2023_SI-WWRP-1_S2S_report_Phase 2-2_en

2.1 Summary of Phase 1 A primary goal of the first phase of the S2S project was to assess the current capabilities of state-of-the-art operational sub-seasonal to seasonal forecasts and identify gaps and issues and evaluate the potential usefulness of S2S forecasts for various applications. [...] Figure 2: Structure of Phase 2 of the WWRP/WCRP S2S project (2018–2023) 6 3 SCIENCE 3.1 Science Subproject achievements 3.1.1 Madden-Julian oscillation/teleconnections The MJO and its teleconnections to the extratropics represent one of the primary sources of predictability in the extratropics on the S2S timescales. [...] Beyond the second week, in the current generation of models, the amplitude of MJO teleconnections to the North Pacific and the Euro-Atlantic sector continues to be underestimated as in the previous versions of the models evaluated by Vitart (2017). [...] The MJO can modify the preferred evolution of the atmospheric flow over the North Atlantic region such as the North Atlantic Oscillation (NAO), and the teleconnection depends on the ENSO phase (Lee et al., 2019). [...] In the extratropics, the IG waves in the geopotential height are about a factor of 10 smaller than the Rossby waves and about a factor of 2–3 lower in wind speed albeit the IG response to the MJO is more coherent than the Rossby-wave response (Franzke et al., 2019).