A New Data Assimilation Scheme : The Space-Expanded Ensemble Localization Kalman Filter

Abstract EN

This study considers a new hybrid three-dimensional variational (3D-Var) and ensemble Kalman filter (EnKF) data assimilation (DA) method in a non-perfect-model framework, named space-expanded ensemble localization Kalman filter (SELKF).

In this method, the localization operation is directly applied to the ensemble anomalies with a Schur Product, rather than to the full error covariance of the state in the EnKF.

Meanwhile, the correction space of analysis increment is expanded to a space with larger dimension, and the rank of the forecast error covariance is significantly increased.

This scheme can reduce the spurious correlations in the covariance and approximate the full-rank background error covariance well.

Furthermore, a deterministic scheme is used to generate the analysis anomalies.

The results show that the SELKF outperforms the perturbed EnKF given a relatively small ensemble size, especially when the length scale is relatively long or the observation error covariance is relatively small.