  We propose an improvement of an oceanographic three dimensional variational
assimilation scheme (3D-VAR), named OceanVar, by introducing a recursive filter
(RF) with the third order of accuracy (3rd-RF), instead of a RF with first
order of accuracy (1st-RF), to approximate horizontal Gaussian covariances. An
advantage of the proposed scheme is that the CPU's time can be substantially
reduced with benefits on the large scale applications. Experiments estimating
the impact of 3rd-RF are performed by assimilating oceanographic data in two
realistic oceanographic applications. The results evince benefits in terms of
assimilation process computational time, accuracy of the Gaussian correlation
modeling, and show that the 3rd-RF is a suitable tool for operational data
assimilation.
