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Observing Turbulence Regimes and Lagrangian Dispersal Properties in the Oceans
Volfango Rupolo
ENEA
rupolo@casaccia.enea.it(Abstract received 04/20/2005 for session B)
ABSTRACT
In this talk we will show that the ratio y=Ta/Tv between the acceleration and velocity time scale, directly estimated from the lagrangian trajectory, is an useful index to rationalize the analysis of real Lagrangian trajectories and to avoid a mixture of different regimes, when averaging quantities. We analyzed sub-surface floats data in the Atlantic basin and surface drifters data in the world oceans obtained through the WOCE archive (2002) and we observed that trajectories having respectively a small value of y, and a complex conjugates pair of time scales, belong to two extreme classes, characterized by different shapes, correlation and dispersal properties. In particular, the Lagrangian correlation length varies according to the energy very differently, indicating that this index is an useful tool to discriminate between the two limiting cases in which the spatial structure is strong or weak. On the other hand, the spectral and correlation properties of trajectories belonging to the same class in different datasets are similar. These observations allow us to estimate the role of the diverse regimes in the particles dispersion, both in time and in the geographical space. The dimensionless form of the structure function shows that coherent structures, when present, prevail in the Lagrangian dispersion only for time smaller than 4-5 T_L, where T_L is the Lagrangian correlation time. The same analysis, performed in the dimensional space, has lead to the characterization of the role of the coherent structures in the dispersion in the sub-surface in the Atlantic basin.
- WOCE Data Products Committee. 2002. WOCE Global Data: Subsurface Floats and Surface Velocity Data, Version 3.0, WOCE International Project Office, Report 180/02, Southampton, UK
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005