OceanMAPS v4.0i: a global eddy resolving EnKF ocean forecasting system

The Australian Bureau of Meteorology completed the first stage of a major upgrade to its operational ocean forecast system in June 2022. This interim version, referred to as OceanMAPS version 4.0i, focused on the implementation of an advanced data assimilation system based on an asynchronous ensemble Kalman Filter method. Specifically, a hybrid-EnKF method was introduced based on 48 dynamic members and 144 stationary low-mode members. OceanMAPSv4.0i shows many significant improvements over the previous system including initial conditions with improved dynamical balance and forecasts with robust reductions in mean absolute difference against all reference observations including Jason-series altimetry, Argo profiles, in situ sea surface temperature and near-surface currents.