Characterization of Lagrangian variability on forecasting time scales using Eulerian velocity field of a forecasting high resolution model of the Tyrrhenian Sea.
Volfango Rupolo, Claudia Pizzigalli, V. Artale, R. Iacono, E. Napolitano, Gianmaria Sannino
ENEA
(Abstract received 08/14/2009 for session D)
ABSTRACT
Forecast operational oceanographic models are by now available in several regional seas. In the Mediterranean the MFS ( http://www.bo.ingv.it/mfstep ) project is active from almost ten years using a hierarchy of nested models with increasing resolution. Simply computing trajectories from Eulerian velocity field is easy. The forecasting of a trajectory of a drifting object or pollutant is of paramount importance but is a really challenging task due to the intrinsic chaotic behavior of the oceanic velocity fields and to the wind-wave interactions. Neglecting these last two factors, we addressed in the last years the problem of introducing the concept of Lagrangian indeterminacy in the in an operative context. In the past the archive of Eulerian velocity fields from the global MFS was used to provide a statistics of dispersion properties in the Mediterranean basin integrating particles systematically using 2D “hindcast” velocity fields. Results were grouped in a user friendly web site (http://clima.casaccia.enea.it/riskmap ) for a direct visualization of dispersion characteristics. When possible, real Lagrangian data and statistical properties of dispersion were compared in order to quantify errors on the reproduction of the natural variability of Lagrangian dispersion by the model.
We are now using forecasting Eulerian velocity field from an high resolution model of the Tyrrhenian Sea (1/48° x 1/48°) actually running at ENEA (http://clima.casaccia.enea.it/tirreno) in order to characterize (numerical) dispersion properties in the basin.
In this presentation we will focus on this second point. In particular, after a validation of the model, several techniques commonly used to characterize 2D turbulence are used and compared integrating about 67000 particles uniformly released at surface. We use both relatively long time series of Eulerian velocity fields and 7 days velocity field, i.e the time window of the forecasting. The aim is to test the possibility of providing operative products highlighting the variability of Lagrangian dispersion in a given sub basin.
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