FILTER 4DAn adjoint-free four-dimensional variational data

filter 4dIn this paper, we propose an efficient and practical implementation of a four-dimensional variational ensemble Kalman filter 4D-EnKF via a modified Cholesky decomposition. The mainIn this paper, we propose an efficient and practical implementation of a four-dimensional variational ensemble Kalman filter 4D-EnKF via a modified Cholesky decomposition. The main