Papers by Guglielmo Lacorata
Ocean Modelling, 2002
Three different data sets of numerical drifters are obtained with degrading the time sampling (1 ... more Three different data sets of numerical drifters are obtained with degrading the time sampling (1 day, 1 month and 1 year) of the Eulerian velocity field computed from a Mediterranean general circulation model. The Finite-Scale Lyapunov Exponent (FSLE) technique is used to characterize, for each of the three data sets, Lagrangian dispersion properties in relation to the time resolution of the field. In particular, we are interested in measuring the unpredictability of trajectories due to the uncertainty in the knowledge of the velocity field. Our data analysis indicates that surface relative dispersion of the Mediterranean Sea has two regimes: exponential spreading due to chaotic advection at small scales ($mesoscale) and super-diffusion at larger scales (up to $sub-basin scales). In this scenario, it is shown that trajectory evolution is most sensitive to the time sampling of the field at small spatial scales, while, at scales larger than $100 km, it is essentially independent from the details of the models. Also, FSLE is employed to visualize the geographical regions characterized by high Lagrangian unpredictability. The relation of FSLE with common oceanographic observables (e.g., local shear, velocity variance) is discussed. Ó
Lagrangian drifter dispersion in the southwestern Atlantic Ocean
Arxiv preprint arXiv: …, 2011
... Stefano Berti ... At this regard, one presently debated issue is the role of submesoscale vor... more ... Stefano Berti ... At this regard, one presently debated issue is the role of submesoscale vortices (McWilliams 1985) [velocity field features of size ∼ O(1) km] in determining the shape of the energy spectrum at intermediate scales between the Rossby deformation radius [in the ...
9 Atmospheric Dispersion with a Large-Eddy Simulation: Eulerian and Lagrangian Perspectives
The EOLE Experiment is revisited to study turbulent processes in the lower stratosphere circulati... more The EOLE Experiment is revisited to study turbulent processes in the lower stratosphere circulation from a Lagrangian viewpoint and resolve a discrepancy on the slope of the atmospheric energy spectrum between the work of and recent studies using aircraft data. Relative dispersion of balloon pairs is studied by calculating the Finite Scale Lyapunov Exponent, an exit time-based technique which is particularly efficient in cases where processes with different spatial scales are interfering. Our main result is to reconciliate the EOLE dataset with recent studies supporting a k −5/3 energy spectrum in the range 100-1000 km. Our results also show exponential separation at smaller scale, with characteristic time of order 1 day, and agree with the standard diffusion of about 10 7 m 2 s −1 at large scales. A still open question is the origin of a k −5/3 spectrum in the mesoscale range, between 100 and 1000 km.
‘Relative dispersion in the Adriatic Sea: Lagrangian data and chaotic model
Relative dispersion in the Adriatic Sea
Hierarchical Markovian modeling of multi-time systems
Relaxation of finite perturbations
GABRIEL G. KATUL, LARRY MAHRT, DAVIDE POGGI and CHRISTOPHE SANZ/One-and Two-Equation Models for Canopy Turbulence 81–109 SYLVAIN DUPONT, TANYA L. OTTE and JASON KS CHING/Simulation of Meteorological Fields within and
Lagrangian diagnostics of transport properties, barrier effects and mixing rates for the stratospheric polar vortex through a dynamical systems approach (FSLE)
Data analysis and modelling of Lagrangian drifters in the Adriatic Sea
Journal of The Atmospheric Sciences - J ATMOS SCI, 2004
The EOLE experiment is revisited to study turbulent processes in the lower stratosphere circulati... more The EOLE experiment is revisited to study turbulent processes in the lower stratosphere circulation from a Lagrangian viewpoint and to resolve a discrepancy on the slope of the atmospheric energy spectrum between the work of Morel and Larchevêque and recent studies using aircraft data. Relative dispersion of balloon pairs is studied by calculating the finite-scale Lyapunov exponent, an exit-time-based technique that is particularly efficient in cases in which processes with different spatial scales are interfering. The main goal is to reconciliate the EOLE dataset with recent studies supporting a k-5/3 energy spectrum in the 100 1000-km range. The results also show exponential separation at smaller scales, with a characteristic time of order 1 day, and agree with the standard diffusion of about 107 m2 s-1 at large scales. A remaining question is the origin of a k-5/3 spectrum in the mesoscale range between 100 and 1000 km.
Atmospheric Dispersion with a Large-Eddy Simulation
Modeling and Applications, 2009
Journal of Geophysical Research: Oceans, 2014
The Mediterranean Forecasting System (MFS) Ocean Model, provided by 4 INGV, has been chosen as ca... more The Mediterranean Forecasting System (MFS) Ocean Model, provided by 4 INGV, has been chosen as case study to analyze Lagrangian trajectory pre-5 dictability by means of a dynamical systems approach. To this regard, nu-6 merical trajectories are tested against a large amount of Mediterranean drifter 7 data, used as sample of the actual tracer dynamics across the sea. The sep-8 aration rate of a trajectory pair is measured by computing the Finite-Scale 9 Lyapunov Exponent (FSLE) of first and second kind. An additional kine-10 matic Lagrangian model (KLM), suitably treated to avoid "sweeping"-related 11 problems, has been nested into the MFS in order to recover, in a statistical 12 sense, the velocity field contributions to pair particle dispersion, at mesoscale 13 level, smoothed out by finite resolution effects. Some of the results emerg-14 ing from this work are: a) drifter pair dispersion displays Richardson's tur-15 bulent diffusion inside the [10-100] km range, while numerical simulations 16 of MFS alone (i.e. without subgrid model) indicate exponential separation; 17 b) adding the subgrid model, model pair dispersion gets very close to observed 18 data, indicating that KLM is effective in filling the energy "mesoscale gap" 19 present in MFS velocity fields; c) there exists a threshold size beyond which 20 pair dispersion becomes weakly sensitive to the difference between model and 21 "real" dynamics; d) the whole methodology here presented can be used to 22 quantify model errors and validate numerical current fields, as far as fore-23 casts of Lagrangian dispersion are concerned.
Annales Geophysicae, 2001
We analyze characteristics of drifter trajectories from the Adriatic Sea with recently introduced... more We analyze characteristics of drifter trajectories from the Adriatic Sea with recently introduced nonlinear dynamics techniques. We discuss how in quasienclosed basins, relative dispersion as function of time, a standard analysis tool in this context, may give a distorted picture of the dynamics. We further show that useful information may be obtained by using two related nonasymptotic indicators, the Finite-Scale Lyapunov Exponent (FSLE) and the Lagrangian Structure Function (LSF), which both describe intrinsic physical properties at a given scale. We introduce a simple chaotic model for drifter motion in this system, and show by comparison with the model that Lagrangian dispersion is mainly driven by advection at sub-basin scales until saturation sets in.
Journal of the Atmospheric Sciences, 2008
We introduce a 3D multiscale kinematic velocity field as a model to simulate Lagrangian turbulent... more We introduce a 3D multiscale kinematic velocity field as a model to simulate Lagrangian turbulent dispersion. The incompressible velocity field is a nonlinear deterministic function, periodic in space and time, that generates chaotic mixing of Lagrangian trajectories. Relative dispersion properties, e.g. the Richardson's law, are correctly reproduced under two basic conditions: 1) the velocity amplitudes of the spatial modes must be related to the corresponding wavelengths through the Kolmogorov scaling; 2) the problem of the lack of "sweeping effect" of the small eddies by the large eddies, common to kinematic simulations, has to be taken into account. We show that, as far as Lagrangian dispersion is concerned, our model can be successfully applied as additional sub-grid contribution for Large Eddy Simulations of the planetary boundary layer flow.
Evidence for ak^{-5/3} spectrum from the EOLE Lagrangian balloons in the low stratosphere
... balloons in the low stratosphere Guglielmo Lacorata1, Erik Aurell2, Bernard Legras3 and Angel... more ... balloons in the low stratosphere Guglielmo Lacorata1, Erik Aurell2, Bernard Legras3 and Angelo Vulpiani4 1CNR, Institute for Atmospheric and Climate Sciences, Lecce, Italy ... 2002, Boffetta et al. 2001, LaCasce and Ohlmann 2003, Gioia et al. 2003) and also in ...
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 2009
One of the major issues concerning the study of a dynamical system is the response to perturbatio... more One of the major issues concerning the study of a dynamical system is the response to perturbations. In climate dynamics, for example, it is of major interest to understand how a given variable, e.g., the temperature, is sensitive to alterations of some other component of the system, e.g., the greenhouse gas concentration. We review the connection between equilibrium and non-equilibrium properties, also known as Fluctuation-Relaxation Relation, and its main aspects in chaotic and turbulent systems. We consider, in particular, the effects of the fast variables on the slow variables in a multiscale system, as far as the sensitivity properties are concerned. Two examples about (widely speaking) climate modelling are discussed: the Lorenz-96 model and the double-potential well model. Both of them, despite their apparent simplicity, hide the same kind of interesting features of much more complex systems.
Nonlinear Processes in Geophysics, 2007
We show how a general formulation of the Fluctuation-Response Relation is able to describe in det... more We show how a general formulation of the Fluctuation-Response Relation is able to describe in detail the connection between response properties to external perturbations and spontaneous fluctuations in systems with fast and slow variables. The method is tested by using the 360-variable Lorenz-96 model, where slow and fast variables are coupled to one another with reciprocal feedback, and a simplified low dimensional system. In the Fluctuation-Response context, the influence of the fast dynamics on the slow dynamics relies in a non trivial behavior of a suitable quadratic response function. This has important consequences for the modeling of the slow dynamics in terms of a Langevin equation: beyond a certain intrinsic time interval even the optimal model can give just statistical prediction.
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Papers by Guglielmo Lacorata