Directed Drifter Launch Strategies for Lagrangian Data Assimilation

Andrew C. Poje
Mathethmatics Department, College of Staten Island, City University of New York

Anne Molcard
Institute of Atmospheric Sciences and Climate, Italian National Research Council

Tamay Ozgokmen
Rosenstiel School of Marine and Atmospheric Science, Universiy of Miami

The dependence of the fidelity of a Lagrangian data assimilation scheme on the initial launch locations of the observation is studied in the context of a reduced gravity, primitive equation model of the midlatitude ocean circulation. We develop a directed drifter launch strategy based on tracking the Lagrangian manifolds emanating from strongly hyperbolic regions in a given flow field. In a series of twin assimilation experiments, the convergence of the data assimilating scheme to model truth is shown to be consistently and significantly improved by such directed launches when compared to similar, but randomly chosen, initial configurations. In general, the performance of the assimilation scheme is shown to depend strongly on the independence of the Lagrangian observations and on the temporal persistence of the velocity field corrections provided by the data. Both quantities are naturally maximized by the directed launch scheme.

Last Update: September 29, 2005