In the last 3 years, ECMWF introduced major upgrades to its monthly and seasonal forecast systems, with the introduction of The seasonal-fc. System-3 in March 2007 and a unified EPS-monthly system in March 2008. The purpose of the talk is to review the prospects for further evolution of these systems, focusing on three topics:
1) Current work on the development of a new seasonal forecast system (System 4) using the NEMO ocean model. Comparisons of model biases and predictive skill against System-3 from a preliminary 20-year hindcast set covering the ERA-Interim period will be presented, and provisional operational plans will be discussed.
2) Predictability arising from MJO teleconnections in extended monthly integrations. Advances in physical parametrizations included in recent cycles of the ECMWF atmospheric model (IFS) led to substantial progress in the simulation of the MJO. A set of 45-day experiments with the EPS-monthly system showed the beneficial impact of improved modeling of MJO teleconnections on the simulation of both tropical and extratropical intra-seasonal variability. A link between MJO and NAO variability during the NH winter is supported by the experimental results.
3) Experimental evidence on the impact of Arctic sea-ice variability on the N.Hem. summertime circulation and its predictability. Ensemble experiments for the 2007 and 2008 summer seasons with System 3 showed the potential for better prediction of summertime variability over Europe from a dynamical simulation of sea-ice variability. On the other hand, they highlighted the strong sensitivity of the atmospheric response to North Atlantic SST, and consequently to the coupled-model biases in this region.