Comparison of reduced-order, sequential and variational data assimilation methods in the tropical Pacific Ocean |
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| Authors: | Céline Robert Eric Blayo Jacques Verron |
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| Institution: | (1) LMC-IMAG UMR 5523 CNRS/INPG/UJF/INRIA, Grenoble, France;(2) LEGI UMR 5519 CNRS/INPG/UJF, Grenoble, France |
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| Abstract: | This paper presents a comparison of two reduced-order, sequential, and variational data assimilation methods: the singular
evolutive extended Kalman filter (SEEK) and the reduced 4D-Var (R-4D-Var). A hybridization of the two, combining the variational
framework and the sequential evolution of covariance matrices, is also preliminarily investigated and assessed in the same
experimental conditions. The comparison is performed using the twin-experiment approach on a model of the tropical Pacific
domain. The assimilated data are simulated temperature profiles at the locations of the TAO/TRITON array moorings. It is shown
that, in a quasilinear regime, both methods produce similarly good results. However, the hybrid approach provides slightly
better results and thus appears as potentially fruitful. In a more nonlinear regime, when tropical instability waves develop,
the global nature of the variational approach helps control model dynamics better than the sequential approach of the SEEK
filter. This aspect is probably enhanced by the context of the experiments in that there is a limited amount of assimilated
data and no model error. |
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| Keywords: | Ocean data assimilation Reduced-order method 4D-Var SEEK Hybrid method Tropical Pacific Ocean |
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