Citation: Shen, S., J.-J. Liu, and B. Wang, 2014: An extension of the dimension-reduced projection 4DVar, Atmos. Oceanic Sci. Lett., 7, **, doi:10.3878/j.issn.1674-2834.13.0087.

http://159.226.119.58/aosl/EN/abstract/abstract461.shtml

In this paper, we present a nonlinear correction process to the dimension-reduced projection 4DVar (DRP-4DVar), one of the 4D-ensenble-variational methods of data assimilation which avoids the use of adjoint model and is very easy to solve but has the problem of linear approximation. This nonlinear correction process is inspired by the incremental approach and adopts the concept of “outer loop” to update the cost function iteratively, and it’s very easy to implement. The results of the preliminary test using the Lorenz96 model show significant improvement due to the nonlinear correction and convince us of its great potential for further application.