Abstract
Abstract. The Forecast Ocean Assimilation Model (FOAM) is an operational ocean analysis and forecast system run daily at the Met Office. FOAM provides modelling capability in both deep ocean and coastal shelf sea regimes using the NEMO (Nucleus for European Modelling of the Ocean) ocean model as its dynamical core. The FOAM Deep Ocean suite produces analyses and 7-day forecasts of ocean tracers, currents and sea ice for the global ocean at 1/4° resolution. Satellite and in situ observations of temperature, salinity, sea level anomaly and sea ice concentration are assimilated by FOAM each day over a 48 h observation window. The FOAM Deep Ocean configurations have recently undergone a major upgrade which has involved the implementation of a new variational, first guess at appropriate time (FGAT) 3D-Var, assimilation scheme (NEMOVAR); coupling to a different, multi-thickness-category, sea ice model (CICE); the use of coordinated ocean-ice reference experiment (CORE) bulk formulae to specify the surface boundary condition; and an increased vertical resolution for the global model. In this paper the new FOAM Deep Ocean system is introduced and details of the recent changes are provided. Results are presented from 2-year reanalysis integrations of the Global FOAM configuration including an assessment of short-range ocean forecast accuracy. Comparisons are made with both the previous FOAM system and a non-assimilative FOAM system. Assessments reveal considerable improvements in the new system to the near-surface ocean and sea ice fields. However there is some degradation to sub-surface tracer fields and in equatorial regions which highlights specific areas upon which to focus future improvements.
Highlights
The Forecast Ocean Assimilation Model (FOAM) system is an operational ocean forecasting system run daily at the Met Office which provides modelling capability in both deep ocean and shelf sea regimes
This problem appears to be much worse in the Southern Ocean, where persistence is considerably better over the latter parts of the forecast
This situation is believed to be caused by a mixing bias in the ORCA025 model, which has been highlighted by the change in surface boundary condition (SBC) from direct forcing to coordinated ocean-ice reference experiment (CORE) bulk formulae
Summary
The Forecast Ocean Assimilation Model (FOAM) system is an operational ocean forecasting system run daily at the Met Office which provides modelling capability in both deep ocean and shelf sea regimes. Ocean and sea ice analyses from the Global FOAM configuration are used as initial conditions for the Met Office’s GloSea coupled ocean– ice–atmosphere seasonal and medium-range forecasting systems (MacLachlan et al, 2014). The new system retains the NEMO ocean model which is coupled to the Los Alamos sea ice model (CICE) of Hunke and Lipscomb (2010) in place of NEMO’s native Louvain-la-Neuve Sea Ice Model 2 (LIM2: Fichefet and Maqueda, 1997; Bouillon et al, 2009) This change from the LIM2 model to CICE was driven by the need to be consistent with the Met Office seasonal forecasting (GloSea; MacLachlan et al, 2014; Arribas et al, 2011) and climate modelling (HadGEM; Hewitt et al, 2011; Johns et al, 2006) systems to support the Met Office’s aim of producing seamless forecasts across all timescales (Brown et al, 2012).
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