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20 pages, 24 figures, 4 tables.-- Data availability: Data will be made available on request, Diapycnal mixing in the Brazil-Malvinas Confluence Zone (BMC) is assessed on the basis of microstructure measurements done as part of an April 2017 cruise, which explored the mesoscalar and regional frontal dynamics. Sampling was done down to 400 m in 11 locations on both sides of the BMC, over the slope and in the abyssal waters. Turbulent scales, non-dimensional numbers, energy dissipation rates and diapycnal eddy diffusivities are calculated, which allow us to assess the state of the small-scale turbulence in the frontal region. Active turbulence was present at all depths and stations, with high-dissipation patches ranging from several metres to a few tens of metres. The frontal zone is characterized by high energy dissipation and eddy diffusivity. The geometric mean eddy diffusivity for all stations and the entire water column is 7.0 × 10-4 m2 s−1. The mean values halve when only considering the more stratified seasonal thermocline, 3.8 × 10-4 m2 s−1, and are twice larger south than north of the BMC. High dissipation rates coincide with high vertical shear, possibly related to the convergence of the two intense currents and/or the generation of internal waves by the associated mesoscalar and submesoscalar features. The layered structures related to intruding filaments favor double diffusive convection and salt fingering. Near-bottom mixing at the stations on the continental slope is possible related to shear-driven Kelvin-Helmoltz instabilities, This study has been supported by the Spanish Government through projects VA-DE-RETRO (CTM2014-56987-P) and SAGA (RTI2018-100844-B-C33), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

11 pages, 7 figures, 3 tables, This dataset, gathered during the RETRO-BMC cruise, reports multiple-scale measurements at the Confluence of the Brazil and Malvinas Currents. The cruise was carried out between 8 and 28 April 2017 onboard R/V Hespérides, departing from Ushuaia and arriving to Santos. Along its track, the vessel recorded near-surface temperature and salinity, as well as the horizontal flow from 20 m down to about 800 m. A total of 33 hydrographic stations were completed in a region off the Patagonian Shelf, within 41.2°S–35.9°S and out to 53.0°W. At each station, a multiparametric probe and velocity sensors were deployed inside the frame of a rosette used to collect water samples at selected depths; these samples were later used for several water analyses, including inorganic nutrient concentrations. Microstructure measurements were carried out in 11 of these hydrographic stations. In addition, two high-resolution three-dimensional surveys were conducted with an instrumented undulating vehicle between 40.6°S–39.0°S and 55.6°W–53.8°W. Lastly, eight high-frequency vertical profilers were deployed in the region and five position-transmitting drifters were launched. These data allow the description of the Confluence from the regional scale to the microscale, and provide a view of the variability of the frontal region on time scales from days to weeks, This research has been supported by the Spanish government (Ministerio de Economía and Competitividad through project VA-DE-RETRO, CTM2014-56987-P, and Ministerio de Ciencia, Innovación y Universidades through project SAGA, RTI2018‐100844‐BC33). Dorleta Orúe-Echevarría (FPU2013-02884) and Ignasi Vallés-Casanova (BES‐2015‐071314) have also been funded with PhD scholarships by the Spanish government (Ministerio de Ciencia, Innovación y Universidades). Paola Castellanos has been partly supported by the Portuguese government (Fundação para a Ciência e a Tecnologia through project COASTNET, PINFRA/22128/2016), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Described is the impact of the Aral Sea desiccation on the local climate and the impact of its numerical prediction in the region. Presented is the analysis of two series of numerical experiments with the WRF-ARW model (numerical prediction and weather research) with the spatial resolution of 5 km and 28 σ-surfaces along the vertical up to the level of 50 hPa for the Aral Sea region. In the first series of forecasts for January and July 2009, underlying surface parameters from the MODIS database are used. In these series the sea surface mask corresponds to the Aral Sea configuration in the 1970s. In another group of experiments, the characteristics of the underlying surface of the Aral Sea area are replaced by the respective characteristics of the surrounding land. To study the effects of variations of surface properties, air temperature, humidity, cloudiness, precipitation, and wind are analyzed. It is demonstrated that if the Aral Sea is assumed to be absent in the model, this results in the significant strengthening of the continentality of regional climate and in the increase in the forecast skill scores. The supposition is made that the regular (at least each 3–5 years) update of global databases with the description of underlying surface properties due to the climate change can result in the considerable increase in the accuracy of numerical prediction and climate change modeling Text original de l'article en rus: Ó K.G. Rubinshtein, M.M. Smirnova, V.I. Bychkova, S.V. Emelina, R.Yu. Ignatov, V.M. Khan, V.A. Tishchenko, E. Roget, 2014, published in Meteorologiya i Gidrologiya, 2014, No. 11, pp. 24-35.

Internal standing waves (seiches) in the South Aral Sea are studied for the first time. The study, based on numerical simulations and field data, focuses on two different campaigns: the first in autumn 2006, when the stratification was weak and there was a mild prevailing northeasterly wind, and the second in autumn 2013, when the stratification was strong and there was a mild easterly wind. Between these two campaigns, the sea surface level decreased by 3.2m. The periods of the fundamental modes were identified as 36 and 14h, respectively. In both years, either second or third vertical modes were found. In general, the vertical modes in 2013 were higher because of the broad and strong pycnocline. For both years, it was found that the deep quasi-homogeneous mixed upper layer could sustain internal waves under mild wind conditions. The observed first and second vertical modes in 2006 are the first and second horizontal modes and the second and third vertical modes in 2013 are the second and third horizontal modes. The results suggest that, due to sea level variations, the neck connecting the Chernyshev Bay to the main body of the lake can become a critical location for the development of a nodal line for all principal oscillation modes. Rotation effects on waves were not analyzed in this study The present work was carried out within the framework of the CLIMSEAS exchange project funded by the European Commission (ref. FP7-IRSES-2009-247512). Field work was supported by Russian Science Foundation grant 14-50-00095

Velocity measurements with vertical resolution 0.02 m were conducted in the lowest 0.5 m of the water column using acoustic Doppler current profiler (ADCP) at a test site in the western part of the East China Sea. The friction velocity u * and the turbulent kinetic energy dissipation rate e wl(ζ) profiles were calculated using log-layer fits; ζ is the height above the bottom. During a semidiurnal tidal cycle, u * was found to vary in the range (1–7) × 10−3 m/s. The law-of-the-wall dissipation profiles e wl(ζ) were consistent with the dissipation profiles e mc(ζ) evaluated using independent microstructure measurements of small-scale shear, except in the presence of westward currents. It was hypothesized that an isolated bathymetric rise (25 m height at a 50-m seafloor) located to the east of the measurement site is responsible for the latter. Calculation of the depth integrated internal tide generating body force in the region showed that the flanks of the rise are hotspots of internal wave energy that may locally produce a significant turbulent zone while emitting tidal and shorter nonlinear internal waves. This distant topographic source of turbulence may enhance the microstructure-based dissipation levels e mc(ζ) in the bottom boundary layer (BBL) beyond the dissipation e wl(ζ) associated with purely locally generated turbulence by skin currents. Semi-empirical estimates for dissipation at a distance from the bathymetric rise agree well with the BBL values of e mc measured 15 km upslope.

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate e and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding. A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of e computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute e from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations. Statistical analysis of eddy Kb and thermal Kθ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between Kb and Kθ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged Kb and Kθ differ significantly, which may point to the inapplicability of isotropic formulae used for e and temperature dissipation χθ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.

Microstructure, ADCP and CTD profiles taken in the North Atlantic along 53°N under moderate and high winds showed that the median of log-normally distributed kinetic energy dissipation rate e within the upper mixing layer is 1.5×10−7 W/kg and the layer depth, on the average, is ∼40 m. Assuming that mixing efficiency γ is a constant ( γ = 0.2 ), the following scaling is proposed for the normalized eddy diffusivity: K ^ b = K b / κ u * z = ( 1 + Ri / R i cr ) - p P r tr - 1 , where K b = γ e / N 2 , N2 is the squared buoyancy frequency, u * the surface friction velocity, Ri the local Richardson number, P r tr = 1 + Ri / R i β the turbulent Prandtl number, p = 1 or 2/3, Ricr=0.1 and Riβ=0.1 or 0.05. The power-law function with p = 1 relates the asymptotes of Kb(Ri) to the buoyancy scale L N ∼ ( e / N 3 ) 1 / 2 at Ri⪢Ricr and to the shear scale L Sh ∼ ( e / Sh 3 ) 1 / 2 at Ri⪡Ricr. If p = 2 / 3 , the lengthscale L R = ( e / N 2 Sh ) 1 / 2 replaces LN in spectra of ocean microstructure than due to the influence of local shear. This mixing regime corresponds to intermediate Richardson numbers (∼0.25 Alternatively, if γ is not a constant, but an increasing function of Ri for 0 K ^ b ( Ri ) shows a very weak dependence on Ri for Ri K ^ b ( Ri ) is used.

Microstructure profiling measurements taken on a shallow Black Sea shelf and in Lake Banyoles and Boadella reservoir (Both in Spain) are analyzed to investigate the influence of boundary-layer-induced turbulence of various sources on mixing in the water interior. The state of turbulence in shallow waters is examined and details of microstructure data processing and error analysis are discussed. The dependence between averaged activity parameter (average)A(subscript G) and buoyancy Reynolds number (average)Re(subscript b) for the shelf turbulence indicates that for (average)Re(subscript b)＜1 the state of turbulence can be described by the fossil turbulence model, which postulates A(subscript G)~Re(superscript 1/2 subscript b). For (average)Re(subscript b)＞1, however, the influence of (average)Re(subscript b) on (average)A(subscript G) is weak, signifying that the buoyancy Reynolds number can no longer serve as the governing parameter for active turbulent mixing. The generation of turbulence by a one-minute long wind bursts (the Boadella reservoir) increases the averaged dissipation rate 〈e〉of the surface mixed layer by more than 5 times (up to 3×10^(-6) W kg^(-1)). The influence of the wind bursts was also traced below the thermocline, where turbulent patches with 〈e〉=(10^(-7)-10^(-6)) W kg^(-1) were generated. It is shown that the geothermal convection in Lake Banyoles produces intermittent turbulent patches with characteristic dissipation rate 〈e〉=(2×10^(-8)-3×10(-7)) W kg^(-1), which influences the overall vertical mixing in the basin.

High vertical wave-number modes clearly dominate the internal wave field during the stratification period in Boadella reservoir in northeast Spain. In this period, the extraction of hypolimnetic water, due to summer irrigation, brought the surface level down by 6 m in one month and the epilimnetic water progressively occupied the whole water column. The temperature profile, with the exception of a few meters at the surface layer, presented an almost constant temperature gradient of about 0.7°C/m. The period of the main vertical mode is 24 h with an amplitude of around 1 m. Thermistor chain records and meteorological data allow us to deduce that this mode is, at least, a third vertical mode forced by the wind, which normally has a typical periodicity of 24 h. However, when the wind changes direction from south to north, the circulation cells developed due to this forced nonstationary oscillation are destroyed. When this occurs, the Bulk Richardson number is Ri\db~1. Similar vertical structures as a response to wind forcing should be expected in similar systems, although this has not been reported in the literature.

From the analysis of thermistor chain data recorded in a small clongatcd lake, compared with the results of numerical simulations, second vertical modes of the internal scichcs are shown to be active during more than twothirds of the whole stratifcd period, although no rcsonancc with the wind is observed. On the other hand, due to the wind pattern, transversal seiches (mainly the first vertical mode) are also usually excited and they somctimcs dominate. At the end of the stratified period, however, when the thermocline is very sharp, first vertical modeslongitudinal and transversal-are the only ones that are excited. Finally, due to the wind, a forced oscillation of the whole lake is excited. After Mortimer (1952), who brought up to date both the earlier descriptions of internal seiches in Loch Ness (Watson 1904) and their further interpretations (Schmidt 1908; Wedderburn 1907; Wedderburn and Young 1915), internal seiches have been recognized as an everyday feature of movement in stratified water systems subject to wind action (Marmorino and Mortimer 1978; Hutter 1993; Korgen 1995). Now, the relevance of the internal seiches is widely documented: the structure of the horizontal velocities in the water column may determine the regions where the shear is strong enough to create instabilities leading to turbulence that might facilitate the resuspension of bottom sediments (Wiegand and Chamberlain 1987); the periodic vertical displacements of the internal seiches can advect the suspended algal cells, forcing them to be exposed to variations in light intensity (Webster 1990; Gaedke and Schimmele 1990); and internal scichcs greatly support the flux path of the transference of energy from the wind to the hypolimnion (Imberger 1994).

Extensive field data of a density current driven by the differences in the cooling rates between the two lobes of a small lake are presented. These data illustrate the fact that this gravitational motion affects the whole system and dominates its lakewide circulation. Moreover, data are used to evaluate the entrainment into the density current and also to discuss the regime of the flow from a scaling analysis of the horizontal momentum equations. This analysis is specifically applied to the central area of the lake, where the density current flows from one lobe to the other. Results of this study show that in the longitudinal direction there is a balance between the pressure gradient and the turbulent viscous term. Further, it is found that geostrophy correctly describes the transversal pattern of the passage of the gravity current from the northern lobe to the southern, where it flows confined to the western shoreline.

Text original de l'article publicat en rus: V.A. Tishchenko, V.M. Khan, R.M. Vil’fand, E. Roget, 2013, published in Meteorologiya i Gidrologiya, 2013, No. 7, pp. 15-30 Carried out are the statistical analysis of spatiotemporal characteristics of quasistationary and blocking anticyclones in the Atlantic European sector, their classification, and the analysis of large-scale circulation in the lower and middle troposphere preceding the formation of different classes of blocking anticyclones. Studied are the threshold conditions of anticyclone blocking in the lower and middle troposphere in the Atlantic European sector. Determined are the typical situations, when the formed dipoles of heat and cold are observed in the area of the future blocking in the lower troposphere as well as the formed ridges or divergence of flows in the middle troposphere. A conclusion can be made on the possibility of using the information about blocking anticyclones in the schemes of long-range forecasting of thermal regime

The scope of this work is to quantify the upflows through the underground sources in the bottom of Lake Banyoles (NE-Iberia). The method applied uses the mean settling rate and the fraction of solids per unit of volume of the suspensions at the underground sources, and also the horizontal areas covered by these suspensions. The results obtained reveal that about 90% of the total underground inflow enters the lake through one of the sources. This result agrees with the total underground inflow calculated from the difference of the surface in and outflow of the lake. The behaviour of the suspensions at the underground sources was in a accordance with the theory used to developed the measuring method. Finally, the degree of turbulence in the upper part of the suspension and the importance of the transmissivity of the limestone layer next to the lake are discussed and are found to be negligible.

Resuspension of sediment by subterranean springs occurs in karstic, multibasin Lake Banyoles, Spain. The sediment at the bottom of one of the basins was consolidating when intrusion of groundwater caused resuspension. Here, the lutocline rose nearly 20 m over 10 months. During this episode temperature profiles, sediment size distributions, bulk density, and settling rates showed that the jet-generated turbulence produced strong mixture in the central core of the conic depression forming the basin. Data from another basin where the sediment was always in suspension are presented for comparison. Here, the stratification in density and settling rate of the particles suggest sorting out of the aggregates, with the largest flocs occupying the deepest parts of the basin.

Lake Banyoles is a multibasin lake dominated by groundwater derived inflows. It is composed of three major basins, two of them being meromictic. The relatively warm and saline groundwater inflows, together with the basin morphometry, give rise to characteristic thermal structures in each basin, with different thermocline levels and temperature inversions distinguishing the basins. A one-dimensional lake mixing model has been adapted to include the form of mixing associated with the groundwater inflows, and the results are compared with data collected from the lake.

Because of the difference in morphometry and in the underground heating of the two lobes of Lake Banyoles there is a differential cooling that causes a density current — the denser water of the shallower lobe plunging into the deepest lobe forming a bottom current — which redistributes water between the lobes and replaces that of the northern lobe about every 5 days. This current has been studied during the mixing periods of the years 1989–1991 from temperature and current measurements and it has been found that it increases or slows down depending on the direction of the wind. Furthermore, it is observed that it mainly flows along the west shore of the lake, deflecting towards the right as an effect of the bottom morphometry. However, due to the long time scale of the density current the influence of the earth's rotation should not be neglected in advance. Finally, a simple numerical model has been used to corroborate the magnitude of this current — whose velocity has been directly measured — which is found to be the most important in the lake during the mixing period and so, it dominates the lake-wide circulation

[1] Microstructure measurements of a triple-diffusive staircase with a stability ratio of 1.1 are presented. Data were recorded at Lake Banyoles, a small lake in Catalonia, Spain, with a warm, salty, and turbid underground inflow. Turbulent scales are well resolved in the two observed convective layers and allow determination of the dissipation rates of the turbulent kinetic energy, ɛ, and of the turbulent temperature fluctuations, χ, which are found to be 3.3 × 10−7 C2/s and 2.7 × 10−9 W/kg for one of the layers and 5.9 × 10−7 C2/s and 3.8 × 10−9 W/kg for the other. Thermal spectra for the convective layers look universal in viscous-diffusive and viscous-convective subranges. Characteristic vertical displacements within convective layers could also be obtained on the basis of Thorpe scales and were found to be 0.3 times the layer thickness. Vertical convective fluctuations were estimated and found to be of the order of 10−4 m/s. When turbulent fluxes were determined within the convective layers on the basis of microstructure data and compared to those at the diffusive interfaces, they showed a stationary state with a mean thermal flux of 3.5 × 10−6 C m/s. A comparison of experimental heat fluxes to different models favors the scaling model of Grossman and Lohse (2000) for Rayleigh-Benard convection and the double-diffusive convection model of Fernando (1979a, 1979b) for low stability. If the 4/3 power law is assumed, then the parameterization proposed by Taylor (1988) for diffusive interfaces at low values of the density ratio is also in accordance with our data.

[1] The dependence of the mixed layer depth hD on the sea surface fluxes is analyzed based on measurements taken along a cross-Atlantic section 53°N. A linear function hD ≈ 0.44Lf, where Lf = u*/f is the Ekman scale, well represents the influence of the wind stress u* and rotation f on the mixed-layer deepening, thus indicating that the influence of convective mixing in late spring at this latitude is of a lesser importance. Also, data showed reasonable correlation of hD with the stratified Ekman scale LfN = u*/, where Npc is the buoyancy frequency in the pycnocline, according to hD ≈ 1.9LfN. In both cases the highest correlation between hD and the corresponding lengthscales is achieved when u* values taken 12 hours in advance of the mixed layer measurements were used, which may signify the adjustment time of inertial oscillations to produce critical shear at the base of the mixed layer. The vertical profiles of the dissipation rate ɛ(z) are parameterized by two formulae that are based on the law of the wall scaling ɛs(z) = u*3/0.4z and the buoyancy flux Jb: ɛ1(z) = 2.6ɛs(z) + 0.6Jb and ɛ2(z) = ɛs(z) + 3.7Jb. The first parameterization is used to calculate the integrated dissipation int over the mixing layer, which was found to be ∼3–7% (5% on the average) of the wind work E10. The positive correlation between hD and int/E10 suggests that in deeper quasi-homogeneous layers a larger portion of the wind work is consumed by viscous dissipation vis-a-vis that is used for entrainment. As such, the mixing efficiency, which is based on integral quantities, is expected to decrease with the growth of the mixed layer.

A hydrothermal plume with vertical and horizontal length scales of ~18 and ~300 m, respectively, develops in a karstic lake. The plume is generated at the bottom of a basin that contains sediment in suspension, which is at a higher temperature than the water immediately above (the hypolimnion of the lake). The rising convective plume entrains colder hypolimnetic water and develops upward, until it reaches the base of the seasonal thermocline, carrying an important amount of sediment particles from the bottom, which are used as tracers to describe the spatial distribution of the plume. At the level of neutral buoyancy, the plume spreads laterally, as a horizontal baroclinic intrusion.

The Princeton Ocean Model was applied to the Sau Reservoir, a medium-sized Mediterranean reservoir (5.7 km2) located in Catalonia, Spain, during the summer season, when the water column is continuously stratified and forced by a breeze regime with velocities of up to 3-4 m/s. Based on our simulations, the internal wave field has been analysed and the numerical results compared with the field data previously analysed by other authors. The model adequately reproduces all the significant modes observed. The simulations show the importance of rotational modes on the internal wave field. The Burger number S for all rotating internal waves is on the order of 10−1, and the internal Rossby radius R is on the order of 102 m, that is, smaller than the width of the lacustrine area of the reservoir (103 m). Specifically, two rotating third vertical modes were found during the analysed period: the first, a 24-hour period, was forced by the wind and the phase rotated clockwise; and the second, a 12-hour period, can be interpreted as a second azimuthal horitzontal mode of a Poincaré wave. A second vertical mode of 8 hours was observed to rotate counter clockwise, although in this case the Earth’s rotation appears not to have been of importance because the same results could be obtained without taking into account the Coriolis force. Finally, two first vertical modes, one of 6 hours and the other of 5 hours, were observed, although with no rotational behaviour. These modes correspond, respectively, to the first and second horizontal stationary modes. Further analysis of the simulated velocities shows the existence of a net clockwise flow along the shore as a consequence of the dominant mode of 24 hours, with a mean velocity of 0.5 m/s that reverses at a distance of about 300 m from the coast. Preliminary results based on the simulated velocity field predict horizontal trajectories of passive particles of up to 1 km per day and vertical displacements of up to 5 m across the entire water column El Princeton Ocean Model ha sido aplicado al embalse de Sau, un embalse Mediterráneo de tamaño mediano (5.7 km2), situado en Cataluña, España, durante la estación de verano cuando la columna de agua esta estratificada de forma continua y forzada por un régimen de brisa con velocidades de hasta 3-4 m/s. Basándonos en estas simulaciones hemos analizado el campo de ondas internas y comparado los resultados numéricos con datos experimentales ya analizados por otros autores. El modelo reproduce adecuadamente todos los modos significantes observados. Las simulaciones muestran la importancia de los modos rotacionales en el campo de ondas internas. El número de Burger S para cada una de las ondas internas rotacionales es del orden de 10−1 y el radio de Rossby interno R del orden de 102 m, más pequeño que la anchura de la zona lacustre del embalse (103m). Más precisamente, durante el periodo analizado, se encuentran dos terceros modos verticales con rotación: el primero de 24 horas era forzado por el viento y con rotación horaria de la fase, y el segundo de 12 horas es interpretado como una onda de Potincare del segundo modo horizontal acimutal. También, se observa un segundo modo vertical de 8 horas con rotación anti horaria, aunque en este caso la rotación terrestre no tiene importancia porque los mismos resultados pueden ser obtenidos sin tener en cuenta la fuerza de Coriolis. Finalmente, son observados dos primeros modos verticales, uno de 6 h y otro de 5 h, aunque sin comportamiento rotacional. Estos modos corresponden al primer y al segundo modos estacionario horizontal, respectivamente. Un análisis ulterior de las velocidades simuladas con el POM muestran la existencia de un flujo neto a lo largo de la costa, derivado del modo dominante de 24 horas con una velocidad promedio de 0.5 cm/s que se invierte a una distancia de la costa de aproximadamente 300 m. Resultados preliminares basados en el campo de velocidades simuladas predicen unas trayectorias horizontales de las partículas pasivas de hasta 1 km por día y unos desplazamientos verticales de hasta 5 m a través de la columna de agua Our study was supported by the SpanishGovernment through grants REN2001-2239 and FIS2008-03608

13 páginas, 8 figuras, 3 tablas., A new method based on wavelet denoising and the analysis of Thorpe displacements dT profiles is presented for turbulent patch identification. Thorpe profiles are computed by comparing the observed density profile r(z) and the monotonic density profile rm(z), which is constructed by reordering r(z) to make it gravitationally stable. This method is decomposed in two main algorithms. The first, based on a wavelet denoising procedure, reduces most of the noise present in the measured profiles. This algorithm has been tested from theoretical profiles and has demonstrated a high efficiency in noise reduction, only some limitations were detected in very low-density gradient conditions. The second algorithm is based on a semiquantitative analysis of the Thorpe displacements. By comparing each displacement dT with its potential error EdT, it is possible to classify samples in three possible states: Z (dT 5 0), U (dT , EdT), and S (dT . EdT). This classification makes it possible to compute two statistical indexes: the displacement index ID, the quotient between the number of S values and the number of averaging points; and the uncertainty index IU, the quotient between the number of points on state U and the number of averaging points. The displacement index ID has been used as the parameter for turbulent patch identification, identifying the patches as segments with strict positive ID values. To illustrate the method, a number of field profiles covering a wide density gradient range were analyzed. Turbulent patches were validated following the tests proposed by Moum and Galbraith and Kelley. The high percentage of validating patches indicates that the proposed method is very efficient even at very low-density gradients where the potential error on dT is high, and shows that it is a powerful tool for turbulent patch identification., This work was partially supported by the Spanish government (DGCIYT).

Lake Banyoles, of karstic origin, is continually heated by the incoming groundwater. This water enters the lake at certain places which are basin-shaped, keeping sediment in suspension. The temperature of suspended sediment is 2°–3°C higher than that of hypolimnetic water in summer, and 8°–10°C higher in winter. Because of this the cooling of the lake is measurably lessened. In this work a model to calculate the heat flux from underground is presented where both diffusive and advective heat fluxes are considered. The degree of turbulence of the water at the interface of suspended sediment is also evaluated. Finally, this model is applied over a 1-year cycle.

Combining a six-term heat balance equation and a seasonal thermocline model, a new equation to calculate non- radiative fluxes of Lake Banyoles has been determined. Mean daily measurements of global solar radiation, downward longwave radiation, wind speed, air temperature and water surface temperature were used as input data and lake temperature as the calculated output data of the model. To calibrate performance of the new equation, calculated lake temperature was compared with measured lake temperature during both the mixing and the stratified period of the lake. The new coefficients in the wind function to calculate the non-radiative fluxes at the water surface were assumed to depend on the variability of the wind speed, the air temperature of the study area and the surface temperature of the lake. In addition, the results were used to estimate the heat balance of the air–water interface of Lake Banyoles over a period of two years. The processes that have been taken into account are shortwave and longwave radiation, back-radiation emitted by the lake, sensible and latent heat and throughflow.

Suspension of sediment by subterranean springs is a very common phenomena in the karstic, multibasin Lake Banyoles. The flow of groundwater into the lake introduces a suspension of marly and argilaceous materials. The temperature of this slurry is nearly constant throughout the year, around 19°C. The lake is formed by 6 basins and at the bottom of these basins there are 12 sources where the presence of suspended material signifies entering groundwater (Figure 1). Suspension of bottom lake sediment by groundwater is a feature of Lake Banyoles that has not been described elsewhere. Here we present experimental results which show that the maximum height that the sediment can rise to is affected by the formation of aggregates.

Reasons for the existence of the channel connectin the two lobes of the present Large Aral Sea are discussed. In situ measurements in 2005 show that differences between the measured depths and those contained in the available digital bathymetry of the lake are considerably different at the channel (7.5±0.9 m, at nine measurement stations along it) and at the northern part of the eastern lobe (1.6±0.3 m, at six stations from the western to the eastern shore). Differences in the misfits observed in the two zones are discussed and thought to be a consequence of the variation of the transversal area of the channel as it enters the eastern lobe, which would affect the flow velocity and thus the strength of the erosion process at the bottom. Field data together with satellite images have been used to modify an original digital bathymetry of the lake and have been implemented into a 3-D hydrodynamical model. A numerical simulation shows that a wind of 12 m/s blowing from the east (112°) generates velocities of up to 45 cm/s in the channel, allowing denser water from the eastern lobe (salinity: 132 g/kg) to flow about 38 km towards the fresher western lobe (salinity: 98 g/kg) in one day. The effect of the inflow on the vertical structure of the western lobe is also illustrated. Although nowadays the channel will be soon a thing of the past, in a more general context, the Aral Sea is presented as an example showing that geomorphologic and geophysical processes, along with hydrological and atmospheric processes, must be taken into account for short-term predictions We thank D. Soloviov and S. Stanichniy (Marine Hydrophysical Institute, Ukraine), who kindly provided the satellite images used in this study. We are grateful to Professor Micklin and one anonymous reviewer for the interesting points they have raised in their review and for the opportunity to incorporate them in the text. This paper has been done within the frame of the NATO Collaborative Linkage Grant ESP-NR-NRCLG-982592. The work was also supported by the Russian Foundation for Basic Research and, partially, by the Spanish Ministry of Education and Science, grant FIS2008-03608 This paper has been done within the frame of the NATO Collaborative Linkage Grant ESP-NR-NRCLG-982592. The work was also supported by the Russian Foundation for Basic Research and, partially, by the Spanish Ministry of Education and Science, grant FIS2008-03608

[1] Statistics of microstructure patches in a sheared, strongly stratified metalimnion of Lake Banyoles (Catalonia, Spain), which occupied ∼40% of the total lake depth of 12 m, are analyzed. Light winds ( 0.25 m, the ratio LTp/hp depends on the patch Richardson and mixing Reynolds numbers following the parameterization of Lozovatsky and Fernando (2002). Analysis of the dynamics of mixing reveals that averaged vertical diffusivities ranged between ∼1 × 10−4 m2 s−1 and ∼5 × 10−5 m2 s−1, depending on the phase of the internal waves. Episodic wind gusts (wind speed above 6 m s−1) transfer ∼1.6% of the wind energy to the metalimnion and ∼0.7% to the hypolimnion, generating large microstructure patches with hp of several meters

Special volume: Advances in Spanish physical oceanography. Scientia Marina 76(Suppl.1) 2012.-- 13 pages, 12 figures, 1 table, [EN] Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one, [ES] Se presentan datos de turbidez, CTD y microestructura (temperatura y cizalla) a lo largo de un transecto a través de la plataforma continental del Delta del Ebro, desde 8 a 69 m de profundidad, en la parte noroeste del mar Mediterráneo. La columna de agua estaba estratificada e inmediatamente antes de la campaña la corriente cerca del fondo presentaba periodicidades diarias y sub-inerciales. La extensión vertical de la capa de fondo (BBL) en las estaciones más profundas de 20 m varía entre 3 y 9 metros, pero alcanza los 12 m en la estación más profunda y es de 14 m en otra estación situada a 45 m de profundidad no incluida en el transecto. Se ha detectado la existencia de la ley de la pared en casi todas las estaciones, ocupando una extensión entre el 40% y el 100% de la BBL. En algunas estaciones la disipación aumenta en el interior de la BBL. Los datos muestran la correspondencia en la BBL entre la distribución de turbidez y los procesos físicos de mezcla locales y sugieren que la reflexión cuasi crítica de las ondasinternas podría jugar un papel importante en la mezcla en el fondo. Nuestros datos tanbien sugieren que durante la campaña y después de dos cortos episodios de viento fuerte, la estructura baroclínia cambió de un primer a un segundo modo, We are grateful to M. Demestre for allowing us to be on board the Garcia de Cid within the context of the VEDA Project and the EU RESPONSE (Q5RS-2002-00787) project and for facilitating the measurements. [...] This paper was finished in accordance with the objectives of the project CGL2008-03608 funded by the Ministry of Science and Innovation of the Spanish Government and within the framework of the CLIMSEAS Project (FP7-PEOPLE-2009-IRSES N. 247512)

The theoretical models of Batchelor and Kraichnan, which account for the smallest scales of a scalar field passively advected by a turbulent fluid (Prandtl . 1), have been validated using shear and temperature profiles measured with a microstructure profiler in a lake. The value of the rate of dissipation of turbulent kinetic energy « has been computed by fitting the shear spectra to the Panchev and Kesich theoretical model and the one-dimensional spectra of the temperature gradient, once « is known, to the Batchelor and Kraichnan models and from it determining the value of the turbulent parameter q. The goodness of the fit between the spectra corresponding to these models and the measured data shows a very clear dependence on the degree of isotropy, which is estimated by the Cox number. The Kraichnan model adjusts better to themeasured data than the Batchelor model, and the values of the turbulent parameter that better fit the experimental data are qв 5 4.4 ± 0.8 and qK 5 7.9± 2.5 for Batchelor and Kraichnan, respectively, when Cox ≥ 50. Once the turbulent parameter is fixed, a comparison of the value of « determined from fitting the thermal gradient spectra to the value obtained after fitting the shear spectra shows that the Kraichnan model gives a very good estimate of the dissipation, which the Batchelor model underestimates This research was developed under Spanish Government Project FIS2008-03608. We would also like to thank Francesc Nogue´ (University of Girona) for his electronic engineering support and Joan Corominas (Banyoles) for his sailing support