Lagrangian transport in a microtidal coastal area: the Bay of Palma, island of Mallorca, Spain

Coastal transport in the Bay of Palma, a small region in the island of Mallorca, Spain, is characterized in terms of Lagrangian descriptors. The data sets used for this study are the output for two months (one in autumn and one in summer) of a high resolution numerical model, ROMS, forced atmospherically and with a spatial resolution of 300 m. The two months were selected because its different wind regime, which is the main driver of the sea dynamics in this area. Finite-size Lyapunov Exponents (FSLEs) were used to locate semi-persistent Lagrangian coherent structures (LCS) and to understand the different flow regimes in the Bay. The different wind directions and regularity in the two months have a clear impact on the surface Bay dynamics, whereas only topographic features appear clearly in the bottom structures. The fluid interchange between the Bay and the open ocean was tudied by computing particle trajectories and Residence Times (RT) maps. The escape rate of particles out of the Bay is qualitatively different, with a 32$$ more of escape rate of particles to the ocean in October than in July, owing to the different geometric characteristics of the flow. We show that LCSs separate regions with different transport properties by displaying spatial distributions of residence times on synoptic Lagrangian maps together with the location of the LCSs. Correlations between the time-dependent behavior of FSLE and RT are also investigated, showing a negative dependence when the stirring characterized by FSLE values moves particles in the direction of escape

Influence of the NAO on the northwestern Mediterranean wave climate

RESUMEN. Influencia de la nao en el clima marítimo del Mediterráneo noroccidental. – El presente trabajo estudia las teleconexiones entre la Oscilación del Atlántico Norte (NAO ) y el clima marítimo en el Mediterráneo noroccidental, definido por la media mensual de la altura significante (SWH) y la media mensual de la altura significante correspondiente al percentil 95 (percentil 95 SWH), en el período comprendido entre 1958 y 2001. Los datos analizados corresponden al retroanálisis de 44 años de datos atmosféricos, dentro del marco del proyecto HIPOCAS . Estos datos han sido codificados en forma de EOF s para obtener la variabilidad espacio-temporal asociada a la NAO . Los datos utilizados han sido previamente blanqueados para evitar correlaciones ficticias entre las series, mediante el ajuste a un modelo autorregresivo de orden p. Los resultados muestran como el clima marítimo del Mediterráneo noroccidental está influenciado a escala mensual por las distintas fases de la NAO . Cuando la NAO está en su fase positiva, podemos observar anomalías positivas en la altura significante media mensual, así como en la altura de ola correspondiente al percentil 95, estas anomalías aparecen en la zona comprendida entre las Islas Baleares, el Golfo de León y la costa catalana.ABSTRACT. This study examines teleconnections between the North Atlantic Oscillation (NAO ) and the wave climate of the northwestern Mediterranean Sea (NWM), defined by the monthly mean significant wave height (SWH) and the 95th percentile significant wave height (95th percentile SWH), in the period ranging from 1958 to 2001. The data analyzed comes from the multidecadal hindcast over Europe carried out during the HIPOCAS project. In order to avoid fictitious cross-correlations, data were prewhitened by fitting a p-order autoregressive model. To split the temporal and spatial variability, an EOF encoding technique was applied to residuals before searching for teleconnections. We found the northwestern Mediterranean wave climate to be influenced by the North Atlantic Oscillation (NAO ) with an instantaneous response. When the NAO is in its positive phase, positive anomalies in the SWH and the 95th percentile SWH appear in the area between the Balearic Islands, the Gulf of Lions and the Catalonian coast

UBathy: a new approach for bathymetric inversion from video imagery

A new approach to infer the bathymetry from coastal video monitoring systems is presented. The methodology uses principal component analysis of the Hilbert transform of video images to obtain the components of the wave propagation field and their corresponding frequency and wavenumber. Incident and reflected constituents and subharmonics components are also found. Local water depth is then successfully estimated through wave dispersion relationship. The method is first applied to monochromatic and polychromatic synthetic wave trains propagated using linear wave theory over an alongshore uniform bathymetry in order to analyze the influence of different parameters on the results. To assess the ability of the approach to infer the bathymetry under more realistic conditions and to explore the influence of other parameters, nonlinear wave propagation is also performed using a fully nonlinear Boussinesq-type model over a complex bathymetry. In the synthetic cases, the relative root mean square error obtained in bathymetry recovery (for water depths 0.75m¿h¿8.0m) ranges from ~1% to ~3% for infinitesimal-amplitude wave cases (monochromatic or polychromatic) to ~15% in the most complex case (nonlinear polychromatic waves). Finally, the new methodology is satisfactorily validated through a real field site video.Postprint (published version

Obtaining directional wave characteristics in front of nearshore field sites

Peer ReviewedPostprint (published version

Narrow banded wave propagation from very deep waters to the shore

32 pages, 13 figures, 5 tablesA fully nonlinear Boussinessq-type model with several free coefficients is considered as a departure point. The model is monolayer and low order so as to simplify numerical solvability. The coefficients of the model are here considered functions of the local water depth. In doing so, we allow to improve the dispersive and shoaling properties for narrow banded wave trains in very deep waters. In particular, for monochromatic waves the dispersion and shoaling errors are bounded by ~ 2.8% up to kh = 100, being k the wave number and h the water depth. The proposed model is fully nonlinear in weakly dispersive conditions, so that nonlinear wave decomposition in shallower waters is well reproduced. The model equations are numerically solved using a fourth order scheme and tested against analytical solutions and experimental dataAuthors would like to thank support from MICINN through Project 445 CGL2011-22964. G. Simarro and R. Minguez are supported by the Spanish government through the “Ramón y Cajal” programPeer reviewe

Wave mixing rise inferred from Lyapunov exponent

We study the horizontal surface mixing and the transport induced by waves in a coastal environment. A comparative study is addressed by computing the Lagrangian Coherent Structures, via Finite Size Lyapunov Exponents, that arise in two different numerical settings: with and without wave coupled to currents. In general,we observe that mixing is increased in the area due to waves. Besides, the methodology presented here is tested by deploying a set of eight Lagrangian drifters at different locations. This dynamical approach is shown as a valuable tool to extract information about transport, mixing and residence embedded in the Eulerian time dependent velocity fields obtained from numerical models.uthors would like to thank financial support from Spanish MICINN thought projects CTM2010-16915; CGL2011-22964 and from EU through MED Programme Project TOSCA (G-MED09-425).Peer reviewe

SOFT project: a new forecasting system based on satellite data

En: Conference Remote Sensing of the Ocean and Sea Ice 2001, 20-09-2001, Toulouse, France. Eds. Charles R. Bostater, Jr., Rosalia Santoleri.-- 13 pages, 12 figures, 1 table.-- Published Online: 7 April 2003.-- Pre-print archive: http://wwwimedea.uib.es/oceanography/projects/soft/The aim of the SOFT project is to develop a new ocean forecasting system by using a combination of satellite data, evolutionary programming and numerical ocean models. To achieve this objective two steps are proposed: (1) to obtain an accurate ocean forecasting system using genetic algorithms based on satellite data; and (2) to integrate the above new system into existing deterministic numerical models. Evolutionary programming will be employed to build “intelligent” systems that, learning from the past ocean variability (provided by satellite data) and considering the present ocean state, will be able to infer near future ocean conditions. Validation of the forecast skill will be carried out by comparing the forecasts fields with satellite and in situ observations. Validation with satellite observations will provide the expected errors in the forecasting system. Validation with in situ data will indicate the capabilities of the satellite based forecast information to improve the performance of the numerical ocean models. This later validation will be accomplished considering in situ measurements in a specific oceanographic area at two different periods of time. The first set of observations will be employed to feed the hybrid systems while the second set will be used to validate the hybrid and traditional numerical model results.This work has been carried out as part of the SOFT project funded by the E. C. under contract: EVK3-CT-2000-00028. Ananda Pascual holds a doctoral fellowship from Universitat de les Illes Balears. We thank Vicente Fernandez for his fruitful comments on the interpretation of EOFs patterns related to the Mediterranean circulation.Peer reviewe