ECMWF activities: Seasonal and sub-seasonal time scales

Development of the next‐generation seasonal forecast system. improvements in the representation of initial uncertainties in the ENS system; improving model error simulation: development of stochastic schemes for the simulation of model uncertainties; Development of the next generation medium‐range/monthly ensemble resolution upgrade ; Development of the coupled system used for ensemble prediction, and assessment of the impact of model changes on long‐term biases and forecast skill; Sub‐seasonal and seasonal time scale: assessment of predictability from the medium‐range to the seasonal scale; Development of the next‐generation seasonal forecast system. This is only a partial report on the ECMWF activities that might be relevant to the present meeting. During the past year they have been several improvement in the representation of the initial Uncert. In particular in the computation of the Ensemble data Assimilation as well as few adjustments in the stochastic physics scheme.

introduction of dynamical sea‐ice modelling; Improvements in the configuration and components of the coupled model used for the medium range (since Nov.2013 Ens is based on a coupled system): increase in the horizontal resolution of the atmospheric model (to 20Km in leg A ) introduction of the ORCA25_L75 (ie ¼‐degree resolution, 75 vert. levels) version of the NEMO ocean model; introduction of dynamical sea‐ice modelling; extension of leg B to 46 (implemented operationally); After the horizontal resolution upgrade in the atmospheric model and the implementation of the ¼‐degree version of NEMO, it is also planned to examine whether the extension of leg A from 10 to 15 days would benefit the forecast skill after day 10. 20km/32km vs 32km/60km

Next seasonal forecast system: an IFS cycle with reduced tropical biases and improved stratospheric processes; the availability of ERA‐NRT data for the initialization of the re‐forecasts; if necessary, an additional scheme to prepare stratospheric initial conditions; the availability of a suitable ocean re‐analysis/analysis, ideally based on ERA‐NRT forcing; improved consistency in the specification of land‐surface initial conditions between re‐forecast and real‐time runs, possibly through the use of an off‐line land‐surface analysis; a physically realistic and computationally efficient version of NEMO in the ORCA25_L75 configuration; an increased resolution of the atmospheric component a dynamical sea‐ice model with stable behavior on long time scales and adequate initial conditions. In good shape by the end of 2016

Ocean re-analysis ORAP5 a prototype for the high resolution analysis has been Developed. (ORCA25L75 NEMO driven by Era interim fluxes. ORAS5 (future oper. Analysis) will be based on ORAP5 with few mods. CERA weekly coupled data assimilation system, uses a fully coupled model that combines the IFS atmospheric model with the NEMO ocean model. The scheme is based on an incremental variational approach. It also Includes a mechanism for constraining drift in the coupled model using observational estimates of monthly averaged SST. T159L91 (~125 km) for the atmosphere and 10x10 with 42 vertical levels for the ocean. Reanalysis IFS Cy40r3 in operations. It will benefit from numerous improvements introduced in the IFS since 2006, but this cycle is particularly important for reanalysis because of the implementation of new climate fields and the treatment of unresolved lakes. The planned resolution for the new reanalysis is T511L91 (39km horizontal, 91 vertical levels). It will use a lower‐resolution 10‐member EDA configuration with a 12h 4D‐Var analysis.