Initialization: Weakly Coupled Assimilation: Description Analyses

The Goddard Earth Observing System integrated Ocean Data Assimilation System (GEOS iODAS) is a system for both ocean and sea-ice data assimilation. It is integrated within the broader GEOS model and data assimilation system using the Earth System Modeling Framework (ESMF). By using an object-oriented framework, the analysis systems are model-independent, but have been implemented and tuned for the Modular Ocean Model Version 4.1 (MOM4.1) developed by the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) and the CICE model developed by Los Alamos National Laboratory.

One of the purposes of the A005 and A004 ocean and sea-ice analyses is to provide consistent initial conditions for all the model components present in the CM1 framework as an initialization of seasonal hindcasts and forecasts with GEOS-5, from 1980 to present. CM1, replaying MERRA and assimilating SST, SSS and sea-ice observations, was used to provide all initial conditions except for the ocean. Because of discrepancies in the climatology of the hydrological cycle in MERRA (Reichle et al. 2011), a correction to the MERRA precipitation fields was applied during the replay. The correction is based on the v2.1 product from the Global Precipitation and Climatology Project (GPCP) prior to September 2009 and the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), rescaled to be consistent with the GPCP climatology, from September 2009 to the present.

A004 differs from A005 in several ways: along track altimeter data are assimilated and no climatological profiles of T and S were assimilated during the Argo period. A005 was started at the beginning of the altimeter period in January 1993 from initial conditions provided by A005. Due to time constraints, the assimilation of all ocean observations except sea-ice concentration were performed within the CM2 framework, forced with atmospheric fluxes obtained from the CM1 simulations. For A005, the fluxes were obtained from the CM1 run described above, replaying MERRA but with a correction to the precipitation, assimilating SST, sea-ice concentration and SSS climatology. Unfortunately, one of the artifacts of the precipitation correction is the loss of the water budget closure, which resulted in the ocean component losing water. Hence, A004 followed the same procedure, but with no correction to precipitation.