A Local Formulation of the Ensemble Transform (ET) Analysis Perturbation Scheme

Abstract

Abstract Following ideas from the local ensemble transform Kalman filter, a local formulation of the ensemble transform (ET) analysis perturbation scheme is developed by partitioning the numerical weather prediction model domain into latitude bands or latitude–longitude blocks. In comparison with analysis perturbations from the original “global” ET formulation, analysis perturbations from the “banded” or “block” ET formulations are much more consistent with estimates of analysis error variance. Banded or block ET forecast ensembles also perform better under a variety of verification metrics than do global ET forecast ensembles. Substantial performance gains are observed for both the midlatitudes and the tropics. A local ET is scheduled to be made operational at the Fleet Numerical Meteorology and Oceanography Center.