Thursday, 17 January 2002: 2:45 PM
Drifter launch strategies based on dynamic Lagrangian templates
A basin scale, reduced gravity, primitive equation model is used to study
how drifter launch strategies affect the accuracy of Eulerian velocity fields
reconstructed from limited Lagrangian data. Optimal dispersion launch sites
are found by tracking strongly hyperbolic singular points in the flow field.
Lagrangian data from drifters launched from such locations are found to
provide significant improvement in the reconstruction accuracy over similar
but randomly located initial deployments. The eigenvalues of the hyperbolic
singular points in the flow field determine the intensity of the local
particle dispersion and thereby provide a natural time-scale for initializing
subsequent launches. Aligning the initial drifter launch in each site along
an out-flowing manifold insures both high initial particle dispersion and
the eventual sampling of regions of high Lagrangian kinetic energy, two
factors that are found to be critical to the accuracy of the Eulerian
reconstruction. Reconstruction error is reduced by a factor of 2.5
by using a continual launch strategy that incorporates both local stretching
rates and the outflowing directions of two strong saddles located
in the dynamically active region south of the central jet.
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