Retrospective High Resolution Three-Dimensional Variational Ocean Data Assimilation Experiments for MOM6-CICE6 in UFS Weather Model with RTOFS-DA Data Assimilation

Preliminary high resolution (1/12°) global ocean data assimilative experiments are performed, using the framework of the community based Unified Forecast System-Weather Model (UFS-WM). Presently the operational Real Time Ocean Forecast System version 2.4 (RTOFSv2.4) consists of the HYbrid Coordinates Ocean Model (HYCOM) coupled to the Los Alamos Sea Ice (CICE4), and RTOFS-DA, a multivariate multi-scale 3-D var data assimilation (DA) system. In the future, RTOFS will transition to the UFS-based operational system with JEDI/SOCA data assimilation.

A transient intermediate version for the system has been developed and is being tested, consisting of coupled MOM6/CICE6 within the UFS-WM-data-atmosphere, with RTOFS-DA as the DA system. A first experiment is done assimilating a complete set of ocean observations: sea surface temperature and salinity (SST and SSS) from satellites and from in-situ platforms, in-situ profiles of temperature and salinity, Absolute Dynamic Topography (ADT) derived from altimeters, but no ice assimilation. The data assimilation system is RTOFS-DA in the version included in the current development RTOFS v2.5. Ice assimilation is to be included in next experiments. Results are discussed and compared with RTOFS/HYCOM, for model features including Gulf Stream frontal position, and surface and subsurface errors.