Abstract. We develop a new Earth System model configuration framed into the ICON architecture, which provides the baseline for the next generation of climate predictions and projections (hereafter ICON XPP – where XPP stands for eXtended Predictions and Projections). ICON XPP is an outcome of a joint project between climate research institutes and the Deutscher Wetterdienst, integrating numerical weather prediction and Earth System modeling and prediction based on the ICON framework. ICON XPP comprises the atmospheric component as used for the numerical weather prediction (ICON NWP), the ICON ocean and land surface components, and an ensemble-variational data assimilation system, all adjusted to an Earth System model for pursuing climate research and operational climate forecasting. Here, two baseline configurations are presented, one with a 160 km atmosphere and a 40 km ocean resolution, and one with 80 km atmosphere and 20 km ocean resolution, and a first evaluation is pursued based on the CMIP DECK (Diagnostic, Evaluation and Characterization of Klima) experimentation framework. Emphasis is given to the basic assessment of their mean climate, trends and climate sensitivity, and key processes in the tropics and mid-latitudes are examined, which are of relevance for climate predictions.

ICON XPP is able to depict the basic properties of the coupled climate. The pre-industrial climate shows a balanced radiation budget at the top-of-atmosphere and a mean global near-surface temperature of about 13.8–14 °C. The ocean shows circulation strengths in the range of the observed values, such as the AMOC at 16–18 Sv and the flows through the common passages. The current climate is characterized by a trend in the global mean temperature of ~1.2 °C since the 1850s, close to what is found in reference datasets. At regional scale, however, the hydroclimate deviates strongly from observed conditions. For example, the inter-tropical convergence zone (ITCZ) ​​is dominated by a double peak with a particular wet southern subtropical branch over the oceans. Further, the climate in the Southern Ocean is characterized by a strong positive mean bias, with the sea surface temperature too high up to 5 °C.

Key dynamical processes are presented, such as the El Niño/Southern Oscillation (ENSO) whose overall performance fits with the CMIP6-like coupled models. However, in the present configuration, the amplitude is ⅔ of the observed values, and the ENSO feedbacks are underestimated. Further, tropical waves and the Madden-Julian Oscillation are captured well, and spontaneous weak quasi-biennial oscillation is found in the 40 km atmosphere configuration. The atmospheric dynamics at the extra-tropics of both configurations is particularly noteworthy. ICON XPP exhibits a good representation of the jet stream position, particularly in the northern extra-tropics. Closer investigations show that the influences of the transient momentum transports and their feedbacks on the jet stream are well reproduced in ICON XPP. Stratospheric dynamics further reveal a sufficiently strong polar vortex and an adequate number of sudden stratospheric warmings. A clear improvement is found for all processes for the higher-resolved configuration compared to the lower resolution. Overall, ICON XPP performs at a similar level in the tested climate simulations as climate models performed in CMIP6 and forms a good basis for application in the areas of climate forecasts and projections, as well as climate research.