1224 Ocean Dynamics (2019) 69:1217–1237 Fig. 5 Surface temperature averaged for July 2012. Shown are (upper row) RMS error with regard to the assimilated observations for the experiment FREE, (middle) RMSE for the experiment WEAK, (bottom) change in temperature due to the assimilation. The assimila- tion result to changes up to 2 ?C which strongly reduces the RMSE in both grids