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Multiscale techniques in turbulence: application to geophysical fluids and operational oceanography

AuthorsNieves, Verònica
AdvisorTuriel, Antonio
Issue Date2008
PublisherUniversidad Politécnica de Cataluña
AbstractTurbulent ows are of major interest for scientists and engineers, playing an essential role in uid dynamics. Even though a precise denition of turbulence does not exist, it is generally assumed that turbulence is a ow regime characterized by instabilities at large Reynolds numbers. The Reynolds number is a measure of the ratio of inertial forces to viscous forces. In the ocean, Reynolds number are of the order of 106, and so ocean dynamics is strongly nonlinear involving a large spectra of processes across all space and time scales. However, the ocean seems to be very active at around 30-300 Km, which is known as mesoscale. A schematic diagram of the spatial and temporal scales of various oceanic phenomena is shown in Figure 1.1. Instabilities in the ocean explain the meandering nature of oceanic currents, which can isolate and shed eddies when the meanders reach large amplitudes [3]. Examples of such ows are high- and low-pressure systems that are formed in the Gulf Stream area (see Figure 1.2). These systems have been related to coherent structures, which are a combination of the geometrical and dynamical properties of the ow, i.e., regions containing most of the surviving vorticity [56, 47]. As it occurs in the ocean, a turbulent ow self-organizes into a collection of coherent structures [91, 140]. The smaller eddies are exposed to the strain-rate eld of these coherent structures [123]. In recent studies, coherent structures not only have been identied with vortices, but also their presence has been connected with non-Gaussian Probability Density Functions (PDFs) of velocity elds from the ocean [17, 40, 54, 51, 139]. In addition to this characteristic, a near Gaussian component is expected for the background ow. This implies that the statistical distributions of ocean velocity elds have similar characteristics to the ones of bidimensional turbulence
DescriptionMemoria de tesis doctoral presentada por Verónica U. Nieves Calatrava para optar al grado de Doctora por la Universitat Politècnica de Catalunya (UPC), realizada bajo la dirección del Dr. Antonio Turiel Martínez del Institut de Ciències del Mar (ICM-CSIC).-- 152 pages, 37 figures, 2 tables
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