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2002 LAPCOD Meeting
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Assimilation of drifter observations for the reconstruction of the Eulerian circulation field

Anne Molcard(a,b), Leonid I. Piterbarg(c), Annalisa Griffa(a,b), Tamay M. Özgökmen(a) and Arthur J. Mariano(a)
(a)RSMAS/MPO, University of Miami, USA, (b)CNR, La Spezia, Italy, (c)CAMS, University of Southern California, USA
amolcard@rsmas.miami.edu

(Abstract received 09/26/2002 for session D)
ABSTRACT

In light of the increasing number of drifting buoys in the ocean, and recent advances in the realism of ocean general circulation models toward oceanic forecasting, the problem of assimilation of Lagrangian observations data in Eulerian models is investigated. A new and general rigorous approach is developed based on optimal interpolation methods, which takes into account directly the Lagrangian nature of the observations. An idealized version of this general formulation is tested in the framework of identical twin-experiments using a reduced-gravity, quasi-geostrophic model.

An extensive study is conducted to quantify the effectiveness of Lagrangian data assimilation as a function of the number of drifters, the frequency of assimilation and uncertainties associated with the forcing functions driving the ocean model. The performance of the Lagrangian assimilation technique is also compared to that of conventional methods of assimilating drifters as moving current meters, and assimilation of Eulerian data, such as fixed-point velocities. Overall the results are very favorable for the assimilation of Lagrangian observations to improve the Eulerian velocity field in ocean models. The results of our assimilation twin experiments imply an optimal sampling frequency for oceanic Lagrangian instruments in the range of 20-50% of the Lagrangian integral time scale of the flow field.

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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000