1,720,967 research outputs found
Laboratory simulation of polar circulation and zonal flows in rotating shallow water turbulence.
No full textLaboratory study of forced rotating shallow water turbulence
No full textDuring the last three decades several authors have studied the appearance of multiple zonal jets in planetary atmospheres and in the Earths oceans. The appearance of zonal jets has been recovered in numerical simulations (Yoden & Yamada, 1993), laboratory experiments (Afanasyev & Wells, 2005; Espa et al., 2008, 2010) and in field measurements of the atmosphere of giant planets (Galperin et al., 2001). Recent studies have revealed the presence of zonation also in the Earths oceans, in fact zonal jets have been found in the outputs of Oceanic General Circulation Models-GCMs (Nakano & Hasumi, 2005) and from the analysis of satellite altimetry observations (Maximenko et al., 2005). In previous works (Espa et al., 2008, 2010) we have investigated the impact of the variation of the rotation rate and of the fluid depth on jets organization in decaying and forced regimes. In this work we show results from experiments performed in a bigger domain in which the fluid is forced continuously. The experimental set-up consists of a rotating tank (1m in diameter) where the initial distribution of vorticity has been generated via the Lorentz force in an electromagnetic cell. The latitudinal variation of the Coriolis parameter has been simulated by the parabolic profile assumed by the free surface of the rotating fluid. Flow measurements have been performed using an image analysis technique. Experiments have been performed changing the tank rotation rate and the fluid thickness. We have investigated the flow in terms of zonal and radial flow pattern, flow variability and jet scales
Anisotropic Lagrangian Dispersion in Rotating Flows with a β Effect
No full textA detailed analysis of Lagrangian tracer dispersion is performed on datasets obtained from laboratory experiments that simulate rotating turbulence in the presence of a β effect. Compatible with the limitations of the experimental apparatus, a relatively wide range of the zonostrophy index Rβ, a parameter used to characterize flow regimes in β-plane turbulence, is explored. The considered range spans from values ̃O(10-1), for which the flow is nearly isotropic, to values ̃O(1), corresponding to the so-called transitional range in which the flow gradually leaves the friction-dominated regime to enter the full zonostrophic regime. The degree of anistropy and the characteristic scales of the flow have been estimated by means of a Lagrangian approach based on the reconstruction of tracer trajectories and on the measure of the finite-scale Lyapunov exponents (FSLE). The FSLE analysis allows one to identify the regimes of two-particle dispersion and to relate them to the physical parameters of the system. Moreover, a Lagrangian anisotropy index (LAI) is introduced and defined in terms of the FSLE zonal and radial components, in order to describe the onset of anisotropy and to check if it is consistent with the theoretical predictions. It is remarkable that the finite-scale dispersion rates are very sensitive to the degree of anistropy of turbulence, more so than other indicators defined in terms of Eulerian quantities. Furthermore, they offer an effective diagnostic tool of the degree of anisotropy that can be used even prior to attaining a fully developed regime of zonostrophic turbulence. © 2014 American Meteorological Society
Multiple zonal jets formation in forced rotating flows with a beta effect: a laboratory model
No full textZonal Jets In forced rotating shallow water turbulence: a laboratory study
No full textDuring the last three decades, the appearance of multiple zonal jets in planetary atmospheres and in the Earth’s oceans has widely studied. Evidences of this phenomenon were recovered in numerical simulations [1], laboratory experi-ments [2-4] and in field measurements of giant planets’ atmosphere [5]. Recent studies have revealed the presence of zonation also in the Earth’s oceans; in fact, zonal jets were recovered in the outputs of Oceanic General Circulation Models-GCMs [6] and from satellite altimetry observations [7]. In previous works [3-4], we have investigated the impact of several experimental parameters on jets organization both in decaying and forced regimes. This work shows new results in the context of continuously forced flows obtained performing experiments in a bigger domain. The experimental set-up consists of a rotating tank where the initial distribution of vorticity is generated via the Lorentz force in an electromagnetic cell and the latitudinal variation of the Coriolis parameter is simulated by the parabolic profile assumed by the free surface of the rotating fluid. The velocity fields were measured using an image analysis technique. The flow is characterized in terms of zonal and radial flow pattern, flow variability and jet scales
Simulating zonation in geophysical flows by laboratory experiments
No full textThe laboratory modelling of a rotating turbulent flow subjected to a beta-effect by means of laboratory experiments is considered. In particular the focus has been put on the emergence and the evolution of zonal jet-like structures due to the anisotropization of the upscale energy transfer that can be observed in geophysical flows. The experimental setup consists of a rotating tank in which a turbulent flow is reproduced by electromagnetically forcing a shallow layer of saline solution; this model then reproduces the dynamics in the polar regions simulating the so-called gamma-plane by the parabolic surface of the rotating fluid. Several experiments have been performed by changing the main external parameters in order to investigate if the setup is suitable for reproducing the basic dynamics associated with a banded configuration analogous to large scale atmospheric and oceanic circulations. Velocity measurements performed by image analysis have allowed characterization of the flow in terms of mean azimuthal velocity, degree of anisotropy, distribution of energy, and characteristic scales. As expected, zonal jets have been found to dominate the dynamics when the beta-effect is stronger. (C) 2013 AIP Publishing LLC
The emergence of zonal jets in forced rotating shallow water turbulence: A laboratory study
No full textThe emergence of a sequence of alternating intense and elongated eastward-westward bands i.e. zonal jets in the atmosphere of the giant planets and in Earth's oceans have been widely investigated. Nevertheless jets formation and role as material barriers remain still unclear. Jets are generated in a quasi-2D turbulent flow due to the latitudinal variation of the Coriolis parameter (the so-called beta-effect) which modifies the inverse cascade process channeling energy towards zonal modes. In previous experiments we have investigated the impact of the variation of the rotation rate, of the domain geometry and of the initial spectra on jets organization in a decaying regime. In this work we investigate the formation of jets in a continuously forced flow, we characterize the observed regime and also we attempt to verify the existence of an universal regime corresponding to the so-called zonostrophic turbulence. The experimental set-up consists of a rotating tank where turbulence is generated by electromagnetically forcing a shallow layer of an electrolyte solution, and the variation of the Coriolis parameter has been simulated by the parabolic profile assumed by the free surface of the fluid under rotation. Flow measurements have been performed using image analysis. Copyright (C) EPLA, 201
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