Approximate Variational Method for Ocean Data Assimilation |
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| Authors: | Motoyoshi Ikeda |
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| Institution: | (1) Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan;(2) also Frontier Research System for Global Change/International Arctic Research Center, Fairbanks, Alaska, USA |
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| Abstract: | An approximate variational method is proposed to assimilate an oceanographic data set with a numerical ocean model. In the
approximate method, the adjoint equation to a governing equation is derived and then converted to a finite difference form,
in contrast to the ordinary, exact variational method which is composed of a finite difference equation adjoint to the finite
difference governing equation. A cumbersome derivation of the adjoint equation is avoided, and finite difference schemes used
for the original governing equation are easily utilized for the adjoint equation. This method has been verified with twin
experiments. The flow field in the twin experiments is composed of dipole eddies in a two-layer quasi-geostrophic model. Initial
and boundary conditions are control variables. The descent converges towards the exact field within 50 iterations, showing
that the fundamental problem of the method (an unstable descent with a large number of iterations) does not appear. The approximate
method is promising and should be tried with real data.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | Data assimilation mesoscale eddy modelling |
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