out of natural primordial noise are long compared to the boundary layer thickness, then they gradually grow, become more nonlinear until suddenly a strong localised instability occurs. This instability results in almost immediate breakdown of the laminar boundary layer and formation of localised 3D turbulent spots. The spots slowly expand downstream forming turbulent streaks having the shape of upstream pointed arrowheads marked by the wind generated capillary-gravity waves on the water surface. The streaks merge further downstream creating basin-wide turbulence zone. The notable feature of the observed transition is that there is no universal critical Reynolds number, although the results are reproducible for the same values of wind. The critical distance Xc where the turbulent spots first appear is found to be inversely proportional to the wind stress at the surface. The theoretical study begins with the classical linear stability analysis carried out within the framework of Orr-Sommerfeld equation with the appropriate boundary conditions. In contrast to classical wall boundary layers, there are no linearly unstable modes. An analysis of weakly-nonlinear evolution of decaying perturbations under some unrestrictive assumptions suggests an unusual bypass scenario based on the explosive transverse instability of solitary waves as a plausible mechanism for the transition.

A very long data series (1921–2000) of hydrographic parameters (temperature, salinity and density) collected in surface and bottom layers at a station in the coastal zone in the northeastern Adriatic was analyzed. Seasonal and interannual variability of the three parameters is described on the basis of monthly and yearly averages. The seasonal cycles obtained were found to be typical for the northern Adriatic. Interannual analysis showed that there was no trend in temperature, salinity and density in the region during the interval analyzed. The long-term series of yearly means of hydrographic parameters were related to the long-term series of yearly means of several hydrological/atmospheric parameters using different time lags of between 0 and 4 years. These parameters are surface heat flux gained by insolation Qs computed for Trieste, precipitation P in Trieste, Po River discharge rate R and two atmospheric oscillation indexes, a Mediterranean Oscillation (MO) index and North Atlantic Oscillation (NAO) index. At zero time lag the interannual changes at the surface were found to be significantly related to changes in the Qs and NAO index (temperature) and R (salinity and density). At the same time lag the changes in the bottom were found to be related to the MO index (temperature, salinity and density). Additionally, bottom salinity and density were significantly related to R at a time lag of 1 year. Key words. Oceanography: Physical (air-sea interactions; hydrography)

International audience; The laminar-turbulent transition of wind-induced spatially developing surface boundary layer in water at the entrance of a water tank is investigated experimentally. Observations of the velocity field were made both by flow visualisation techniques using dye injection and laser Doppler velocimeter measurements. Two stages in the development of the perturbations have been clearly identified. First, a slow growth of streamwise longitudinal vortices embedded into the laminar flow is followed by a rapid development of secondary instabilities till to breakdown. The picture is similar to the by-pass transition to turbulence of a rigid plate boundary layer. At the second stage, peculiar to this flow, an explosive deepening of the boundary layer and fast development of inflexional instabilities occur. The critical fetch, where the shear boundary layer collapses and the first turbulent spots appear, is not linked to any critical Reynolds number but was found to be inversely proportional to the friction velocity squared.

Seasonal and year-to-year time evolution of the thermal structure, including the heat content change in the upper water column and its relationship with the surface net heat fluxes, have been studied at five locations in the central Mediterranean Sea. The study is based on temperature profiles collected during XBT surveys (eXpendable Bathy-Thermograph) carried out on ships of opportunity, in the framework of the MFSPP (Mediterranean Forecasting System Pilot Project), between September 1999 and May 2001. The five investigated zones are located in the southern Adriatic, NW Ionian, southern and northern Tyrrhenian, and Ligurian Sea. Gradual erosion of the thermocline in autumn, formation of a mixed layer in winter, and the onset of the stratification in spring, are common properties of the temporal evolution of thermal structures at all five locations. Moreover, in the southern Adriatic, a deep convection took place down to about 600 m in winter 1999/2000. On the other hand, mild climatic conditions and small surface heat loss in autumn and winter 2000/2001 drastically reduced a mixing/convection depth which hardly reached 200 m. Simultaneously, the NW Ionian remained slightly stratified throughout the winter period. The heat storage rate in the upper portion of the water column (down to 450 m) is compared with the air-sea net heat flux at a monthly scale. A heat content decrease is determined by the surface heat loss, and the processes such as lateral advection, or upwelling of the colder waters through the base of the water column (for example, in the southern Adriatic and Ionian Seas). Elsewhere (for example, in the northern Tyrrhenian and Ligurian Seas), the upwelling does not contribute significantly to the heat balance within the water column, since the vertical temperature gradients in deeper layers are negligible. Key words. Oceanography: general (climate and interannual variability; descriptive and regional oceanography) – Oceanography: physical (air-sea interactions)

9 páginas, 5 figuras, 1 tabla, [EN] Recent observations of newly formed deep water in the Aegean sea prompts this analysis of whether such deep water could be formed locally by the combination of an increase in net evaporation and wintertime water mass transformation. River diversion projects in Russia and Egypt since the 1950s have effectively increased the amount of net evaporation over the eastern Mediterranean basin. Historical profiles show that low salinity intermediate waters separated the deep and upper waters in the Aegean in 1961–1962. Within a simple mixed layer model, imposing a small net evaporation of 10 cm·yr–1 on the observed hydrographic conditions in March 1962 results in the gradual erosion of the low salinity intermediate waters. After 25 years, the low salinity intermediate waters are absent in agreement with observations made in September 1987. Continuing to force the model with the small net evaporation and with monthly heat and freshwater exchange anomalies from March 1987, new deep water could have been formed as early as March 1988. In the model, major deep water formation events occurred during the severe winters of 1991–1992 and 1992–1993 resulting in the formation of saltier and notably colder deep waters. The effective increase in net evaporation slowly increases the salinity and decreases the stratification in the Aegean sea until a severe winter leads to deep convection and new bottom water formation., [FR] Des observations récentes de l’eau profonde nouvellement formée en mer Égée permettent de déterminer si son origine est locale, suite à l’action combinée de l’évaporation nette et de la transformation hivernale de la masse d’eau. Les détournements des cours de rivières en Russie et en Égypte depuis les années cinquante ont en effet accru l’évaporation nette dans le bassin oriental de la Méditerranée. Des profils historiques montrent que les eaux intermédiaires de basse salinité séparent les masses d’eaux profonde et supérieure en mer Égée depuis les années 1961–1962. L’utilisation d’un modèle simple de couche de mélange où une évaporation nette de 10 cm·an–1 a été appliquée aux conditions hydrologiques observées en mars 1962 conduit à une diminution graduelle des eaux intermédiaires de basse salinité. Après 25 ans, ces eaux intermédiaires de basse salinité disparaissent, ce qui est en accord avec les observations réalisées en septembre 1987. Si l’on continue le forçage du modèle avec la même évaporation et en tenant compte des anomalies mensuelles des échanges de chaleur et d’eau douce depuis mars 1987, l’eau profonde « nouvelle » pourrait avoir été formée dès mars 1988. Avec ce modèle, des événements majeurs assurant la formation de l’eau profonde apparaissent. Durant les hivers rigoureux de 1991–1992 et de 1992–1993, des eaux profondes plus salées et notablement plus froides furent ainsi formées. L’accroissement de l’évaporation nette accroît progressivement la salinité et réduit la stratification en mer Égée jusqu’à ce qu’un hiver rigoureux entraîne une convection profonde et la formation d’une nouvelle eau de fond., This work has been carried out as part of the James Rennell Division’s research programme ‘Observing and modelling seasonal to decadal change in the ocean’ which is primarily supported by the Natural Environmental Research Council.

Font, Jordi... et al.-- 1 page, Satellite observation of ocean salinity has not been possible until now due to the challenge of ?ying a microwave radiometer able to detect sea surface emission variations related to salinity.The European Space Agency SMOS mission is the first attempt to solve this problem. A new radiometric concept and recent improvements in understanding the processes that modify the ocean water emissivity have made it possible. The WISE 2000 campaign has been conducted in the NW Mediterranean to obtain radiometric and in situ data to improve the understanding of the sea state effect on the sea surface L-band microwave emissivity

This study reports on a new formulation of the spectral dissipation source term Sds for wind-wave modelling applications. This new form of Sds features a nonlinear dependence on the local wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k)=k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for the onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is successfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields made with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closely with observations when compared to other dissipation source terms used in state-of-the-art wind-wave models. It also provides more flexibility in controlling properties of the wave spectrum within the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind input source functions and two alternative full-development evolution limits further demonstrate the robustness and flexibility of the new saturation-dependent dissipation source term. Finally, improved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.

Surface seiches and internal Kelvin waves are documented by the data collected in the Zadar and Pašman Channels during summer 1994, and are reproduced using analytic and numeric models. Energy loss at the head of the basin is allowed by imposing radiation condition there, while nodal line is enforced at the basin mouth. Surface seiches are found to be excited by a strong meteorological disturbance which occurred in late summer 1994, whereas internal Kelvin waves could be related to a meteorological perturbation which preceded deployment of the instruments.

Deep convection in the oceans, particularly at high latitudes, plays an important role in the climate systems of the world's oceans and atmosphere. This study was conducted to examine atmospheric forcing effects on deep convection in the Labrador Sea. The Naval Postgraduate School one dimensional ocean mixed layer model was applied to the Labrador Sea from February 12 to March 10, 1997. The model was initialized and forced with oceanographic and atmospheric data collected onboard the R/V Knorr during the first field program of the Labrador Sea Deep Convection Experiment. An ocean mixed layer depth close to 1300m was predicted and verified using the observed data. A sensitivity study was conducted using deviations from observations as input to determine how variations in atmospheric forcing could lead to the observed and even deepened ocean mixed layer. Observed Conductivity, temperature and depth (CTD) data were used to verify the model's spatial and temporal predictions of mixed layer temperature, salinity and depth. Model predicted mixed layer depths were usually slightly deeper than those observed. The final model output predicted temperature rather accurately, but model predicted salinity values were consistently low. A variety of sensitivity studies gave new insight to the individual influences of surface fluxes, momentum stresses, precipitation, salinity and individual storm variations to the mixed layer temperature, salinity and depth of the Labrador Sea. http://archive.org/details/airseinteraction109457863 Lieutenant Commander, United States Navy Approved for public release; distribution is unlimited.

A coupled, atmospheric-oceanic boundary layer model which provides a single station assessment and prediction capability has been developed from independently formulated one-dimensional oceanic and atmospheric bulk boundary layer models. Sensitivity analyses are conducted to determine major differences in the response of the coupled model compared to those of the separate oceanic and atmospheric models. The general behavior of the coupled model is not significantly different from that of the atmospheric model alone over short term simulations (12 co 2^ hours). However, under a certain set of limited conditions where winds are light and the lifting condensation level is close to the height of the inversion, large differences may occur. Major differences between the predicted evolution of the ocean boundary layer by the ocean model and coupled model are more common, and the short term predictive ability of the ocean model in coupled form is enhanced. http://archive.org/details/sensitivitynalys1094519548 Lieutenant Commander, United States Navy Approved for public release; distribution is unlimited.

The interaction of the northward component of planetary rotation and the east-west Reynolds stress affects the isotrophy of the integral scale turbulence in the upper ocean by redistributing turbulent kinetic energy (TKE) among the components. This "rotation stress" mechanism is incorporated into a vertically integrated model of the ocean mixed layer. Simulations of Ocean Weather Stations P (50˚N, 145˚W) and N (30˚N, 140˚W) are used to compare this model with the Garwood (1977) model and with observations. The significant effect is the augmentation (for easterly winds) or reduction (for westerly winds) of the ratio of vertical to horizontal TKE. The rate of entrainment is affected by the change in the vertical convergence of TKE at the interface between the mixed layer and the pycnocline. Rotation stress significantly alters the mixing on diurnal and synoptic time scales during late winter and early spring. With rotation stress, retreat events occur more frequently, and the mixed layer depth change during retreat is 10-30% greater than without rotation stress. Typically, the ratio of vertical to total TKE is three times larger when rotation stress is included and the dissipation enhancement of Garwood (1977) is neglected. The resulting TKE distribution is more isotropic and in better agreement with laboratory results for neutrally stratified shear flows. This study demonstrates the need for measurements of the TKE budget in the upper ocean to confirm these findings and to further test the hypotheses of TKE models in oceanic applications. ONR, NSF http://archive.org/details/importanceofrota1094522289 ONR, NSF Approved for public release; distribution is unlimited.