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Original Research Papers

Using flow geometry for drifter deployment in Lagrangian data assimilation

Authors:

H. Salman ,

Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC, US; Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, CB3 0WA, GB
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K. Ide,

Department of Atmospheric and Oceanic Sciences & Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, US
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C. K. R. T. Jones

Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC, US
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Abstract

Methods of Lagrangian data assimilation (LaDA) require carefully chosen sites for optimal drifter deployments. In this work, we investigate a directed drifter deployment strategy with a recently developed LaDA method employing an augmented state vector formulation for an Ensemble Kalman filter. We test our directed drifter deployment strategy by targeting Lagrangian coherent flow structures of an unsteady double gyre flow to analyse how different release sites influence the performance of the method. We consider four different launch methods; a uniform launch, a saddle launch in which hyperbolic trajectories are targeted, a vortex centre launch, and a mixed launch targeting both saddles and centres. We show that global errors in the flow field require good dispersion of the drifters which can be realized with the saddle launch. Local errors on the other hand are effectively reduced by targeting specific flow features. In general, we conclude that it is best to target the strongest hyperbolic trajectories for shorter forecasts although vortex centres can produce good drifter dispersion upon bifurcating on longer time-scales.

How to Cite: Salman, H., Ide, K. and Jones, C.K.R.T., 2008. Using flow geometry for drifter deployment in Lagrangian data assimilation. Tellus A: Dynamic Meteorology and Oceanography, 60(2), pp.321–335. DOI: http://doi.org/10.1111/j.1600-0870.2007.00292.x
  Published on 01 Jan 2008
 Accepted on 5 Nov 2007            Submitted on 21 Nov 2006

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