Model: NEMO coupled ice-ocean model v2.3
Configuration: ORCA025_LIM2 (1/4o by 46 vertical levels)
Data assimilated: UR025.3 assimilates in situ temperature and salinity observations that were obtained from the UK Met Office quality controlled ENACT/ENSEMBLES (EN3_v2a) dataset available from (http://www.metoffice.gov.uk/hadobs/en3/). A detailed description of the data set including the quality control processing is presented in Ingleby and Huddleston (2007). Assimilation method: Temperature profiles (T) are assimilated along with a salinity balancing increment following the method of Troccoli and Haines, 1999). Salinity profiles (S) are then assimilated along isotherms (i.e., S(T)) up to latitudes of around 50oN/S, using the methodology described by Haines et al. (2006). At higher latitudes salinity is assimilated in a univariate way on z levels. Model – data differences (innovations) are evaluated at the closest model time step, and assimilation increments are calculated every 5 days. Increments are then introduced into the model evenly over the following day (Incremental Analysis Updating, Bloom et al., 1996). Smith and Haines (2009) give more details of the assimilation methodology. Surface Forcing: Surface atmospheric forcing for UR025.3 is obtained from ECMWF ERA-Interim atmospheric reanalysis (Simmons et. al., 2007; Dee and Uppala, 2009; Dee et al., 2011). The ERA-Interim reanalysis provides 10-m wind, 2-m air humidity and 2-m air temperature to compute 6-hourly turbulent air/sea and air/sea-ice fluxes during model integration, using the bulk formula proposed by Large and Yeager (2004, 2009). Downwelling short and long wave radiative fluxes and precipitation are also provided by ERA-Interim. The river runoff is Dai and Trenberth (2002). To prevent drift in the density distributions, a sea surface salinity relaxation to the WOA05 climatology, Boyer et al (2006), is applied with a timescale of 180 days for the top 10 m at the ice-free surface, decreasing to 36 days under ice.