Efficient estimation of time-mean states of ocean models using 4D-Var and implicit time-stepping

A. D. Terwisscha van Scheltinga (1) , H. A. Dijkstra (1)

1 IMAU - Institute for Marine and Atmospheric Research [Utrecht]

We propose an efficient method for estimating a time-mean state of an ocean model subject to given observations using implicit time-stepping. The new method uses (i) an implicit implementation of the 4D-Var method to fit the model trajectory to the observations, and (ii) a pre-processor which applies a multi-channel singular spectrum analysis to enhance the signal-to-noise ratio of the observational data and to filter out the high frequency variability. This approach enables one to estimate the time-mean model state using larger time-steps than is possible with an explicit model. The performance of the method is presented for two test cases within a barotropic quasi-geostrophic nonlinear model of the wind-driven double-gyre ocean circulation. The method turns out to be accurate and, in comparison with the time-mean state computed with an explicit version of the model, relatively cheap in computational cost.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Sciences de la Terre

A. D. Terwisscha van Scheltinga, H. A. Dijkstra. Efficient estimation of time-mean states of ocean models using 4D-Var and implicit time-stepping. Nonlinear Processes in Geophysics, 2007, 14 (6), pp.777-788. ⟨hal-00302941⟩